Download - NoiseGen at Arlington Ruby 2012
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Let's build a software synthesizerin about 20 40 minutes.
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Digital Sound
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Exercises for reader:
Speakers → Ears → Consciousness
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Let's start with speakers
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Sideways is even better
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Alternating Current
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Sound = Speaker movement = Electrical input
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Waves
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digital?
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Divide into samples
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A sample is number from -1 .. 1
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(y-axis)
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Evenly spaced over time
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(x-axis)
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Samples per second
↳ "Sample Rate"
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Common sample rates:
DVD: 48,000CD: 44,100VOIP: 16,000Telephone: 8,000
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Representation of each sample
↳ "Bit Depth"
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8 bit: 0..255 (old video games)
16 bit: 0..65535 (CD)
24 bit: 0..16777215 (DVD-Audio)
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Human Ear: 21 bit @ 40k
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Volume (amplitude) and Frequency
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Volume is easy!
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Frequency not so easy
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frequency = wiggle speed = pitch
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Low bit depthcauses volume-aliasing
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Low sample ratecauses frequency-aliasing
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So!
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We just gotta generate and play samples!
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44100 of them per second!
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No problem.
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PortAudio
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Alternatives: /dev/dsp, aplay, ...
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PortAudio.init
stream = PortAudio::Stream.open( :sample_rate => 44100, :frames => 512, :output => { :device => PortAudio::Device.default_output, :channels => 1, :sample_format => :float32 })
stream.start
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buffer = PortAudio::SampleBuffer.new( :format => :float32, :channels => 1, :frames => 512)
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# smallnoise.rb
loop do buffer.fill { rand()*2 - 1 # From -1 .. 1 } stream << bufferend
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Woo... static!
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sample = rand()*2 - 1
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# smallbeep.rb
time_step = 1 / 48000.0time = 0.0loop do buffer.fill { time += time_step; Math.sin( 2 * 3.1415 * time * 440 ); } stream << bufferend
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Woo... beeping!
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Two beeps at once?
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Turns out you just add waves together
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# smallbeep2.rb
sample = Math.sin( 2 * 3.1415 * time * 440 );sample += Math.sin( 2 * 3.1415 * time * 349.23 );sample /= 2; # Avoid clipping!
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Let's generalize
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sample = get_next_sample();
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Call get_next_sample() over and over
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Get a new sample each time
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def sine { Math.sin( 2 * 3.1415 * $time * 440 )}
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That was easy.
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Not very configurable or dynamic though.
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# What I want:
sample_gen = sine(440);
# ...
sample = sample_gen.call;
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This is called a 'generator'
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We can make this using a closure!
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(aka lambda with bound variables)
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def sine(freq) lambda { Math.sin( 2 * 3.1415 * $time * freq ); }}
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# So now we have it:
sample_gen = sine(440);
# ... in 'play'
sample = sample_gen.call;
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# Create a 440 Hz sine generatorgen = sine(440);
# Play it!play( gen );
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play( sine( 440 ) );
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One more generator tweak
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Parameterize generators with generators,and use named params
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sub sine(freq) { freq = genize freq lambda { Math.sin( 2 * 3.1415 * $time * freq.call ); }}
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# Take a parameter and ensure it is a generator.# If it is already a generator leave it alone,# otherwise wrap it up so that it *is* a generator.
def genize x if x.is_a?(Proc) return x end lambda { x }end
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Why would we use generatorsas parameters?
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lfo = sine(5)wobble_freq = lambda { lfo.call * 100 + 440 }
play( sine( wobble_freq ) );
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Now we're cooking with FIRE!
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Plays forever...
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Envelope Generator
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Attack, [Decay], Sustain, Release
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envelope( gen, attack, sustain, release )
# For example
envelope( sine(440), 2, 0, 2 )
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returns nil when done
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Sequence Generator
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seq( gens )
# For example
play( seq([ envelope(square(440), 2, 0, 2), envelope(square(220), 2, 0, 2), ]))
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Simultaneous Generators Generator
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play( sum([ envelope(square(440), 2, 0, 2), envelope(square(220), 2, 0, 2), envelope(square(880), 2, 0, 2), envelope(square(660), 2, 0, 2), ]))
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Let's build something we can PLAY
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Input Control Generator
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Using my touch-screen
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$ xmousepos838 574 221 170
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x = `xmousepos`.split[0];
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def mousefreq() count = 0 x = 0.0 lambda { count += 1 if count % 1000 == 0 x = `xmousepos`.split[0].to_f end x }end
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play( amp( sine( mousefreq() ), mousevol() ));
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And now we have a synth :)
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THE END
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References
Source Code:http://thelackthereof.org/NoiseGenhttp://github.com/awwaiid/ruby-noise
Digital fidelity discussion:http://people.xiph.org/~xiphmont/demo/neil-young.html
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BONUS SLIDES
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Note / Song Generators
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note( 'A4' )
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segment( 'A4 F3' ),
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combine([ segment( 'A4' ), segment( 'F3' ),])
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Formula-Based Noisehttp://countercomplex.blogspot.com/2011/10/algorithmic-symphonies-from-one-line-of.html