Sonnox Oxford Restore User Manual

Operation Manual

1

Sonnox

Sonnox Restore Operation Manual

SonnoxSonnox

1. Introduction

The Sonnox Restore suite is a collection of three plug-ins designed to clean the sound of digital
audio recordings that are damaged:

• by pops, clicks, or crackle;

• by hum, buzzes and whines;

• or by noise.

The tools are not just for restoring old material, but also for removing the clicks, pops, buzzes
and background noises that can sometimes accidentally occur in new recordings.

A great deal of time has been put into making the Sonnox Restore suite as intuitive as possible in
terms of providing excellent visual and graphical feedback. They also include some innovative
solutions not seen before in the restoration field, the intention being to enable quick and accurate
repair of a variety of spoiled recordings.

Restoration Processing Workflow

It is usual practice to use the DeClick process first, particularly if there are large disturbances
present that require repair.

The optimal order for DeNoise and DeBuzz is probably dependent on the programme material. If
a loud buzz is dominating low-level noise it would be sensible to remove the buzz first; on the
other hand the presence of significant noise might make it more difficult for the DeBuzz detector
to lock on to a low level buzz component.

2. Supported Platforms

Digidesign ProTools (LE, RTAS, M-Powered)
VST
Audio Units

Mac OSX 10.4 or later (PowerPC and Intel)
Windows XP

See supplement for platform specific details.

2

3. The Oxford DeClicker

3.1 Basic Operation

The Oxford DeClicker has three main sections: DePop, DeClick and DeCrackle. These three
sections deal with events that are up to 10ms, 3ms and 0.4ms in duration, respectively.

Each of the three sections calculates an Excitation Profile for a given block of samples. The
excitation profile is the residual signal left after harmonic components have been removed, and is
a representation of how much the actual signal is deviating from the predicted signal. A big
excitation usually represents a big unexpected event such as a click.

Each section provides a Threshold control. This control is used to adjust a threshold level within
the excitation profile to capture an event. If a peak on the excitation profile is below the
threshold, it will not be registered as an event to be repaired. If a peak breaches the threshold
line, then it is registered as a detected event and can be repaired. When you touch the Threshold
control, by default the excitation profile is displayed visually on the graph. Usually there is a
background level of “noise” at the bottom with the occasional peak lifting above the background.

3

You can imagine a click as a triangular shaped peak in the excitation profile, wider at the bottom
and tapering to a point at the top. Keeping this in mind, you have two potential strategies for
detecting and repairing a click.

The first is to lower the threshold in the
excitation profile until it is just above the
noise floor, near the base of the triangle.
(You can do this either with the Threshold
slider, or drag the threshold line on the
graph itself.) This means that the true
width of the event is more likely to be
found because the threshold is further
down the triangle at the base.

The problem with this approach is that
now many events are registered for
potential repair. As the Sensitivity setting
is reduced, more and more detected events

are rejected and discarded, starting with
the smallest. Thus a low sensitivity means only the largest of the detected events go forwards to
the repair section.

The “Threshold” control determines how many events are detected, and the
“Sensitivity” control determines how many of those detected events go on to be
repaired.

The best setting for the Threshold slider is to put it where the threshold line on the excitation
profile is just above the noise floor, and to lower the Sensitivity slider until the required number
of repairs are occurring.

The other approach is to lower the Threshold until it is just under the top of the peaks. With
Sensitivity at maximum, you are then only correcting the events that breach the threshold. One
potential problem with this method is that it is possible that only the middle of the event is
actually repaired because the width of the event is perceived to be narrower than it actually is
(because the Threshold is at the peak of the triangle where it is narrowest.) In practice, however,
any partial repairs can be fully repaired later on by the DeCrackle section which does tend to
clean up the repairs done in the DePop and DeClick sections.

4

The DePop section can detect events from 10ms down to 1ms. However, it is best to adjust the
DePop Threshold and Sensitivity to ensure that the fewest repairs are done in this section. Use a
low DePop Threshold and a minimum of Sensitivity to achieve this.

If possible, use the DeClicker section to capture the longest and widest of the clicks. Again use a
low DeClick Threshold and a minimum of Sensitivity to achieve this.

3.2 Output Panel

The listen section of the Output Panel contains an option to listen to the difference between the
input and the processed output. This is labeled “Diff”. This is particularly useful in this plug-in
for hearing what has been repaired, and for listening to the quality of the repairs without being
distracted by the audio material. You can also listen for breakthrough of audio on the pops,
meaning that the repair is too wide (you need to raise the DePop Threshold a bit). You can listen
for a constant scratching sound, which means that the DeCrackle section may be doing too many
repairs, particularly if you can’t hear that scratching sound in the original. You can listen to make
sure that the sound of the clicks is as close as possible to the sound of the clicks in the original. If
they are brighter, it may mean that the DeClick Threshold slider needs to go lower to capture the
true width of the clicks.

3.3 The Events Graph

The events graph is an important visual display, showing events as they are being detected. The
events are shown with duration along the X-axis and amplitude/energy along the Y-axis. It is
worthwhile playing with the Threshold and Sensitivity controls to see their effect on the number
of events that are detected, and at what level and width they are displayed on the event graph.

For example, you will notice that as you bring the Threshold lower, not only are more events
detected, but the events tend to move to the left, meaning the events are being detected as longer
duration. Then as you move the Sensitivity down, you will notice that the smallest events
disappear first, leaving the largest events.

The graph shows green bubbles (DePop), blue bubbles (DeClick) and white bubbles
(DeCrackle). The size of the bubbles indicates how loud they are, as does their height above the
horizontal axis. Each section has an IN button, and if you disable a section using the IN button,
their bubbles are displayed as Red, meaning these events have been detected but not repaired.

5

Clicking in the Events Graph will remove any popup graphs such as the Excitation Profiles to
expand your view of the Events.

3.4 The Exclude Box

The Events Graph allows an important new feature to be implemented. The idea of the exclude
box is to stop over-corrections. For example, you may be happy with a piece of music and the
associated repairs, except for a section with brass instruments - at which point too many high
energy events are detected and corrected. Likewise, with dialogue you sometimes find that the
need for repairs diminishes as the dialogue becomes louder, because the dialogue masks the
clicks. Threshold and Sensitivity settings that work for the background noise of the dialogue
may be too sensitive when the dialogue is active and loud. The graphic representation of the
detected events makes this visually very obvious, and can be further demonstrated by listening to
the diff signal.

One way to remedy these situations is to
use an Exclude Box. Simply click the
pointer in the event graph area to create a
box and drag it to where it needs to be to
exclude the repairs that were undesirable.
Every event that occurs inside the box
will not be repaired and is displayed in
red. You can drag the whole box or use
the drag handles (left, right, top, bottom)
to re-position or re-size the box
accurately.

The diagram shows the tell-tale signature
of a loud brass section of music. If these
events were to be “repaired” by the
declicker, the section would lose all brightness and authenticity. Using the exclude box the
events can be marked for exclusion from the repair processing.

There are two further controls for the Exclude Box; one to enable or disable the feature (Exclude
Box Enable), and one to show or hide the box (Exclude Box Show). Both of these controls
leave the box position unchanged. These controls are automatable, as are the drag handles. Only
one exclude box can be active at a time.

6

3.5 Dialogue Mode

The Dialogue Mode is another unique feature of the Oxford DeClicker. It is a complete solution
to the problems associated with dialogue where you need one set of Threshold/Sensitivity
settings for the background level, when the speaker is pausing, and a quite different set of
Threshold/Sensitivity settings whilst speaking.

When you enable Dialogue Mode the background GUI changes to display an extra panel. You
now have two entire sets of Threshold/Sensitivity/Enable controls at your disposable. One set
is for the quieter parts, and one set for the louder parts. Access to these two sets of controls is via
the Above Set and Below Set buttons. The Voice Threshold control is a threshold level that
determines which set of controls processes a given signal. If the signal level is above the
threshold, then it is processed by the controls labeled Above. If the signal is below the threshold,
it is processed by the controls labeled Below.

On switching to Dialogue Mode, the first thing to do is set the Voice Threshold slider. When
you touch this slider you see the history of the signal level. You can easily set the threshold using
the fader to be just above the background level while the speaker pauses. You can also drag the
threshold line on the graph.

Set the Threshold/Sensitivity controls
of the Below controls, or drag the
threshold lines on the graphs to
appropriate background settings.

Then click the Above Set button, to
switch the controls over to displaying
the “Above Set” of controls. Set these
Threshold/Sensitivity controls or drag
the threshold lines on the graphs to
appropriate settings for the speech.

The final feature of the Dialogue Mode
that makes it even more flexible is the
incorporation of a Side-Chain. This

feature further defines when the signal level is “Above” the Voice Threshold and when it is
“Below”. Without the side-chain, the Above / Below splitting occurs purely on the
level/amplitude of the signal. When you use the side-chain, Above / Below splitting occurs on
the level of the signal within a particular frequency band.

7

3.6 Description of Controls

Touch Pad Controls

Several controls in these plug-ins use a Touch Pad associated with a knob or slider. These
controls give a clear display of the SI value of a control, and respond to the following actions:

- Left-Click and drag up/down: Increase/decrease the value

- Right-Click and drag up/down: Fine adjustment of value

- Double Click: Directly edit value

- Shift + Left-Click and drag up/down: Fine adjustment of value

- Control + Left-Click: Set to default

Input and Output Sections

“Meters” – The input and output meters indicate 1dB per segment for the top 18dB of dynamics
range, and 2dB per segment thereafter.

“Trim” – The input trim has a range of +12dB to -12dB. The output trim has a range of 0.0dB to

-12dB

“Listen Audio” – Selects auditioning of the cleaned audio signal.

“Listen Diff” – Selects auditioning of what is being removed from the audio signal.

“Listen Side Chain” – Selects auditioning of the side chain.

“Dialogue Mode” – Selects the Dialogue Mode and displays the Dialogue control panel.

“Master Enable” – With Master Enable selected, all processing is active. If not selected, all
repairs are disabled, although all the detection circuits remain active.

The Master Enable, Audio and Diff buttons all provide smoothly interpolated and glitchless
audio switching. It is advisable to use these for auditioning, rather than using the host
application’s Bypass switch (which is commonly not interpolated).

DePop, DeClick and DeCrackle Sections

“Threshold” – This control is used to adjust a threshold level within the Excitation Profile to
capture an event. If a peak on the Excitation Profile is below the threshold, it will not be

8

registered as an event to be repaired. If a peak breaches the threshold line, then it is registered as
a detected event and can be repaired.

“Sensitivity” – This control determines whether detected events are discarded, starting with the
smallest. A low Sensitivity means only the largest of the detected events go forwards to the
repair section.

“Enable” –With the section disabled, the detectors are still monitoring the audio and any
detected events are shown on the Events Graph as red bubbles. Setting the section IN will
present the detected events to the repair processing section.

“Detect Meter” – The Detect meter display combines two indications. The main rising column
indicates the sum of the energy of events that have been detected. With the “Enable” button de­selected (ie. the repair circuit disabled), this column is coloured orange/red. With the repair
circuit active the column is coloured blue. The bottom segment of the meter is an indication of
each individual detected event.

Dialogue Mode

“Voice Threshold” – This control determines the threshold at which detected events are
allocated between the two sets of Detect/Repair settings. Any event detected while the level is
above the threshold (coloured blue) will be allocated to the Above Set; any event detected while
the level is below the threshold (coloured red) will be allocated to the Below Set.

“Above Set” – With Above Set selected, the Detect/Repair controls are used on events that are
above the Voice Threshold.

“Below Set” – With Below Set selected, the Detect/Repair controls are used on events that are
below the Voice Threshold.

“Side-Chain LF Filter” – Sets the LF limit for the side-chain.

“Side-Chain HF Filter” – Sets the HF limit for the side-chain.

Display Controls

“Exclude Box Enable” – This control enables or disables the Exclude Box. This the box
enabled, any event inside the box will not be repaired.

9

“Exclude Box Show” – This control shows or hides the Exclude Box. The status of Exclude
Box Enable is not affected.

“Pop-ups” – This control enables or disables the following display modes:

- Disable Pop-ups

- Pop-ups follow touch (Default)

- Show Excitation Profile

- Show Level Profile (for Dialogue Mode)

- Show Spectrum (for Dialogue Mode)

“Display Options” – This control enables or disables many display options:

- Events decay, or persist indefinitely;

- X-axis graduated in log or lin, and samples or milliseconds;

- Y-axis graduated in peak amplitude or RMS energy

- Labelling of detected events

Sonnox Menu Button

“Clip Lights” – Can be set to hold for 2 seconds, 5 seconds, or indefinitely.

“Show Preset Name Path” – Can show or hide the preset name path in the Preset Manager.

“Knob Mode” – Can be set to circular, relative circular, linear or follow host.

“About” – Displays the date, version and build number of the plug-in.

10

3.7 DeClicker Signal / Control Flow Diagram

3.8 DeClicker Stereo Behaviour

For correct stereo operation, when instantiated into a stereo track the DeClicker has two
independent detect and repair circuits.

11

4. The Oxford DeBuzzer

4.1 Basic Operation

The Oxford DeBuzzer is divided into two stages: Detection and Removal.

Removal of buzz is usually accomplished by using a comb filter. The comb filter has many tight
notches in the frequency spectrum that eliminate the fundamental frequency and associated
harmonics of a buzz.

For this process to work well, the frequency of the fundamental must be very accurately
determined. There are several tools available to help isolate the fundamental frequency. The first
is the Peak Profile that is displayed immediately above the big central rotary control. This is a
plot of strength of a given nominal frequency in the input signal, and the display extends over a
wide range either side of the nominal frequency. With the nominal set to 50Hz, any peak
frequency between 45Hz and 55Hz will be displayed.

12