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Thursday, 23 May 2013

My Talk at the Sc Symposium

Picking Musical Tones

One of the great problems in electronic music is picking pitches and tunings. The TuningLib quark helps manage this process.

First, there is some Scale stuff already in SuperColider.

How to use a scale in a Pbind:

(
s.waitForBoot({
     a = Scale.ionian;

     p = Pbind(
          \degree, Pseq([0, 1, 2, 3, 4, 5, 6, 7, 6, 5, 4, 3, 2, 1, 0, \rest], 2),
          \scale, a,
          \dur, 0.25
     );

     q = p.play;
})
)

Key

Key tracks key changes and modulations, so you can keep modulating or back out of modulations:

k = Key(Scale.choose);
k.scale.degrees;
k.scale.cents;
k.change(4); // modulate to the 5th scale degree (we start counting with 0)
k.scale.degrees;
k.scale.cents;
k.change; // go back

k.scale.degrees;

This will keep up through as many layers of modulations as you want.

It also does rounding:

quantizeFreq (freq, base, round , gravity )
Snaps the feq value in Hz to the nearest Hz value in the current key

gravity changes the level of attraction to the in tune frequency.

k.quantizeFreq(660, 440, \down, 0.5) // half way in tune

By changing gravity over time, you can have pitched tend towards being in or out of tune.

Scala

There is a huge library of pre-cooked tunings for the scala program. ( at http://www.huygens-fokker.org/scala/scl_format.html ) This class opens those files.

a = Scala("slendro.scl");
b = a.scale;

Lattice

This is actually a partchian tuning diamond (and this class may get a new name in a new release)

l = Lattice([ 2, 5, 3, 7, 9])

The array is numbers to use in generated tuning ratios, so this gives:

1/1 5/4 3/2 7/4 9/8   for otonality
1/1 8/5 4/3 8/7 16/9  for utonality

otonality is overtones – the numbers you give are in the numerator
utonality is undertones – the numbers are in denominator

all of the other numbers are powers of 2. You could change that with an optional second argument to any other number, such as 3:

l = Lattice([ 2, 3, 5, 7, 11], 3)

Lattices also generate a table:

1/1  5/4  3/2  7/4  9/8
8/5  1/1  6/5  7/5  9/5
4/3  5/3  1/1  7/6  3/2
8/7  10/7 12/7 1/1  9/7
16/9 10/9 4/3  14/9 1/1

It is possible to walk around this table to make nice triads that are harmonically related:

(
s.waitForBoot({

 var lat, orientation, startx, starty, baseFreq;

 SynthDef("sine", {arg out = 0, dur = 5, freq, amp=0.2, pan = 0;
  var env, osc;
  env = EnvGen.kr(Env.sine(dur, amp), doneAction: 2);
  osc = SinOsc.ar(freq, 0, env);
  Out.ar(out, osc * amp);
 }).add;

 s.sync;


 lat = Lattice.new;
 orientation = true;
 startx = 0;
 starty = 0;
 baseFreq = 440;

 Pbind(
  \instrument, \sine,
  \amp, 0.3,
  \freq, Pfunc({
   var starts, result;
     orientation = orientation.not;
     starts = lat.d3Pivot(startx, starty, orientation);
     startx = starts.first;
     starty = starts.last;
   result = lat.makeIntervals(startx, starty, orientation);
   (result * baseFreq)
  })
 ).play
})
)

Somewhat embarrassingly, I got confused between 2 and 3 dimensions when I wrote this code. A forthcoming version will have different method names, but the old ones will still be kept around so as not to break your code.

DissonanceCurve

This is not the only quark that does dissonance curves in SuperCollider.

Dissonance curves are used to compute tunings based on timbre, which is to say the spectrum.

d = DissonanceCurve([440], [1])
d.plot

The high part of the graph is highly dissonant and the low part is not dissonant. (The horizontal access is cents.) This is for just one pitch, but with additional pitches, the graph changes:

d = DissonanceCurve([335, 440], [0.7, 0.3])
d.plot

The combination of pitches produces a more complex graph with minima. Those minima are good scale steps.

This class is currently optimised for FM, but subsequent versions will calculate spectra for Ring Modulation, AM Modulation, Phase Modulation and combinations of all of those things.

(

s.waitForBoot({

 var carrier, modulator, depth, curve, scale, degrees;

 SynthDef("fm", {arg out, amp, carrier, modulator, depth, dur, midinote = 0;
  var sin, ratio, env;

  ratio = midinote.midiratio;
  carrier = carrier * ratio;
  modulator = modulator * ratio;
  depth = depth * ratio;

  sin = SinOsc.ar(SinOsc.ar(modulator, 0, depth, carrier));
  env = EnvGen.kr(Env.perc(releaseTime: dur)) * amp;
  Out.ar(out, (sin * env).dup);
 }).add;

 s.sync;

 carrier = 440;
 modulator = 600;
 depth = 100;
 curve = DissonanceCurve.fm(carrier, modulator, depth, 1200);
 scale = curve.scale;


 degrees = (0..scale.size); // make an array of all the scale degrees


// We don't know how many pitches per octave  will be until after the
// DissonanceCurve is calculated.  However, deprees outside of the range
// will be mapped accordingly.


 Pbind(

  \instrument, \fm,
  \octave, 0,
  \scale, scale,
  \degree, Pseq([
   Pseq(degrees, 1), // play one octave
   Pseq([-3, 2, 0, -1, 3, 1], 1) // play other notes
  ], 1),

  \carrier, carrier,
  \modulator, modulator,
  \depth, depth
 ).play
});
)

The only problem here is that this conflicts entirely with Just Intonation!

For just tunings based on spectra, we would calculate dissonance based on the ratios of the partials of the sound. Low numbers are more in tune, high numbers are less in tune.

There's only one problem with this: Here's a graph of just a sine tone:

d = DissonanceCurve([440], [1])
d.just_curve.collect({|diss| diss.dissonance}).plot

How do we pick tuning degrees?

We use a moving window where we pick the most consonant tuning within that window. This defaults to 100 cents, assuming you want something with roughly normal step sizes.

Then to pick scale steps, we can ask for the n most consonant tunings

t = d.digestibleScale(100, 7); // pick the 7 most consonant tunings
(
var carrier, modulator, depth, curve, scale, degrees;
carrier = 440;
modulator = 600;
depth = 100;
curve = DissonanceCurve.fm(carrier, modulator, depth, 1200);
scale = curve.digestibleScale(100, 7); // pick the 7 most consonant tunings
degrees = (0..(scale.size - 1)); // make an array of all the scale degrees (you can't assume the size is 7)

Pbind(
 \instrument, \fm,
 \octave, 0,
 \scale, scale,
 \degree, Pseq([
  Pseq(degrees, 1), // play one octave
  Pseq([-7, 2, 0, -5, 4, 1], 1)], 1), // play other notes
 \carrier, carrier,
 \modulator, modulator,
 \depth, depth
).play
)

Future plans

  • Update the help files!
  • Add the ability to calculate more spectra - PM, RM AM, etc
  • Make some of the method names more reasonable

Comments

Comments from the audience.

  • key - does it recalc the scale or not? Let the user decide
  • just dissonance curve - limit tuning ratios
  • lattice - make n dimensional
  • digestible scale - print scale ratios

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