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, i_dur=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: i_dur, 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, \i_dur, dur * durDiff ] );

durDiff.do({

Synth( "Help-SPE2", [ \freq, streams.at(1).next, \i_dur, dur ] );

dur.wait;

});

})

}).play

)

To go to the next file:

Streams-Patterns-Events3