Gtaylor@rtqe.net at 15:30, 28 June 2012

2012-06-28T15:30:06Z

Admin at 21:12, 25 June 2012

2012-06-25T21:12:23Z

Admin at 21:11, 25 June 2012

2012-06-25T21:11:51Z

Admin: Created page with "Click here to open the tutorial patch: 02nDynamicsProcessing.maxpat This tutorial looks at using envelope following techniques to create ''dynamics processors'' in MSP...."

2012-06-22T21:11:23Z

Created page with "Click here to open the tutorial patch: 02nDynamicsProcessing.maxpat This tutorial looks at using envelope following techniques to create ''dynamics processors'' in MSP...."

New page

Click here to open the tutorial patch: [[02nDynamicsProcessing.maxpat]]

This tutorial looks at using envelope following techniques to create
''dynamics processors'' in MSP. Once we've derived the amplitude envelope
of a waveform as a control signal, we can add patcher logic to make decisions
on the overall gain of a signal. This allows us to make compressors, limiters,
and gates based on the time-varying amplitude of our audio.

* In the tutorial patcher, look at the area labeled <code>1</code>. This is a simple
playback patcher that takes a {{maxword|name=buffer~}} and loops it using
a {{maxword|name=groove~}} object. Turn on the audio by clicking the {{maxword|name=ezdac~}} and
turn up the {{maxword|name=gain~}} slider to hear the sound. Note that the audio from
the {{maxword|name=groove~}} object goes into a {{maxword|name=send~}} object named <code>audio</code>.
We'll pick up this audio in the subpatchers within the tutorial patcher. Turn
down the {{maxword|name=gain~}} slider and doubleclick the {{maxword|name=patcher}} object
labeled 'Compressor/Limiter'.

===Audio compression and limiting===

If we have an audio signal containing a wide range of amplitudes (such
as a drum loop or expressive vocals) it's often necessary to reduce,
or ''compress'', this range. A ''compressor'' algorithm reduces
the dynamic range of an audio signal by tracking its envelope and checking
that value against a ''threshold'' number. When the audio signal exceeds
the threshold, its gain is reduced by a scaling factor called a
compression ''ratio''. We can change the behavior of a compressor by
adjusting its ''threshold'' and ''ratio'', as well as by making intelligent
decisions regarding the way in which the envelope signal is derived.

* In the tutorial {{maxword|name=patcher}} labeled 'Compressor/Limiter', turn up
the {{maxword|name=gain~}} slider. Note the difference between the sound and the sound
of the uncompressed drum loop in the main patcher. Click in the {{maxword|name=number}} box
labeled 'Threshold' and lower its value to <code>0.2</code>. Raise the {{maxword|name=number}} box
labeled 'Ratio' to <code>30.</code>. Listen to the results. Change the 'Decay' value
to <code>200</code>. Bring the ratio back down to <code>4.</code>, and the threshold to <code>0.5</code>.
Try raising the 'Attack' value. Listen to the results as you play with the controls,
and look at the {{maxword|name=multislider}} objects at the bottom of the patcher.

Our compression patcher contains the standard controls that we would find
on a hardware compressor box or a dynamics plug-in for a DAW program.
The 'Attack' and 'Decay' controls set parameters for the envelope following
of the audio signal. These values (converted from milliseconds to samples by
the {{maxword|name=*}} objects) set how fast the {{maxword|name=rampsmooth~}} object allows the
envelope to rise and fall based on the incoming signal. A long attack and
decay will make the compressor circuit less responsive, but will also limit
some of the artifacts associated with a highly responsive compressor, such as
audible 'pumping' of the gain. The 'Threshold' and 'Ratio' controls alter how
the compressor deals with scaling the gain. Our circuit implements the following
equation to set the gain, where <code>g</code> is the gain, <code>e</code> is the envelope
signal, and <code>t</code> and <code>r</code> are the threshold and ratio, respectively:

g = ( (e-t)*(1/r) + t ) / e; 0<=g<=1.

This gain value <code>g</code> is clipped in the range of <code>0.</code> to <code>1.</code> and
then multiplied by our original audio to control its volume. The envelope
value <code>e</code> and output gain <code>g</code> are shown in the patcher in
the {{maxword|name=multislider}} objects labeled 'Enveloped' and 'Reduction'. The
colors in the 'Reduction' {{maxword|name=multislider}} are flipped so that the colored
area is greater as the gain is lower, visually cueing us into the fact that the
audio volume is being ''attenuated'' by our compressor.

* Set the 'Attack', 'Decay', and 'Threshold' to <code>10.</code>, <code>100.</code>, and <code>0.5</code>,
respectively. Click on the <code>message</code> box containing the value <code>0.</code> and
labeled 'Limiter?'. Listen to the results.

A ''limiter'' is a compression circuit with an infinite compression ration,
i.e. sound above the threshold is attenuated to never exceed that threshold.
For a limiter, the <code>r</code> term is infinite, zeroing out part of the equation:

g = t / e; 0<=g<=1.

* Experiment more with different compression settings to see how the
circuit responds. Note that the circuit always attenuates the signal,
so at very low thresholds it may be necessary to raise the {{maxword|name=gain~}} slider
to hear the results. When you've finished, turn down the {{maxword|name=gain~}} slider,
return to the main tutorial patcher, and open the {{maxword|name=patcher}} named 'Gate'.

===Audio gating===

* Look at the contents of the subpatcher named 'Gate': the settings
are similar to the compression example, but the results are quite
different. Turn up the {{maxword|name=gain~}} slider and listen to the results
of the circuit. Look at the {{maxword|name=multislider}} objects and see how
they respond to the drum loop.

The MSP circuit in this patcher starts on the same premise of a
compressor: that of an envelope follower and a threshold. Rather
than reducing the gain of audio energy that exceeds the threshold,
however, this circuit attenuates signals that fall ''below'' it.
This type of dynamics compression is called a ''gate'' (it is also
sometimes referred to as a ''noise gate''). Unlike a compressor,
however, the gate has a ''knee'' setting instead of a compression
ratio. This setting is a proportion of the threshold within which the
audio is attenuated rather than cut altogether. So with the default
settings in the tutorial patch, we can expect the following results:

Sound above <code>0.5</code> are left alone (<code>g</code> = 1).

Sound below <code>0.5</code> and above <code>0.375</code> (the threshold * the knee) are scaled between 0 and 1.

Sound below <code>0.375</code> are gated out (<code>g</code> = 0)

In equation form, our gate looks something like this, where <code>g</code>
is the gain, <code>e</code> is the envelope signal, and <code>t</code> and <code>k</code>
are the threshold and knee:

g = (e-(t*k)) / (t-(t*k); 0<=g<=1.

As with our compressor, <code>g</code> is clipped between <code>0</code> and <code>1</code>.

* Familiarize yourself with the gate settings. Set the knee as high as
it will go, and notice at the gate effect now simply cuts in and out.
Set the knee to a low value, and the gate will fade in and out smoothly.
See how the 'Attack' and 'Decay' controls on the envelope follower effect
the ability of our gate to track the beat of the drum loop and gate out the
silences.

===Summary===

Dynamics processors in MSP can be constructed using signal
processing algorithms that take an envelope follower output
as their control signal. Compressors and limiters attenuate
audio signals that exceed a certain amplitude threshold according
to their envelopes; gates attenuate audio that falls below a threshold.
The parameters of the envelope follower itself control the responsiveness
of the dynamics circuit, while parameters such as the threshold
and ratio / kne. control the 'sound' of the processing.

[[Category:Teaching Material]]

← Older revision		Revision as of 15:30, 28 June 2012
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−	Click here to open the tutorial patch: [[02nDynamicsProcessing.maxpat]]	+	Click here to open the tutorial patch: [[Media:02nDynamicsProcessing.maxpat]]

	This tutorial looks at using envelope following techniques to create ''dynamics processors'' in MSP. Once we've derived the amplitude envelope of a waveform as a control signal, we can add patcher logic to make decisions on the overall gain of a signal. This allows us to make compressors, limiters, and gates based on the time-varying amplitude of our audio.		This tutorial looks at using envelope following techniques to create ''dynamics processors'' in MSP. Once we've derived the amplitude envelope of a waveform as a control signal, we can add patcher logic to make decisions on the overall gain of a signal. This allows us to make compressors, limiters, and gates based on the time-varying amplitude of our audio.

@@ Line 45: / Line 45: @@
 * Familiarize yourself with the gate settings. Set the knee as high as it will go, and notice at the gate effect now simply cuts in and out. Set the knee to a low value, and the gate will fade in and out smoothly. See how the 'Attack' and 'Decay' controls on the envelope follower effect the ability of our gate to track the beat of the drum loop and gate out the silences.
- ===Summary===
+===Summary===
 Dynamics processors in MSP can be constructed using signal processing algorithms that take an envelope follower output as their control signal. Compressors and limiters attenuate audio signals that exceed a certain amplitude threshold according to their envelopes; gates attenuate audio that falls below a threshold. The parameters of the envelope follower itself control the responsiveness of the dynamics circuit, while parameters such as the threshold and ratio / kne. control the 'sound' of the processing.
 [[Category:Teaching Material]]

MSP Dynamics Tutorial 2: Envelope Following - Revision history

Gtaylor@rtqe.net at 15:30, 28 June 2012

Admin at 21:12, 25 June 2012

Admin at 21:11, 25 June 2012

Admin: Created page with "Click here to open the tutorial patch: 02nDynamicsProcessing.maxpat This tutorial looks at using envelope following techniques to create ''dynamics processors'' in MSP...."