Metric Halo SpectraFoo User Manual
SpectraFoo
User’s Guide
SpectraFoo User's Guide
Metric Halo
$Revision: 1656 $
Publication date $Date: 2012-04-30 13:49:05 -0500 (Mon, 30 Apr 2012) $
Copyright © 2011 Metric Halo
Table of Contents
1. Introduction ............................................................................................................................... 11
Congratulations! ..................................................................................................................... 11
About SpectraFoo Configurations ............................................................................................. 11
Introduction ............................................................................................................................ 11
System Requirements .............................................................................................................. 12
2. SpectraFoo Basics ....................................................................................................................... 14
Getting to know SpectraFoo .................................................................................................... 14
Common Features – Instruments .............................................................................................. 14
Common Features – Control Windows ..................................................................................... 15
The Real Time Rack ............................................................................................................... 16
Real Time Rack Consolidated View .................................................................................. 17
3. Instruments ................................................................................................................................. 18
SpectraFoo Standard ............................................................................................................... 18
SpectraFoo Complete .............................................................................................................. 18
Level Meter ............................................................................................................................ 19
Overview ....................................................................................................................... 19
User-Definable Over (Digital Clip) Counter ....................................................................... 20
Sum & Difference Meter Mode ........................................................................................ 21
Detailed Readout and Hold Indicator Controls .................................................................. 21
Options Window ............................................................................................................ 21
PPM ballistics ................................................................................................................. 23
Meter scales ................................................................................................................... 24
User selectable meter bar colors ...................................................................................... 24
Meter bar color transition levels ....................................................................................... 25
Spectragraph .......................................................................................................................... 25
Overview ....................................................................................................................... 25
Dual channel modes ....................................................................................................... 26
Sum, Multiply and Overlap modes ................................................................................... 27
Accumulation modes ...................................................................................................... 28
Physical unit calibration .................................................................................................. 29
Trace colors ................................................................................................................... 30
Octave Analysis .............................................................................................................. 30
Log and linear averaging ................................................................................................. 33
Spectral Snapshots, Overlays & Libraries ........................................................................... 33
Spectragram ........................................................................................................................... 38
Oscilloscope .......................................................................................................................... 41
Overview ....................................................................................................................... 41
Single and Dual channel modes ...................................................................................... 43
Trace display modes ....................................................................................................... 43
Selectable trigger channel ................................................................................................ 44
Power History ........................................................................................................................ 44
Envelope History .................................................................................................................... 44
Power Balance History ............................................................................................................ 45
Lissajous Phase Scope ............................................................................................................. 45
Vectorscope and X-Y modes ............................................................................................ 45
Stereo Position mode ...................................................................................................... 46
Adjustable sensitivity ....................................................................................................... 46
Auto-Sensitivity Mode ..................................................................................................... 47
Hi-Res Mode .................................................................................................................. 47
Phase Torch™ ........................................................................................................................ 47
Band Power History ................................................................................................................ 49
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SpectraFoo User's Guide
Timecode Clock ..................................................................................................................... 49
Correlation Meter ................................................................................................................... 49
Correlation History Meter ........................................................................................................ 50
Code Meter ............................................................................................................................ 51
Code Matrix Meter ................................................................................................................. 51
Code List Meter ...................................................................................................................... 52
THD Meter ............................................................................................................................ 53
4. The Transfer Function ................................................................................................................. 55
Overview ............................................................................................................................... 55
Transfer Function Controls ..................................................................................................... 58
Coherence .............................................................................................................................. 60
The Transfer Function Window ................................................................................................ 60
Understanding the Transfer Function ........................................................................................ 62
Interpreting the Data ............................................................................................................... 67
About the Response Curves ..................................................................................................... 70
Measuring System Response .................................................................................................... 71
System Correction ................................................................................................................... 73
Transfer Function Snapshot Overlays Reference ......................................................................... 73
Cursors in the Transfer Function window .................................................................................. 75
5. Controlling Audio and Instruments ............................................................................................... 76
Analyzer Control & Routing .................................................................................................... 76
Analyzer Channels .................................................................................................................. 78
Adjusting the Number of Analyzer Channels ............................................................................. 79
Changing the analysis depth .................................................................................................... 80
Configuring the routing matrix ................................................................................................. 80
Difference monitoring for all instruments .................................................................................. 82
Routing the Signal Generator Output [SFC] ............................................................................... 83
6. Physical Unit Calibration ............................................................................................................. 84
7. Workflow Features ...................................................................................................................... 85
Overview ............................................................................................................................... 85
Window Sets .......................................................................................................................... 86
Link Groups ........................................................................................................................... 87
8. Signal Generator ......................................................................................................................... 90
Overview ............................................................................................................................... 90
Sweepable sine waves ............................................................................................................ 90
Additive white noise with sweepable level ................................................................................ 91
Additive pink noise with sweepable level ................................................................................. 92
Dither & Quantization ............................................................................................................ 92
FFT Synchronization ............................................................................................................... 93
Windowed Bursts ................................................................................................................... 94
Arbitrary signal sample rates .................................................................................................... 94
Building Files & Captures ........................................................................................................ 94
9. Controlling the FFT Window ....................................................................................................... 96
10. Capture and Storage .................................................................................................................. 97
Recording Captures ................................................................................................................. 97
Loading Audio Files for Capture ............................................................................................... 99
Capture List Window .............................................................................................................. 99
Capture Overview Windows .................................................................................................... 99
Understanding the Overview Window ............................................................................ 100
Measuring time between two events ............................................................................... 104
Data Slicing ................................................................................................................. 104
11. Quick Menu Reference ............................................................................................................ 105
Main .................................................................................................................................... 105
File ...................................................................................................................................... 107
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SpectraFoo User's Guide
Edit ...................................................................................................................................... 107
Analyzer .............................................................................................................................. 108
Audio I/O ............................................................................................................................. 108
Captures ............................................................................................................................... 109
Groups ................................................................................................................................. 109
Window ............................................................................................................................... 109
12. Epilogue ................................................................................................................................. 111
13. License Agreement .................................................................................................................. 112
Glossary ....................................................................................................................................... 115
Index ........................................................................................................................................... 121
5
List of Figures
2.1. Power button ......................................................................................................................... 14
2.2. Solo button ............................................................................................................................ 14
2.3. Parameter control button ......................................................................................................... 14
2.4. Real Time Rack Control buttons ............................................................................................... 15
2.5. Active Channel pop-up menu (with custom channel names) ....................................................... 15
2.6. Instrument Groups Menu – Only applies to instruments in the Real Time Rack .............................. 16
2.7. Real Time Rack ...................................................................................................................... 17
3.1. Level Meter Horizontal Orientation .......................................................................................... 19
3.2. Level Meter Vertical Orientation .............................................................................................. 19
3.3. Digital Level Meters (Peak, RMS and VU meters w/ Clipped Sample Counter) ............................... 20
3.4. Over Counter ......................................................................................................................... 21
3.5. Level Meter Controls Window ................................................................................................. 21
3.6. Level Meter Options Window .................................................................................................. 22
3.7. Level Meter Options Window .................................................................................................. 24
3.8. The Spectragraph and controls ................................................................................................. 26
3.9. Spectragraph showing the left and right channels of a stereo pair ................................................ 27
3.10. Spectragraph Second Traces pop-up ....................................................................................... 28
3.11. Accumulation Mode pop-up .................................................................................................. 28
3.12. Pink Noise with Pink is Flat ................................................................................................... 29
3.13. Pink Noise with White is Flat ................................................................................................ 29
3.14. White Noise with Pink is Flat ................................................................................................ 29
3.15. White Noise with White is Flat .............................................................................................. 29
3.16. Accessing Trace Color controls .............................................................................................. 30
3.17. The Mac OS color picker ...................................................................................................... 30
3.18. Spectragraph display Resolution pop-up .................................................................................. 31
3.19. 1 octave display resolution .................................................................................................... 31
3.20. 1/2 octave display resolution ................................................................................................. 31
3.21. 1/3 octave display resolution ................................................................................................. 32
3.22. 1/6 octave display resolution ................................................................................................. 32
3.23. 1/12 octave display resolution ............................................................................................... 32
3.24. 1/24 octave display resolution ............................................................................................... 33
3.25. Spectragraph Snap Button ...................................................................................................... 34
3.26. The Spectral Snapshots dialog ................................................................................................ 34
3.27. The Spectral Snapshots window ............................................................................................. 35
3.28. Show In pop-up .................................................................................................................... 35
3.29. Snapshot assigned to a Spectragraph ...................................................................................... 35
3.30. Selection for Snapshot Averaging ........................................................................................... 36
3.31. The Spectral Snapshots mini-menu ......................................................................................... 36
3.32. Average Snapshots Dialog ..................................................................................................... 36
3.33. Average appears in the Spectral Snapshots List ........................................................................ 37
3.34. The Transfer Function Snapshot Dialog ................................................................................... 37
3.35. Transfer Function Created From Two Spectral Snapshots ........................................................... 38
3.36. Spectragram (horizontal orientation) ....................................................................................... 39
3.37. Spectragram (vertical orientation) ........................................................................................... 39
3.38. Using the Spectragram and Spectragraph together .................................................................... 40
3.39. Spectragram preferences ........................................................................................................ 40
3.40. Power scaling set to logarithmic ............................................................................................. 41
3.41. Power scaling set to linear ..................................................................................................... 41
3.42. Triggering Oscilloscope ......................................................................................................... 41
3.43. Oscilloscope controls ............................................................................................................ 42
3.44. Oscilloscope running in dual-trace mode ................................................................................ 43
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SpectraFoo User's Guide
3.45. Oscilloscope Controls window ............................................................................................... 43
3.46. Power history ....................................................................................................................... 44
3.47. Envelope history ................................................................................................................... 44
3.48. Power Balance History .......................................................................................................... 45
3.49. Lissajous Phase Scope (vector mode) ...................................................................................... 45
3.50. Lissajous Phase Scope (X-Y mode) .......................................................................................... 45
3.51. Lissajous in Stereo Position Mode .......................................................................................... 46
3.52. Lissajous Control window ...................................................................................................... 46
3.53. Phase Torch™ ...................................................................................................................... 47
3.54. Phase Torch Control window ................................................................................................. 48
3.55. Phase Torch with threshold at -60 dB ..................................................................................... 48
3.56. Phase Torch Full Range ......................................................................................................... 49
3.57. Band Power History .............................................................................................................. 49
3.58. Band Power History controls ................................................................................................. 49
3.59. Vertical Correlation Meter ..................................................................................................... 50
3.60. Horizontal Correlation Meter ................................................................................................. 50
3.61. Correlation History ................................................................................................................ 50
3.62. Docked Correlation & History ................................................................................................ 50
3.63. 16 bit signal in the Code Meter ............................................................................................. 51
3.64. Definition of the offsets in the Bit Matrix ................................................................................. 51
3.65. Visual of the Bit Matrix ......................................................................................................... 51
3.66. Instantaneous Snapshot of Bit Matrix ...................................................................................... 52
3.67. Accumulation Snapshot of Bit Matrix ...................................................................................... 52
3.68. Bit Scope Layout with 512 Sample Time Slice and 8 Columns ................................................... 53
3.69. Bit Layout in Bit Scope ......................................................................................................... 53
3.70. THD Meter .......................................................................................................................... 53
3.71. Parameter control button ....................................................................................................... 54
4.1. SpectraFoo Signal Arrangement for MBM Transfer Function ........................................................ 55
4.2. Transfer Function of a Room Response with a time delay ........................................................... 56
4.3. Time Aligning the measurement with the Delay Finder Window .................................................. 57
4.4. Transfer Function after the measurement has been time-aligned .................................................. 58
4.5. Transfer Function Controls window .......................................................................................... 59
4.6. Power vs. Frequency ............................................................................................................... 60
4.7. Phase vs. Frequency ............................................................................................................... 61
4.8. Instrument Enable ................................................................................................................... 61
4.9. Solo button ............................................................................................................................ 61
4.10. Show Controls ...................................................................................................................... 61
4.11. Take Snapshot ...................................................................................................................... 61
4.12. Overlay List .......................................................................................................................... 61
4.13. Clear Data ........................................................................................................................... 62
4.14. Power Panel ......................................................................................................................... 62
4.15. Phase Panel .......................................................................................................................... 62
4.16. Simple Measurement setup .................................................................................................... 63
4.17. Setup for checking your D/A/D chain ..................................................................................... 64
4.18. Acoustic test setup ................................................................................................................ 64
4.19. Transfer function without delay compensation ......................................................................... 65
4.20. Transfer Function Controls Window ....................................................................................... 65
4.21. Delay Finder window ............................................................................................................ 66
4.22. Time-aligned transfer function ................................................................................................ 67
4.23. Coherence expressed mathematically ...................................................................................... 68
4.24. Simple source and response signals ........................................................................................ 68
4.25. Simple source – Complex response signal ............................................................................... 68
4.26. Acoustic test with reflected paths ........................................................................................... 69
4.27. Path length difference ........................................................................................................... 69
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SpectraFoo User's Guide
4.28. Null for frequencies .............................................................................................................. 69
4.29. Measurement and Correction setup ........................................................................................ 70
4.30. Transfer Function snapshot dialog .......................................................................................... 71
4.31. Transfer function Overlay List window .................................................................................... 72
4.32. Sample transfer function ........................................................................................................ 72
4.33. Transfer Function Snapshot Overlays window .......................................................................... 74
4.34. Transfer function snapshot edit dialog ..................................................................................... 74
4.35. Mini-menu window command pop-down menu ...................................................................... 75
5.1. Analyzer Control & Routing ..................................................................................................... 76
5.2. Master Controls window ......................................................................................................... 76
5.3. Instrument removal window .................................................................................................... 77
5.4. Channel assignment ................................................................................................................ 77
5.5. Analyzer Control & Routing Window ....................................................................................... 77
5.6. Analyzer channel routing ........................................................................................................ 78
5.7. Changing the number of analyzer channels ............................................................................... 79
5.8. Restart to reset analyzer channels ............................................................................................ 80
5.9. Changing the analysis depth .................................................................................................... 80
5.10. Analyzer channel names ....................................................................................................... 81
5.11. Named analyzer channels ..................................................................................................... 81
5.12. Channel names show in all instruments .................................................................................. 82
5.13. Sum/Difference pair modes menu ........................................................................................... 83
6.1. Level Calibration Dialog .......................................................................................................... 84
7.1. Accessing the library system from an instrument’s controls window ............................................. 85
7.2. Accessing the presets library pop-up from the controls button ..................................................... 86
7.3. Window Sets Dialog ............................................................................................................... 87
7.4. Grouping System .................................................................................................................... 87
7.5. Parameter Passing ................................................................................................................... 88
7.6. Link Groups Window .............................................................................................................. 88
7.7. Link Group Edit Window ........................................................................................................ 89
7.8. Groups pop-up Menu ............................................................................................................. 89
7.9. Selecting a group in the Groups Pop-up menu .......................................................................... 89
8.1. Signal Generator Control Window ........................................................................................... 90
8.2. Sine-Sweep Parameter Cluster .................................................................................................. 90
8.3. Sweep mode radio buttons ...................................................................................................... 91
8.4. White Noise Parameter Cluster ................................................................................................ 91
8.5. Pink Noise Parameter Cluster ................................................................................................... 92
8.6. Quantization and Dither controls ............................................................................................. 92
8.7. Dithered 16 bit signal ............................................................................................................. 93
8.8. Synchronization Controls ......................................................................................................... 93
8.9. Selecting the Rectangular window from the FFT Window library ................................................. 93
8.10. Bursting Controls .................................................................................................................. 94
8.11. 1 second of 125 ms bursts every 1/4 of a second ..................................................................... 94
8.12. 1 second of 125 ms windowed bursts every 1/4 of a second ..................................................... 94
8.13. Signal generator control cluster .............................................................................................. 95
9.1. FFT Window Control Window ................................................................................................. 96
10.1. Manual Capture Mode ............................................................................................................ 97
10.2. Level-based Capture Mode ..................................................................................................... 98
10.3. Level-based Capture envelope parameters ................................................................................ 98
10.4. Capture List Window .............................................................................................................. 99
10.5. The Capture Overview Window ............................................................................................ 100
10.6. Capture Overview Window: Top ........................................................................................... 100
10.7. Loop Start button ................................................................................................................. 101
10.8. Loop End button .................................................................................................................. 101
10.9. Capture Overview Window: Ribbons ..................................................................................... 101
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SpectraFoo User's Guide
10.10. Capture Overview Window: Bottom .................................................................................... 102
10.11. Stop .................................................................................................................................. 102
10.12. Play ................................................................................................................................... 102
10.13. Play From Beginning .......................................................................................................... 102
10.14. Playback mode .................................................................................................................. 102
10.15. Play Forward ...................................................................................................................... 102
10.16. Play Backward ................................................................................................................... 102
10.17. Loop Back and Forth .......................................................................................................... 102
10.18. Loop ................................................................................................................................. 102
10.19. Play Once Between Loop Points .......................................................................................... 102
10.20. Zoom Out ......................................................................................................................... 103
10.21. Zoom In ............................................................................................................................ 103
10.22. Cursor ............................................................................................................................... 103
10.23. Automation point movement tool ........................................................................................ 103
10.24. Automation point pencil tool ............................................................................................... 103
10.25. Automation mode ............................................................................................................... 103
10.26. Loop crossfade ................................................................................................................... 103
10.27. Numeric Time Selector Bar ................................................................................................. 103
10.28. Data slicing ....................................................................................................................... 104
11.1. Main Preferences ................................................................................................................ 105
11.2. Key Commands window ...................................................................................................... 107
11.3. Key Commands editor ......................................................................................................... 107
11.4. Hardware Configuration Window ......................................................................................... 108
183. One cycle ............................................................................................................................ 116
184. A linear trace ........................................................................................................................ 117
185. A logarithmic trace ................................................................................................................ 117
186. 0° Phase offset ...................................................................................................................... 118
187. 180° Phase offset .................................................................................................................. 118
188. Phase cancellation ................................................................................................................ 119
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List of Tables
3.1. Level Meter Options ................................................................................................................ 22
3.2. Trigger modes .......................................................................................................................... 42
11.1. Main Preferences .................................................................................................................. 105
10
1. Introduction
Congratulations!
You are now the owner of the most powerful audio analysis and metering system on the planet.
SpectraFoo is capable of monitoring up to 24 separate channels simultaneously (depending on your input
hardware). You may be asking – 24 channels all at once? How is this possible? The answer is that SpectraFoo
uses Metric Halo’s ultra efficient high-resolution analysis engine. This technology uses the power of your
Mac’s processor in conjunction with your audio hardware to provide blazingly fast and incredibly detailed
sample-accurate analysis and metering of any channel or an entire mix. SpectraFoo technology is unique
in its ability to provide you, the engineer, spectral, power, and phase analysis which is truly useful to your
production tasks.
About SpectraFoo Configurations
SpectraFoo is available in two configurations:
SpectraFoo Standard provides a comprehensive set of real-time metering instruments. For most mixing and
monitoring tasks, SpectraFoo Standard contains all the tools you will need. It gives you a comprehensive,
multi-channel view of signal levels, wave form data, signal histories, spectrum analysis and spectral histories,
and a variety of phase monitoring tools, including a lissajous phase scope, correlation metering, and the unique
Phase Torch™. It does not provide any of the deeper analysis tools found in SpectraFoo Complete.
SpectraFoo Complete provides all of the metering tools included in SpectraFoo Standard, but also includes
a number of additional features that allow more detailed analysis of audio signals and systems. SpectraFoo
Complete adds a multitone high-resolution sweeping signal generator, a recording, capture and static analysis
system, high-resolution bit-level metering facilities, and a detailed two-channel FFT transfer function measurement system, with support for Music Based Measurement, Time Delay Spectroscopy and multiple overlays
with coherence-based averaging. SpectraFoo Complete is a critical tool if you will be doing acoustical measurements, sound system or monitor tuning, musical instrument measurements, mastering, or any type of metering or measurement in which you need to be able to capture and strore the signals that you are measuring.
This manual documents both configurations of SpectraFoo, Standard and Complete. Features that are only
present in SpectraFoo Complete are notated with [SFC] at the beginning of the section that documents the
feature.
Metric Halo has a “no-penalty” upgrade policy for all software products. If you have purchased SpectraFoo
Standard and later decide that you need the power offered by SpectraFoo Complete, you can upgrade for the
difference between the suggested retail price of SpectraFoo Standard and SpectraFoo Complete at the time of
the upgrade. Contact Metric Halo directly at <sales@mhlabs.com> for more information.
Introduction
Welcome to the SpectraFoo Visual Audio Monitoring System – the world’s first audio analysis environment
that actually lets you see music. SpectraFoo is a high–precision, low–latency, fully realtime audio visualization
and analysis system.
SpectraFoo takes advantage of the phenomenon known as synesthesia. The word synesthesia, meaning “joined
sensation,” denotes the rare capacity to see sounds, taste shapes, or experience other equally startling sensory
blendings whose quality seems difficult for most of us to imagine. Very few people experience natural synesthesia. Those who do usually possess distinct cognitive advantages over the rest of us. For example, many
people with perfect pitch associate particular pitches with particular colors. They see sound as well as hear it.
The interaction of vision and hearing helps these people maintain an absolute point of reference with regard
to pitch. This allows them to discern absolute pitch values without the need for a reference tone. SpectraFoo
allows anyone to experience the benefits of synesthetic sensation.
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Introduction
In order for the human brain to properly integrate multiple sensory inputs and derive greater value from them,
the inputs must be truly synchronized. SpectraFoo is the first audio visualization system to provide high resolution spectral and phase information that is fluidly animated and absolutely synchronized to the live audio
signal. It is the first audio analyzer anywhere to allow the user to tap into the power of synesthesia.
Like many other audio analyzers, SpectraFoo’s analysis engine is based on the Fast Fourier Transform (FFT).
The FFT algorithm is an efficient means of computing a Fourier Transform on a computer. The Fourier transform
was developed between 1804–1807 by the mathematician Joseph Fourier as part of a study of heat transfer. The
Fourier transform converts a continuous record of amplitude vs. time into a record of amplitude vs. frequency.
A modification of the Fourier Transform called the Discrete Fourier Transform (DFT) was developed to deal
with sampled rather than continuous waveforms. The FFT algorithm was developed as an efficient way of
computing the DFT on digital computers.
FFT-based analysis facilitates highly precise measurements. As a result, it has become a natural choice for
audio analysis systems. Unfortunately, FFT-based methods have historically been more suited to Electrical
Engineering-type audio measurements than dynamic measurements of musical program material.
A traditional technique is to subject the system being measured to a known, controlled test signal. In order to
get high-resolution measurements from the analyzer, one must wait for a significant period of time while the
output of the system is captured by the analyzer and then transformed. If you want to measure the average
response of the system, you have to wait for the analyzer to make many captures, transform them and average
them before you see the results.
With traditional transformation algorithms, the rate at which the signal is transformed is constrained by the
spacing of the spectral lines. As a result, many professionals who work in the creative side of audio have
resorted to using low-resolution RTA-type analyzers to get real-time information. SpectraFoo utilizes patent
pending technology to decouple the transformation resolution from the transformation rate. As a result, SpectraFoo is fast, fast, fast! It can perform multichannel FFTs up to 60 times a second, allowing you to see spectral
features as small as 2/3 Hz wide while staying absolutely synchronized with the source material. This allows
you to experience and analyze sonic events simultaneously!
In addition to its unmatched realtime performance, SpectraFoo also provides a full suite of highly precise
quantitative analysis tools, including a capture and storage system which is seamlessly integrated into the
monitoring environment. All of the intuitive knowledge you have gained via synesthesia can be leveraged on
top of the quantitative measurements that SpectraFoo provides.
The following is a guide that provides an overview of SpectraFoo’s features and capabilities. This guide assumes
that you have a basic working knowledge of the Mac OS and its standard techniques. If you are new to Mac
OS X, you should consult your Apple documentation before continuing.
System Requirements
• A Macintosh computer running Mac OS X 10.4.11 or newer – We generally recommend that you use
the latest available version of the OS. If you are using one of the previous releases (10.4 or 10.5), we
recommend that you updated to Apple’s final System Update for that release; Metric Halo only tests
SpectraFoo with the final System Update of previous OS releases.
• RAM – while SpectraFoo is completely compatible with OS X virtual memory, like all media applications, it benefits from more available physical memory. As a practical rule of thumb, all OS X systems
ought to have at least 2 GB of physical memory installed (4 GB or more preferred). If you plan on using
the capture engine or the delay finder, you will benefit from having more physical RAM installed, but
it is not required for correct operation.
• OpenGL – SpectraFoo can optionally take advantage of OpenGL acceleration to increase performance,
reduce system loading and reduce the likelihood of the fan turning on when used on a laptop. In order
for SpectraFoo to use OpenGL, your system must be capable of supporting Apple’s Quartz Extreme
technology. All shipping Macs support this technology, and this has been the case for a number of years
12
Introduction
(at the time of this writing). If you have a very old Mac, it may not support Quartz Extreme, and if this is
the case, you will not be able to take advantage of the OpenGL optimizations available in SpectraFoo.
• A CoreAudio compliant audio I/O device – Many USB devices (including the Macintosh Built In Audio)
are implemented as two separate devices: one CoreAudio device for input and one for output. You will
need to create an Aggregate Device in the Audio Midi Setup utility to configure multiple CoreAudio
devices to appear to SpectraFoo (and all other CoreAudio clients) as a single unified device.
SpectraFoo’s physical I/O capability and supported sample rates are controlled by the audio hardware
you choose to use with SpectraFoo. For best results, and the highest degree of compatibility testing outof-the-box, we recommend that you use a member of Metric Halo’s Mobile I/O Family of Firewire audio
interfaces.
13
2. SpectraFoo Basics
Getting to know SpectraFoo
SpectraFoo provides you with a wide variety of audio monitoring and analysis instruments.You may access
any combination of the instruments at any time. This allows you to use as much or as little analysis as you
want. The following section describes the instruments available to you and how they work. Please refer to the
Section on Control and Routing to learn how to control the flow of signal through SpectraFoo.
Common Features – Instruments
All of the instruments have the following controls:
• A power button
Figure 2.1: Power button
• A solo button
Figure 2.2: Solo button
• A parameter control button
Figure 2.3: Parameter control button
The power button, when turned off, disables the instrument. The solo button works much like the solo button
on a recording console in that it shuts off all of the other instruments. However, if more than one instrument
is in solo mode, all of the soloed instruments will continue to run, while the un–soloed instruments will be
disabled. If an instrument is in solo mode and turned off, it will be disabled, as will all of the un–soloed
instruments. These controls are provided to allow you to focus your attention on measurements made by a
subset of SpectraFoo’s instruments.
Although SpectraFoo is always analyzing the signal in real–time, limitations in the drawing speed of the host
computer can cause the display to slow down when many instruments are enabled. By soloing the instruments
that you are specifically interested in at a given point in time, you will improve real–time performance of the
display. For faster host machines, the difference in graphics performance will be less noticeable.
When the parameter control button is clicked, it opens a floating window which allows you to control, in
real–time, many of the display parameters for the instrument in question. These control windows will be
described in more detail below.
Some of the instruments have additional controls when they are in the consolidated Real Time Rack window.
These controls provide “hardwired” linking functionality for the instruments. The controls for the real-time
rack instruments are illustrated and described in the picture below:
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SpectraFoo Basics
Power Button : turns an instrument on and off
Solo: Shuts off all other instruments
Show Details: Indicates that the instrument has
adjustable display parameters and/or detailed numerical readings. Clicking this button will bring up a
window that will display these items.
Stereo Link: Allows you to link the parameters settings for the
left and right channels of a particular instrument.
Link: Allows you to link the display parameters of
the Spectragraph and Spectragram for a given
channel.
Figure 2.4: Real Time Rack Control buttons
Common Features – Control Windows
As with the instruments themselves, the control windows for the instruments also contain some common
features.
• The control window for each instrument contains one or more Active Channel pop-up menus. These
allow you to select which analyzer channel is routed into the instrument for display (for instruments that
only meter one channel at at time). For stereo instruments, there will be more than one Active Channel
pop-up menu – one for each channel that can be routed into the instrument, and generally labelled
“Channel 1” and “Channel 2”.
Figure 2.5: Active Channel pop-up menu (with custom channel names)
• The control window for each instrument also contains the parameter library pop-up menu (in the upper
left-hand corner). This pop-up provides access to an integrated library system. You can use it to save
and recall snapshots of the instrument’s configuration. All the snapshots you create are available to
instruments of the same type, and are maintained between each use of SpectraFoo.
• The control window for each instrument also contains the “Groups” pop-up meu (in the upper righthand corner). The Groups pop-up menu provides access to a flexible parameter linking system. The
items listed in the menu are the names of parameter groups. By selecting one or more groups, you add
the instrument to one or more parameter group. Each parameter group will automatically broadcast
all parameter changes from any member of the group to all the members of the group. By configuring
your parameter groups and adding various instruments to the groups, you can keep the state of multiple
instruments synchronized as you change the configurations of the instruments. One of the really cool
features of parameter groups is that they allow you to link between instruments of different types. For
example you can link the frequency controls between Spectragrams and Spectragraphs.
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SpectraFoo Basics
For the real-time rack window, you have an additional way of controlling the enable and solo states of the
instruments in the rack. You can set up predefined groups of enabled instruments using the commands found in
the group menu. This allows you to quickly and easily “switch modes” as far as where your attention is focussed.
These instrument groups only effect instruments in the consolidated Real Time Rack view described below.
Even though these are called “Instrument Groups” they have no connection to the Link Groups described
above.
Figure 2.6: Instrument Groups Menu – Only applies to instruments in the Real Time Rack
• Add to Group Library… Takes a snapshot of all of the current settings of the power and solo buttons. A
dialog box will appear allowing you to name the group. When you name the configuration, you may
use the slash key (/) followed by the character of your choice to create a command key to recall the
group. For example, you have a group you want to name MyScene. If you type My Scene/0 as the name,
you may recall this configuration by pressing Command-0.
• Delete from Group Library… Deletes a group from the menu. A dialog box will appear with a pop-up
menu that contains all of your currently saved groups. Select the group that you wish to delete from the
menu. Click OK to delete - click cancel to abort the delete operation.
• Group Library entries: These items make up the Group library. Items can be added to or deleted from
the library at any time.
The Real Time Rack
SpectraFoo provides a two-channel consolidated “Real Time Rack” view that contains all of the instruments
in one convenient window. When you use this view, the Spectragram, Spectragraph and Oscilloscope instruments have linking buttons that allow you to either stereo link the control parameters between the left and
right channel instruments, or to link the control parameters of the Spectragram and Spectragraph of the same
channel. These linking buttons are very similar in concept to the link feature that appears on good-quality
stereo compressors. For example, the stereo link button on the Spectragraph allows you to ensure that both
the left and right channel Spectragraph instruments use the same frequency calibration. When instruments are
stereo linked, the parameters for both channels can be controlled from either the left or right channel details
window. These linking features are currently only available in the Real Time Rack consolidated view. For
the individual instruments available from the Master Controls window, you can use the Link Group system
described on the previous page for linking instruments.
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SpectraFoo Basics
Timecode Clock
Digital Level Meters
L/R Balance Meter
Left Channel Oscilloscope
Left Channel Spectragram
Left Channel Spectragraph
Right Channel Spectragraph
Right Channel Spectragram
Left Channel Power History Meter
Lissajous Phase Scope
Left Channel Envelope Display
Phase Torch™ Band Limited Phase Meter
Right Channel Envelope History
Right Channel Power History Meter
Right Channel Oscilloscope
Figure 2.7: Real Time Rack
Real Time Rack Consolidated View
You may move instruments within the rack by clicking on the instrument you want to move and dragging it
to a new location. As you drag the instrument around, the rack will indicate places to which the instrument
can be moved by drawing a heavy border around the empty spot. If you release the mouse button while the
instrument is over a location that is already occupied, the instrument will automatically return to its original
location. Moving an instrument within the rack does not interrupt the analysis process or even the display
update. In fact, whenever you turn a knob or move a fader in SpectraFoo, everything responds instantaneously.
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3. Instruments
SpectraFoo Standard
SpectraFoo Standard includes the following set of real time metering instruments:
• Level Meters: high resolution, standards-based level metering with the ability to display Peak, RMS and
VU levels simultaneously. Supports European and AES PPM standards and K-System metering. Highly
user configurable.
• Spectragraph: ultra high resolution real-time two channel spectrum analyzer with snapshots, cursors
and overlays. Supports a variety of scaling, spectral weighting and ballistics.
• Spectragram: history display to accompany Spectragraph. Like a topological map of your signal; beautiful & informative!
• Timecode clock: running display of current timecode source.
• Oscilloscope: configurable, triggerable, dual channel audio frequency oscilloscope. Provides high-resolution wave form display and simple waveform math. Versatile triggering modes make this ideal for
a variety of measurements.
• Power History: shows a running history of the peak and RMS level of the metered signal.
• Envelope History: shows running “envelope” of the metered signal, similar to a DAW overview.
• Band Power History: shows the running history of the total power within a specified bandwidth around
a specified center frequency.
• Phase Torch™: Metric Halo’s unique two-channel phase visualization tool, displaying phase as a function of frequency, independent of power.
• Lissajous Phase Meter: familiar X-Y mode O-scope two channel phase meter – with a twist; supports XY mode, Lissajous mode, and Stereo position mode. Also supports auto gain control to provide useful
readings during fades or other very low-level material.
• Power Balance: unique meter that shows the history of the relative power between two channels. Perfect
for balancing mics or for monitoring the relative stereo soundfield balance.
• Correlation: A favorite in European broadcast circles; shows an instantaneous representation of how
mono-compatible the monitored stereo signal is.
• Correlation History: a companion to the Correlation meter, the Correlation History meter shows how
the correlation is changing over time. Dockable with the Correlation meter.
SpectraFoo Complete
SpectraFoo Complete adds the following instruments to the Standard set:
• Code Meter: Shows the per-bit activity of the digital audio signal routed to the meter; commonly known
as a “Bit-Scope”.
• Code Matrix Meter: A unique meter designed to examine the upper 16 bits of a digital signal. Allows
you to quickly discover missing codes, converter problems and code-space utilization.
• Code List Meter: A 1630-style display that shows the sequence of code values in the digital signal routed
to the meter.
• Transfer Function: Two channel differential FFT analyzer. This instrument allows you to compare the
spectral and phase content of two signals. If the two signals are related (part of a system), the Transfer
Function allows you to quickly discern the effect that the system has on the signals. Coupled with the
delay finder (see below), this is the critical tool for measuring the acoustic response of speakers and
rooms. It is also the primary tool for measuring the electrical response of signal processors. You can also
use the transfer function to analyze the difference between snapshots captured with the Spectragraph
instrument.
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• Delay Finder: This instrument is used to measure the delay between the two analyzer channels used by
the Transfer Function. It does this by computing the impulse response of the linear transfer function that
relates the response channel to the source channel. After computing the impulse response, the delay
finder automatically compensates for the delay by inserting additional delay internally on the source
channel so that both channels line up. You can use the delay finder tool to choose a different alignment
delay.
• THD Meter: This instrument provides S/N and THD measurements.
These instruments are discussed in detail on the following pages. This instrument reference section details the
appearance and function of the instruments, as well as the controllable parameters that you can use to adjust
the functions of the instruments.
Level Meter
Overview
This instrument provides a highly configurable two-channel, three–in–one digital level meter. Like all SpectraFoo instruments, the level meters are resizable. If you make the meter wider than it is tall, it will use a
horizontal orientation.
Figure 3.1: Level Meter Horizontal Orientation
If you make it taller than it is wide, the meter will use a vertical orientation.
Figure 3.2: Level Meter Vertical Orientation
SpectraFoo’s Level Meters allow you to switch on the fly between modern, fast tracking, sample accurate
digital ballistics and traditional standards–based PPM ballistics. Many engineers are used to working with PPM
standard hardware level meters and SpectraFoo can emulate standard PPM ballistics, but it can also do much
more. The ballistics for both the Peak crawlback and VU level is fully configurable.
The meter can show you the Peak, RMS and VU levels along with holds for Peak and RMS simultaneously.
The meter also has two available color modes:
• The Level based color mode colors the meter bars based upon the the level of the signal. The color
breakpoints are user configurable and can be adjusted to provide smooth transitions or hard edges. This
mode is the standard configuration for the meters, and is required to implement the K-System calibrated
meters.
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Click this button to pop up the Power Meter Details window
These provide instantaneous numerical readings of the
Peak , RMS, and VU levels with 0.01 dB accuracy.
Click this button to pop up the
Power Meter Options window
Clicking this button resets the
Peak and RMS Peak Holds.
• The second color mode causes the meter bar to be color coded to indicate Peak and RMS, and uses
color to distinguish its different modes. The yellow part of the meter indicates the instantaneous peak to
peak level of the program material. The purple part of the meter indicates the RMS level. These colors
are user definable.
The Peak and RMS meters each have independent, resettable peak hold functions. The peak holds are represented by triangular carets of the same color as the meter to which they correlate. The hold indicators can
also be drawn as bars. The VU meter is an adjustable ballistic average indicator that is represented by the grey
triangular carets (or bar if selected). Detailed meter readings (1/100 dB accuracy) and meter control parameters
can be accessed by clicking on the Show Details button. The meter also contains a numerical counter that
indicates the largest number of consecutive samples surpassing 0 dBFS, as well as the number of times the
input signal has exceeded the clip threshold. The calibration of the meters is referenced against 0 dBFS, unless
you have selected one of the dBu calibrated meter scales.
User-Definable Over (Digital Clip) Counter
The Level Meter counts consecutive full scale samples and displays the largest count encountered. This is
displayed in the field labeled “cfs”. You can also define how many consecutive full scale samples the Level
Meter has to see before it considers the signal to have clipped. You control this behavior using the Physical
Unit calibration system in SpectraFoo (see “Physical Unit Calibration In SpectraFoo”). The Level Meter has
Figure 3.3: Digital Level Meters (Peak, RMS and VU meters w/ Clipped Sample Counter)
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a numerical counter which keeps track of the number of “overs” which have occurred. This is displayed in
the field labeled “cnt”.
Figure 3.4: Over Counter
The true flexibility of the meters is controlled using the Level Meter Controls window. Click the Meter’s parameter control button to display the Level Meter Controls window:
Figure 3.5: Level Meter Controls Window
Sum & Difference Meter Mode
The Level meters provide a Sum & Difference mode that shows L+R and L-R metering. When the Sum &
Difference mode is selected, the left bar is the sum and the right bar is the difference (if the meter is in the
vertical orientation; if the meter is horizontal the sum is in the top bar and the difference is in the bottom bar).
The level meter mode is selected with the Meter Mode pop-up menu which allows you to configure a meter
to run as a straight level meter or as a Sum & Difference meter.
Detailed Readout and Hold Indicator Controls
The Level Meter Controls window also contains detailed numerical readouts for the Peak, RMS and VU levels
for each channel. Next to the labels for the readouts, there are checkbox controls. These controls allow you
to determine whether or not to display the associated hold indicators on the meters.
Options Window
The rest of the meter configuration controls are in a second control window called the Level Meter Options
window. You access this window by clicking the Options… button at the bottom of the Controls window.
Clicking the Options… button brings up the Level Meter Options window:
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Figure 3.6: Level Meter Options Window
The table below describes the controls which are available in the Level Meter Options window.
Table3.1.Level Meter Options
Control What It Does
VU Settling Time slider Controls the settling time of the VU indicator. When
the slider is set on the VU mark, the indicator will
use VU ballistics. This parameter is global for all
channels and meters in the system.
PPM Settling Time slider Controls the settling time of the level meter when
Use PPM ballistics is checked. This parameter is
global for all channels and meters in the system.
Peak Float Size slider Controls the size of the floating peak indicators.
PPM Hold Release Time slider Sets the amount of time the Peak Holds wait before
resetting when Auto-Release Holds is checked.
Meter Scaling slider Sets the dynamic range of the Level Meter.
Tick Spacing slider Sets the calibration mark spacing of the meter when
the SpectraFoo scale is selected
Scale Type pop-up menu Selects the PPM standard to use for the meter scale.
Use Level Based Color checkbox Activates level based transition colors for the meters.
When this checkbox is unchecked, meters use original SpectraFoo color coding for Peak and RMS levels.
Use PPM Ballistics checkbox Activates PPM decay for the meter. If this is
unchecked, the meter will use the original “instantaneous” SpectraFoo ballistics.
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Control What It Does
Draw VU as Solid Bar When unchecked, the white tick shows the VU lev-
el and RMS is shown as the solid bar in the meter.
When checked, the solid bar shows the VU level and
the white tick shows RMS. This allows you to create
a bar meter which uses VU ballistics.
Use AES Std. RMS Ref When checked, this will adjust the RMS level by
+3.01 dB to match the AES recommended specification. Regardless of how this parameter is set, it must
be set before calibrating your analyzer.
Draw Peak Level as Bar checkbox When checked, the Level Meter will display the Peak
and RMS levels as one continuous bar (as in previous
versions of SpectraFoo). When unchecked, the Peak
level will be displayed as a separate indicator which
floats above the RMS bar. Useful for creating meters
that read peak-only.
Draw Holds as Arrows checkbox When checked, Peak holds will be displayed as ar-
rows (like previous versions of SpectraFoo). When
unchecked Peak Holds will be displayed as lines.
Auto Release Holds checkbox When checked, the Peak Holds will reset after the
amount of time you specify using the PPM Hold Re-
lease Time slider.
Use Solid Color Transitions When checked, the meters will show a "hard" tran-
sition from one color to the next; this is commonly
used for K meters. When unchecked, the color transitions fade, from one to the next.
Color Transition sliders The Safe Until, Caution Level and Danger Level slid-
ers set the dbFS level at which color transitions will
occur. In the figure above, a signal will be displayed
as green until -30 db, turn yellow from -30 to -18 dB
and is red over -18 dB. You may change the colors
by clicking the color wells at the left end of the sliders.
Peak, RMS, VU color wells These allow you to set the colors for the Peak, RMS
and VU indicators.
PPM ballistics
The Level Meter can be set to use PPM decay or to provide instantaneous digital metering with no crawlback.
In order to operate as a traditional Peak Program Meter, you must configure the meters to use PPM ballistics
and choose the standard crawlback speed. This is the default configuration for the meters. You can also choose
non-standard crawlback speeds to make the meters more responsive or to provide a longer persistance time;
choose the settings that work best for you.
To configure a Level Meter to use PPM ballistics:
1. Open the Level Meter controls window and click the Options… button. The Level Meter Options win-
dow will appear:
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Figure 3.7: Level Meter Options Window
2. Check Use PPM Ballistics. The meter will now use the standard PPM decay time. You can change the
decay time using the PPM Settling Time slider.
Meter scales
SpectraFoo now has a variety of User Selectable scale calibrations. In addition to the equally spaced level
calibration (aptly called the SpectraFoo Calibration), you can choose from the following international PPM
and VU standards:
1. UK PPM – UK Standard 1-7 Scale. Line-up calibration is 0 dBu for marking “4”.
2. EBU PPM – EBU Standard PPM Scale. Line-up calibration is 0 dBu at marking “Test”.
3. IEEE PPM – IEEE Standard PPM Scale. Line-up calibration is 0 dBu at marking “Test”.
4. IEEE VU – IEEE Standard VU Scale. Line-up calibration is +4 dBu at marking “0”.
5. DIN PPM – DIN Standard PPM Scale. Line-up calibration is +6 dBu at marking “0”.
6. Nordic PPM – Nordic Standard PPM Scale. Line-up calibration is +6 dBu at marking “Test”.
7. Digital PPM – Digital PPM Scale. Line-up calibration is 0 dBFS at marking “0”.
8. SpectraFoo – dBu calibrated scale with even spacing of calibration marks.
The PPM crawlback ballistics in the meters conform to a crawlback rate of 20 dB in 1.7 seconds. Fast PPM
can be accomplished by setting the PPM settling time to 0.85 seconds.
User selectable meter bar colors
SpectraFoo has two different ways of color-coding its meters. The first method, which corresponds to the
original SpectraFoo color scheme, provides one color for peak-level and another for RMS level. The second
method, called level-based color, changes the color of the meter bar based on the level of the audio. You can
change the colors in both of the color-coding methods from within the Level Meters Options window.
To change the Peak and RMS and VU colors for a meter:
1. If the Meter’s Control window is not visible, show the Control window by clicking the Show Controls
button, and then selecting the “Options” button at the bottom of the Controls window.
2. Click the appropriate color tile within the Controls Window. The Macintosh Color Picker dialog will
appear.
3. Select the new color in the dialog.
4. The Peak, RMS, and VU colors are used for the Peak, RMS, and VU holds respectively. If Use Level Based
Color is unchecked the Peak and RMS colors are used for the Peak and RMS meter bars, respectively.
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To change the Level-based Colors:
1. If the Meter’s Control window is not visible, show the Control window by clicking the Show Controls
button, and then selecting the “Options” button at the bottom of the Controls window.
2. Click the appropriate color tile within the Controls Window. The Macintosh Color Picker dialog will
appear. The three Level-based color tiles correspond to the “Safe” color, the “Caution” color, and the
“Danger” color respectively. These colors also correspond to low, medium, and high levels. The standard configuration of these colors is Safe=Green, Caution=Yellow, Danger=Red.
Meter bar color transition levels
The level-based color coding scheme assigns colors to the meter bars based on the corresponding level of the
signal at each point along the bar. The colors are taken from the level based colors as described above. The
transition points, e.g. levels at which the color changes from Safe to Caution and from Caution to Danger,
are user selectable. This allows you to set the points at which the color bar changes to match your needs and
expectations.
To change the transition levels:
1. If the Meter’s Control window is not visible, show the Control window by clicking the Show Controls
button, and then select the “Options” button.
2. Adjust the appropriate Level Slider in the bottom of the control window.
3. The Danger level slider controls the level at which the meter bar is completely at the Danger color.
4. The Caution level slider controls the level at which the meter bar is completely set to the Caution color.
5. The Safe Until level slider controls the level below which the meter bar is completely set to the Safe
color. The meter bar is displayed in the Safe color from –∞ to the Safe Until level.
Spectragraph
Overview
The spectrum analysis within SpectraFoo utilizes a multichannel, high resolution, real–time FFT engine. At
its highest resolution setting, SpectraFoo utilizes 64k point FFTs, allowing you to see features with widths as
small as 2/3 Hz. SpectraFoo creates a new analysis up to 60 times per second, allowing you to see musical
structure even at the highest tempos.
Although the Spectragraph excels at traditional applications such as analyzing the distortion characteristics of
audio equipment, its true strength lies in its sheer speed. SpectraFoo’s Spectragraph is fast enough to create a
highly detailed, animated “movie” of sonic events. If you have been watching SpectraFoo monitor a favorite
album of yours while reading this guide, you probably have already noticed this.
Because the Spectragraph is so completely synchronized with the material it is monitoring, the information it
displays can be experienced in a sensory rather than intellectual way – much the same way as you experience
music itself. The key to making the most out of the Spectragraph (as well as all of the other instruments) is
to spend some time listening to and looking at your favorite music – music that you know really well. After
a relatively short amount of time, details of the recordings such as phase structure, overall spectral balance,
dynamic range, frequency range, and low frequency roll-off will literally leap out at you. You will be experiencing, rather than thinking about, quantitative analysis.
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Instruments
Peak Hold Trace: Displays the maximum
amplitude per frequency bin since the
peak hold was last reset. To reset the
peak hold either click on the instrument
itself or click on Reset Peak Holds in the
details window.
Instantaneous Trace: Displays the current
level of the signal at each frequency.
AverageTrace: Displays the average
level of the signal at each frequency.
These checkboxes show and hide
the traces, allowing you to focus
your attention on any combination
of traces.
Click to reset the peak trace.
Sets the averaging rate for the
average trace. When you move
this slider, the ballistics of the
average trace will change in
realtime.
Gives a precise numerical reading of the
settling time of the average trace.
Use these sliders to change the low
and high frequency limits that the
Spectragraph applies to its display.
This lets you zoom in on a particular
frequency range. As you change
the low and high frequency limits,
the frequency calibration on the
bottom of the Spectragraph will
instantly rescale itself.
Use these sliders to change the low and high power limits that the Spectragraph applies to its display.
This lets you zoom in on a particular power range. As you change the low and high frequency limits,
the power calibration on the left side of the spectragraph will instantly rescale itself.
The Frequency Scaling and Power
Scaling sliders allow you to adjust the
scaling of the frequency and power
calibrations. When the slider is set to its
far left limit, the scale is roughly linear.
When the slider is set to its right limit,
the scale is logarithmic. The best way to
get a feel for scaling, is to simply grab a
slider and mov e it back and forth.The
frequency and power calibrations will
track your movements in realtime and
useful scaling settings will quickly
become obvious.
Figure 3.8: The Spectragraph and controls
The Spectragraph utilizes a triple display for each input channel. The bright green trace provides instantaneous
spectral analysis. The purple trace shows the average spectral content referenced over a user specified length
of time; this is controlled from the Details window. The dark green trace represents the peak spectral power
monitored since the peak was last reset. Using the Details window, you can alter the Spectragraph’s frequency
and power scaling as well as its averaging characteristics in realtime. This allows you to easily focus on very
fine details. In addition, the Control window allows you to adjust the colors assigned to each trace.
Dual channel modes
The Spectragraph can run as a 6 trace, dual channel instrument, allowing you to route any two channels to
one Spectragraph window. For example, you could route the left and right channels of a stereo pair into a
Spectragraph.
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Instruments
Figure 3.9: Spectragraph showing the left and right channels of a stereo pair
You can also route two different instruments such as a kick drum and a bass to a Spectragraph and do a live
comparison between them.
To display a second trace in a Spectragraph:
1. Select the two channels that you wish to display using the channel pop-ups in the controls window.
2. Select the mode of the second trace using the second traces pop-up. If the mode of the second trace is set
to None, the Spectragraph will only display channel 1.
Sum, Multiply and Overlap modes
You use the Spectragraph Controls window to display and control second traces. The second trace in a dual
trace Spectragraph can represent the second input channel as in the examples above, or one may be set to
one of the following:
• None: This does not draw a second trace.
• Channel 2: This draws the Channel 2 selection as the second trace.
• 1+2: The sum of the two channels routed to the Spectragraph. This shows the sum total power in the
stereo signal.
• (1+2)-3 dB: The sum of the two channels routed to the Spectragraph -3 dB. This shows the average total
power in the stereo signal.
• 1*2: The product of the two channels routed to the Spectragraph. This filters the power of one signal
with the power of the other.
• sqrt(1*2): The square root of the product of the two channels routed to the Spectragraph. This shows
the overlap of the power in the two signals.
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Instruments
Figure 3.10: Spectragraph Second Traces pop-up
Accumulation modes
SpectraFoo’s underlying FFT generates more data than can be displayed on screen at once. The way that this
data is treated when the system computes the trace is called the accumulation mode. SpectraFoo provides two
accumulation modes that you can choose using the Spectragraph Controls window:
Figure 3.11: Accumulation Mode pop-up
1. When the Accumulation Mode is set to White Noise is Flat, the Spectragraph shows the maximum
power of all of the spectral lines in the FFT that fit into each point in the displayed trace. This has the
effect displaying white noise (or noise that has an equal amount of power at each frequency) as a flat
line. This mode is traditionally used when the frequency scale of the graph is linear.
2. When the Accumulation Mode is set to Pink Noise is Flat, the Spectragraph shows the sum of the power
of all of the spectral lines in the FFT that fit into each point in the displayed trace. This has the effect of
displaying pink noise (or noise that has an equal amount of power in each octave) as a flat line. This
mode is traditionally used when the frequency scale of the graph is logarithmic and corresponds to the
type of display available on a traditional RTA.
The figures below show the results of the two weighting accumulation modes with the two different kinds
of noise.
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Instruments
Figure 3.12: Pink Noise with Pink is Flat
Figure 3.13: Pink Noise with White is Flat
Figure 3.14: White Noise with Pink is Flat
Figure 3.15: White Noise with White is Flat
Physical unit calibration
SpectraFoo can be globally calibrated to Physical Units (i.e. dBu, dBV). You can use dBu units in the power
calibration for the Spectragraph by checking the Use dBu Calib checkbox in the instrument’s Spectragraph
Control window. See “Physical Unit Calibration In SpectraFoo” for more information about physical unit calibration in SpectraFoo.
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Trace colors
The traces in the Spectragraph can be set to any color supported by your Mac.
To change the color of a trace in the Spectragraph:
1. Click on the colored well to the left of the trace visibility check box in the Spectragraph Controls
window.
Figure 3.16: Accessing Trace Color controls
The Macintosh Color Picker will appear.
Figure 3.17: The Mac OS color picker
2. Choose the color you want, and click OK. The trace will now appear in the color you selected.
Octave Analysis
The Spectragraph includes octave modes which allow you to display frequency data in resolutions ranging
from 1 octave to Continuous.
You use the Resolution pop-up in the Spectragraph Controls window to set the display resolution.
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