Sabine Welder SDA-102 User Manual
SDA-102
www.Sabine.com
Front Panel
OPERATING
GUIDE
INSIDE THIS GUIDE:
SDA-102 Controls 2
Digital Delay Advantage 3-6
Delay Applications 6-8
Calculating Delay Time 9
Basic Operating Instructions 9
Engineering Specifications 10
FCC Information 10
Safety Information 11
Warranty 12
SDA-102
Back Panel
CONGRATULATIONS! You have chosen the ultimate digital delay for acoustical
alignment of speaker systems in auditoriums, churches, stadiums, theaters, conference rooms, and venues of all sizes and designs. For an explanation of the digital
delay solution and advantage, see page 3. For the delay application guide, turn to
page 6.
Special features of the SDA-102 Instant Delay:
• One input, two outputs
• 20-bit A/D & D/A converters with 24-bit digital processing
• Up to 999.98 millisecond delay
• 20 microsecond resolution
• Input and output level controls
• Front panel lockout
• Optional rack tray holds up to six units
MADE IN USA. © 1997 Sabine Inc.
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SDA-102 Front & Back Panels
POWER
The ON/OFF power switch is a two-position push button switch.
The LED display illuminates on power-up.
ACTIVE/BYPASS
In Active mode, the unit delays the input signal. When the
BYPASS button is depressed, the unit is in Bypass mode. If the
unit is turned off, it must be in Bypass to pass audio.
INPUT LEVEL CLIP INDICATOR
The red clip LED comes on when the input level is 6dB below
clipping level. Adjust the clip IN so that the SDA's red clip LED
blinks intermittently during maximum program levels. Higher
levels cause clipping and distortion, and lower levels introduce
noise.
SIGNAL INDICATOR
The SIGNAL LED lights when the signal level is above -30dB of
clip level.
LEVEL IN
Use a small flathead screwdriver to increase or decrease the
input level.
LEVEL OUT A/B
The output level for channels A and B can be adjusted
individually. Use a screwdriver to increase or decrease the
output level for either channel. The output level is adjustable
from 0 to 100%. Full output level is +26dBV into 600 Ohms,
balanced. Peak output capability is +29dBV peak, balanced.
FRONT PANEL LOCKOUT SWITCH
The unmarked switch at the upper left of the back panel is the
front panel lockout switch. When in the UP position, the unit is
unlocked (default) and anyone can adjust the SDA's controls.
When the switch is in the DOWN position, the unit is locked,
and the delay time can't be changed.
12VDC ADAPTOR
The SDA external power supply is included with the unit. Use
of any other power supplies may cause fire, injury or permanent damage to the unit and WILL VOID THE WARRANTY.
INPUT/OUTPUT CONNECTORS
The SDA includes three Euroblock three-pin connectors. The
numbers 3-2-1 marked above the connectors refer to LOW (3) HIGH (2) - SHIELD (1).
A/B SELECT & CHANNEL INDICATORS
This push button allows you to set delay time for channels A and
B separately. Select a channel using the A/B button, and the
corresponding channel indicator LED will light red. Then use
the arrow keys to adjust the delay time for that channel.
UP/DOWN ARROWS
Use the arrow keys to increase or decrease delay time (in
milliseconds) for either channel individually.
LED DISPLAY
The four-digit LED display shows delay time in milliseconds.
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THE DIGITAL DELAY ADVANTAGE: Synchronize loudspeakers,
eliminate comb filter distortion, align the acoustic image
Why Digital Delays?
The most intelligible sound occurs when two people speak face to face. The sound is loud
and dry and the direction of the sound aligns with the speaker. It stands to reason that the
most intelligible sound systems are the ones that come closest to emulating face to face
communication. If this is your goal, a digital delay is essential to your sound system.
Until recently, a digital delay’s cost was prohibitive for the average user. Only high-end
applications could justify the cost. But recent drops in component prices now put the benefits
of digital delays within affordable reach of every user.
There are three distinct applications for digital delays. The first and most important is
synchronization of the loudspeakers to control excess reverberation and echo. Secondly,
digital delays help control comb filter distortion, and finally, digital delays are useful for
aligning the acoustic image so the direction of the sound seems to be coming from the
performer rather than the loudspeaker.
This manual goes beyond the typical operating guide that only explains the front and back
panel adjustments. Instead, we discuss the basic acoustical concepts needed to get the
most out of your SDA-102 and present examples of several practical applications.
Special thanks to
Hans Drobilitsch of
Hans Drobilitsch
Audio GmbH.
(Wollersdorf,
Austria) for his
invaluable technical
advice.
Loudspeaker Synchronization
Sound travels at about 1,130 feet per second in air, or about 1 millisecond per foot. On the
other hand, electronic signals travel almost one million times faster through your sound
system to the loudspeakers. The main task of digital delays is to synchronize multiple
loudspeakers so the sound traveling different distances arrives at the listener’s ears at about
the same time. Synchronizing the loudspeakers reduces reverberation and echoes for
improved intelligibility.
How to Synchronize Your Signals
There are several powerful tools available for precisely measuring the time a loudspeaker
signal takes to arrive at a certain point in the audience. Most of these tools are very sophisticated and tend to be quite expensive. Fortunately, simpler tools are sufficient for most
applications.
In the 1930’s, engineers synchronized the low and high frequency speakers in movie theaters
by feeding a sharp click through the system. They moved the speakers until they could only
hear a single sharp click coming from both speakers. You can use this same method with a
common child’s toy called a clicker. Pressing the thin metal strip makes a loud sharp click.
A clicker is especially useful when synchronizing the direct sound from the performer with the
sound from the loudspeakers.
Alternatively, you can use a phase checker especially for synchronizing the signals of two
loudspeakers (either LF and HF or two full range systems) since most of the phase checkers
include a click generator and receiver. Phase checkers are quite affordable and have other
uses besides synchronizing.
Processing (or Group) Delays
Converting signals back and forth from the analog to digital domain always delays the signal
a little. These conversion delays are often called processing (or group) delays, and usually
range between 0.9 to 5 milliseconds. You will notice that Sabine delays always display the
processing delay as the smallest possible delay value. For the SDA-102, the processing
delay is 0.9 milliseconds. You can simply bypass the unit for 0 seconds delay.
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Not all manufacturers acknowledge processing delays in their specifications, but you must
take them into account when synchronizing your system. Make sure all digital equipment is
on and not bypassed when synchronizing. Also, be careful to make an appropriate adjustment in your delay lines if you later add any type of digital equipment to the system.
Center Cluster Speakers
Center cluster speakers offer several advantages over systems that have speakers mounted
on the sides. The most obvious advantage is that the distance to the closest and most
distant locations in the audience is almost equal, so most listeners hear about the same
level. Center clusters also offer two other advantages regarding the visual imaging.
Studies have shown that people can detect even small horizontal changes in the direction of
a sound source, but vertical shifts are much less noticeable. This suggests that the sound
from center-cluster speakers is more likely to be visually aligned with the performer than
loudspeakers placed on each side of the stage.
All those in the audience who are closer to the performer than the center cluster will hear the
direct sound from the performer before they hear the sound from the loudspeakers. This
makes the sound seem to come from the performer, not the loudspeakers. (See the Precedence Effect below.)
Comb Filter Distortion
Many who took high school science may remember ripple tank experiments where waves are
generated from two separate point sources. The waves from each source combine to form
visible interference patterns. In some places, the wave crests and troughs are in phase so
they combined to make a larger wave. In other places the crests are out of phase, so the
crest of one wave source is canceled by the trough of the other. Ripple tank experiments
show the interference patterns are strongest when the amplitude of the waves from each
source is equal.
A similar interference occurs in sound systems when a signal is delayed and mixed back into
the original signal. These interference patterns are called COMB FILTERS because their
frequency response plots look like the teeth of a comb (see Figs. 1 & 2). There are a number
of common situations that cause comb filters. For example, when the program is played
through two loudspeakers, the loudspeaker that is farther away interferes with the closer
loudspeaker. Comb filters are also created when a performer is picked up by two microphones, one closer than the other. You even introduce comb filters by mixing digital effects
back into the “dry” signal at the mixer’s effects loop.
Fig. 1:
COMB FILTERS. Input
signal mixed with a 2 msec.
delayed signal. (Both signals
have the same amplitude.
Max. filter gain is +6dB, and
max. depth is -4.)
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