Understanding Streams, Patterns and Events - Part 2
Patterns
Often one wants to be able to create multiple streams from a single stream specification. Patterns are just a way to make multiple Streams from a single specification, like a cookie cutter. A pattern can be any object that responds to the asStream message by creating a Stream. Once again there is a default implementation in class Object of asStream that simply returns the receiver as its own stream. Thus any object is by default a pattern that returns itself as a stream when sent the asStream message.
(
a = 7.asStream;
a.postln;
a.next.postln;
)
Pattern and its subclasses
There is a class named Pattern that provides more functionality for the concept of a pattern.
Pfunc is a Pattern that returns a FuncStream. The same function arguments are supplied as are supplied to FuncStream.
(
var a, b;
a = Pfunc.new({ #[1, 2, 3, 4].choose });
b = a.asStream; // make a stream from the pattern
5.do({ b.next.postln; }); // print 5 values from the stream
)
Prout is a Pattern that returns a Routine. The same function argument is supplied as is supplied to Routine.
(
var a, b, c;
a = Prout.new({
3.do({ arg i; 3.rand.yield; })
});
// make two streams from the pattern
b = a.asStream;
c = a.asStream;
4.do({ b.next.postln; }); // print 4 values from first stream
4.do({ c.next.postln; }); // print 4 values from second stream
)
Pseries is a Pattern that generates an arithmetic series.
(
var a, b;
a = Pseries.new(10, 3, 8); // stream starts at 10, steps by 3 and has length 8
b = a.asStream;
9.do({ b.next.postln; }); // print 9 values from stream
)
Pgeom is a Pattern that generates a geometric series.
(
var a, b;
// stream starts at 10, steps by factor of 3 and has length 8
a = Pgeom.new(10, 3, 8);
b = a.asStream;
9.do({ b.next.postln; }); // print 9 values from stream
)
Math operations on Patterns
Patterns also respond to math operators by returning patterns that respond to asStream with appropriately modified streams.
Applying a unary operator to a pattern
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
b = a.squared; // pattern b is a square of the pattern a
c = b.asStream;
12.do({ c.next.postln; });
)
Using a binary operator on a pattern
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
b = a + 100; // add a constant value to pattern a
c = b.asStream;
12.do({ c.next.postln; });
)
Filtering operations on patterns
Patterns also respond to the messages collect, select, and reject by returning a new Pattern.
The collect message returns a Pattern whose Stream is modified by a function in the same way as the collect message sent to a Collection returns a modified Collection.
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
// b is a pattern whose stream adds 100 to even values
b = a.collect({ arg item; if (item.even, { item + 100 },{ item }); });
c = b.asStream;
6.do({ c.next.postln; });
)
The select message creates a pattern whose stream passes only items that return true from a user supplied function.
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
// b is a pattern whose stream only returns the odd values
b = a.select({ arg item; item.odd; });
c = b.asStream;
6.do({ c.next.postln; });
)
The reject message creates a pattern whose stream passes only items that return false from a
user supplied function.
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
// b is a pattern whose stream that only returns the non-odd values
b = a.reject({ arg item; item.odd; });
c = b.asStream;
6.do({ c.next.postln; });
)
Making Music with Patterns
Here is a variation of the example given in part 1 that uses a Pattern to create two instances of the random melody stream.
(
s = Server.local;
SynthDef(\help_SPE2, { arg i_out=0, sustain=1, freq;
var out;
out = RLPF.ar(
LFSaw.ar( freq ),
LFNoise1.kr(1, 36, 110).midicps,
0.1
) * EnvGen.kr( Env.perc, levelScale: 0.3,
timeScale: sustain, doneAction: 2 );
//out = [out, DelayN.ar(out, 0.04, 0.04) ];
4.do({ out = AllpassN.ar(out, 0.05, [0.05.rand, 0.05.rand], 4) });
Out.ar( i_out, out );
}).send(s);
)
(
// streams as a sequence of pitches
var pattern, streams, dur, durDiff;
dur = 1/7;
durDiff = 3;
pattern = Prout.new({
loop({
if (0.5.coin, {
#[ 24,31,36,43,48,55 ].do({ arg fifth; fifth.yield });
});
rrand(2,5).do({
// varying arpeggio
60.yield;
#[63,65].choose.yield;
67.yield;
#[70,72,74].choose.yield;
});
// random high melody
rrand(3,9).do({ #[74,75,77,79,81].choose.yield });
});
});
streams = [
(pattern - Pfunc.new({ #[12, 7, 7, 0].choose })).midicps.asStream,
pattern.midicps.asStream
];
Routine({
loop({
Synth( \help_SPE2, [ \freq, streams.at(0).next, \sustain, dur * durDiff ] );
durDiff.do({
Synth( \help_SPE2, [ \freq, streams.at(1).next, \sustain, dur ] );
dur.wait;
});
})
}).play
)
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