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Admin: Created page with "Click here to open the tutorial patch: 04fSubtractiveSynthesis.maxpat In this tutorial, we'll look at using filters creatively with a group of MSP audio generators that..."

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Created page with "Click here to open the tutorial patch: 04fSubtractiveSynthesis.maxpat In this tutorial, we'll look at using filters creatively with a group of MSP audio generators that..."

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Click here to open the tutorial patch: [[04fSubtractiveSynthesis.maxpat]]

In this tutorial, we'll look at using filters creatively with a group of
MSP audio generators that create different kinds of {{maxword|name=noise~}}.
Noise generation is a core component of ''subtractive synthesis'',
a sound design methodology that works by taking complex signsl and
sculpting them with filters, subtracting energy from the original
signal (compare this with additive synthesis, which works in the
opposite fashion). Along the way, we'll discuss ways to shape this
noise using an object that creates and controls a ''bank'' of
parallel filters.

===Noise===

Take a look at our tutorial patcher. It consists of three patcher regions.
If we look at the area labeled <code>1</code>, we can see that we have three new
MSP objects connected through {{maxword|name=*~}} objects to the {{maxword|name=dac~}}.

* Turn on the audio in the patcher by clicking on the {{maxword|name=ezdac~}} object. Adjust the {{maxword|name=number}} box
that controls the volume for the {{maxword|name=noise~}} object and listen to
the result. Turn it down and turn up the volume for the {{maxword|name=pink~}} object.
Do the same for the {{maxword|name=rand~}} object. Click in the {{maxword|name=number}} box
that is connected to the inlet of the {{maxword|name=rand~}} object (labeled 'Frequency').
Type <code>100</code> and hit return. Try <code>1000</code> and hit return.Experiment with
other values.

The {{maxword|name=noise~}}, {{maxword|name=pink~}}, and {{maxword|name=rand~}} objects all generate ''noise''
at a signal rate. Noise, at its essence, is a type of random number generation;
as a result, these objects behave in a similar manner to Max objects
such as {{maxword|name=random}} and {{maxword|name=drunk}}.

The {{maxword|name=noise~}} object generates ''white noise'', which means that all
possible frequencies in the audio spectrum are equally represented over time.
The process of generating white noise digitally is quite simple: every sample,
pick a random number between <code>-1</code> and <code>1</code>:

[[Image:Filterchapter04a.png|border]]
''A waveform and spectrogram plot of white noise.''

The {{maxword|name=pink~}} object generates ''pink noise'', which means that
every ''octave'' in the audio spectrum has equal weight. This is
sometimes referred to as ''1/f'' noise, as the probability of a
frequency occuring is the inverse of its value, e.g. frequencies of
100 Hz are twice as probable as 200 Hz. The aural difference between
the two is fairly obvious: white noise has far more high frequency
content and sounds 'harsher' than pink noise:

[[Image:Filterchapter04b.png|border]]
''Pink (1/f) noise: waveform and spectrogram.''

The {{maxword|name=rand~}} object is a random number generator that generates a
signal, picking a new random value for that signal at a variable rate.
It takes an argument (or a value at its inlet) to set the frequency of
the random number selection. A frequency of <code>44100</code> makes the object
indistinguishable from white noise. This allows us to create ''band-limited'' noise
that has an upper boundary we can specify:

[[Image:Filterchapter04c.png|border]]
''A {{maxword|name=rand~}} object picking values at <code>1000</code> Hz: waveform and spectrogram.''

===Filtering noise===

Because noise has such broadband frequency content, it can be filtered
and sculpted to create very precise timbres. The compositional technique
of subtractive synthesis relies on this attribute of noise generation; it's
often easier (or more efficient) to start with noise and filter it down then
attempt to create the desired timbre through adding oscillators.

* Turn down the volumes in patcher area <code>1</code> and take a look at patcher
area <code>2</code>. Turn up the volume using the {{maxword|name=number}} box at the bottom
of the signal chain (controlling the {{maxword|name=*~}} object connected to the {{maxword|name=dac~}}).
Click in the {{maxword|name=number}} box labeled 'Frequency' connected to
the {{maxword|name=phasor~}} object, type <code>0.1</code> and hit return. Type a higher
frequency (e.g. <code>3.0</code>) and hit return. Experiment with different values.

Patcher area <code>2</code> contains a {{maxword|name=noise~}} object sending its signal into
a {{maxword|name=lores~}} filter. The frequency of the lowpass filter is being modulated
by a {{maxword|name=phasor~}}, which we've scaled to ramp between <code>100</code> and <code>600</code>
at the frequency we specify. As a result, the cutoff frequency of the filter 'sweeps'
at regular intervals. This is an example of an ''LFO'', or ''low-frequency oscillator'',
being used to modulate a parameter of an audio processing system. As you can hear,
the {{maxword|name=lores~}} object attenuates the high frequencies output from the {{maxword|name=noise~}} object.
In addition, the resonance value of the {{maxword|name=lores~}} causes the filter to
have a peak just below its cutoff frequency, giving a notably 'pitched' sound
to the filtered noise.

===Banks of filters===

* Turn down the volume on area <code>2</code> in the tutorial patcher and take
a look at area <code>3</code>. One-by-one, turn up and down the {{maxword|name=gain~}} sliders
connected to the {{maxword|name=dac~}} object.

The {{maxword|name=fffb~}} object stands for ''Fast, Fixed, Filter Bank''. Unlike
the {{maxword|name=cascade~}} object, which implements a number of {{maxword|name=biquad~}} filters
in series, the {{maxword|name=fffb~}} object arranges a number of {{maxword|name=reson~}} objects
in ''parallel'', which is to say that the settings of one filter will not
affect any of the others. The {{maxword|name=fffb~}} object takes a number of arguments
which set its behavior: the ''number'' of filters, the ''base frequency'' of
the filter bank, the ''ratio'' between filters, and the ''Q'' of the filters.
All of the parameters of the object with the exception of the number of filters
can be changed with Max messages; the number is fixed because, as we can see,
each filter connects to a separate outlet. This allows us to create filter banks,
where we can 'tap' each bandpass filter individually:

[[Image:Filterchapter04d.gif"/><img src="images/filterchapter04e.png|border]]
''Output of the lowest and highest two filters in our {{maxword|name=fffb~}} object:
waveform and spectrogram.''

* Using the mouse, click and drag on the {{maxword|name=dial}} object in patcher area <code>3</code>.
This has the audible effect of shifting the entire filter bank upwards or
downwards. Turn up different {{maxword|name=gain~}} sliders to hear the results.

The value from the {{maxword|name=dial}} is interpreted as a MIDI pitch, converted
to frequency (via the {{maxword|name=mtof}}) object, and used to format the <code>freqRatio</code>
message to the {{maxword|name=fffb~}} object. The <code>freqRatio</code> message takes
two arguments: the center frequency of the first (lowest) filter,
and the ''ratio'' between it and subsequent filters. The
letter <code>H</code>, when used as the ratio, tells the {{maxword|name=fffb~}} object
to set the filters in the bank to ''harmonic'' multiples of the base
frequency. So the message <code>freqRatio 100. H</code> would set our ten
filters up to be centered to <code>100</code> Hz increments.

* Click in the <link type="refpage" name="number">number box</link> objects connected to the {{maxword|name=pak}} object.
Type <code>200.</code> in the lefthand {{maxword|name=number}} box, and <code>1.5</code> in
the righthand {{maxword|name=number}} box. Click on the {{maxword|name=number}} box connect
to the <code>message</code> box containing the message <code>QAll $1</code>. Enter
the value <code>100.</code> and hit return. Turn up and down the
different {{maxword|name=gain~}} sliders to hear the results.

We can easily set our filters in a frequency ratio other than a
harmonic series. Setting our base frequency to <code>200.</code> and
our ratio to <code>1.5</code> results in a bank of ten filters set to
the frequencies <code>200, 300, 450, 675, 1012.5, 1518.75, 2278.125,
3417.1875, 5125.78125, 7688.671875, and 11533.0078125</code> Hz,
respectively. As with the {{maxword|name=reson~}} object, we have direct
control over the ''Q'' of these filters. A Q of <code>100</code> r
esults in a bandwidth of 1/100 the frequency, creating narrow,
pitched filters.

* Click the <code>message</code> box to the right of patcher area <code>3</code>
that contains a series of lists. Listen to the results by adjusting
the {{maxword|name=gain~}} sliders.

The {{maxword|name=fffb~}} object takes many other messages, enabling
us to set the filters not in ratio at all. Sending lists in
the format <code>filter_# frequency Q</code> allows us to set each
filter in the bank individually. In our example, we've set the
ten filters to frequencies from a musical chord.

===Metering===

Next to each {{maxword|name=gain~}} slider in patcher area <code>3</code> is a
user-interface object that registers the amplitude of the signal
connected to it. These {{maxword|name=meter~}} objects allow us to see the
gain of each filter in the {{maxword|name=fffb~}} ''pre-fader'',
i.e. before we listen to it.

* Turn down all the {{maxword|name=gain~}} sliders in patcher area <code>3</code>. Click
in the {{maxword|name=number}} box that triggers the <code>Qall</code> message.
Type <code>0.5</code> and hit return. Type <code>10.</code> and hit return. Listen
to the results and notice the effect of the Q on the gain of each filter,
and look at how the {{maxword|name=meter~}} objects respond.

Because the {{maxword|name=fffb~}} object works in parallel, the output gain of
all the filters in the bank will typically be ''greater'' than the
gain of the incoming signal. Depending on the Q values and the frequencies
used, the potential volume output from the {{maxword|name=fffb~}} can be quite
high. The {{maxword|name=meter~}} object lets you observe your volumes visually
in the patcher window ''before'' you listen (and potentially hurt
your ears).

===Summary===

MSP has three simple-to-use noise generator objects, which generate white
noise ({{maxword|name=noise~}}), pink noise ({{maxword|name=pink~}}), and band-limited random
signals ({{maxword|name=rand~}}). These objects are ideal candidates for filtering.
The {{maxword|name=fffb~}} object implements a fixed filter bank of parallel bandpass
filters which can be controlled via ratios of a base frequency or individually.
The {{maxword|name=meter~}} object allows you to visually see the amplitude of any part
of the MSP signal path, and is incredibly useful for metering and debugging
your audio patchers.

===See Also===

{{maxword|name=noise~}} - White noise generator

{{maxword|name=pink~}} - Pink noise generator

{{maxword|name=rand~}} - Band-limited random signal

{{maxword|name=fffb~}} - Fast fixed filter bank

{{maxword|name=meter~}} - Visual peak level indicator

[[Category:Teaching Material]]

← Older revision		Revision as of 15:31, 28 June 2012
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−	Click here to open the tutorial patch: [[04fSubtractiveSynthesis.maxpat]]	+	Click here to open the tutorial patch: [[Media:04fSubtractiveSynthesis.maxpat]]

	In this tutorial, we'll look at using filters creatively with a group of MSP audio generators that create different kinds of {{maxword\|name=noise~}}. Noise generation is a core component of ''subtractive synthesis'', a sound design methodology that works by taking complex signsl and sculpting them with filters, subtracting energy from the original signal (compare this with additive synthesis, which works in the opposite fashion). Along the way, we'll discuss ways to shape this noise using an object that creates and controls a ''bank'' of parallel filters.		In this tutorial, we'll look at using filters creatively with a group of MSP audio generators that create different kinds of {{maxword\|name=noise~}}. Noise generation is a core component of ''subtractive synthesis'', a sound design methodology that works by taking complex signsl and sculpting them with filters, subtracting energy from the original signal (compare this with additive synthesis, which works in the opposite fashion). Along the way, we'll discuss ways to shape this noise using an object that creates and controls a ''bank'' of parallel filters.

@@ Line 103: / Line 103: @@
 where we can 'tap' each bandpass filter individually:
-[[Image:Filterchapter04d.gif"/><img src="images/filterchapter04e.png|border]]
+[[Image:Filterchapter04d.gif|border]]
 ''Output of the lowest and highest two filters in our {{maxword|name=fffb~}} object:

MSP Filter Tutorial 4: Subtractive Synthesis - Revision history

Gtaylor@rtqe.net at 15:31, 28 June 2012

Admin at 21:19, 25 June 2012

Admin at 21:25, 22 June 2012

Admin at 21:23, 22 June 2012

Admin: Created page with "Click here to open the tutorial patch: 04fSubtractiveSynthesis.maxpat In this tutorial, we'll look at using filters creatively with a group of MSP audio generators that..."