Dynamic Audio Synthesis

on the Flash/Flex Platform

Joe Berkovitz

Overview

• Bit o’ background

• Flash 9 sound capabilities

• The Flash 10 Sound API

• StandingWave audio synthesis library

• New avenues for Flash audio and music

About me

Samples ‘n’ frames ‘n’ acoustics

Player 9 Sound API

• Sound objects can be loaded from URLs...

• ...or embedded as assets

• Load ‘em, play ‘em, change volume or stereo pan – that’s about it!

• Unpredictable latency, synchronization

Player 9 Audio// loading a sound over the networkvar s:Sound = new Sound();s.addEventListener(Event.COMPLETE, handleComplete);s.load(new URLRequest(“TheBomb.mp3”);

function handleComplete(e:Event) { Sound(event.target).play();}

Player 9 Audio// loading a sound from a library asset[Embed(source=”TheBomb.mp3”)]private static var MySoundAsset:Class;

function playSound():void{ var s:Sound = new MySoundAsset(); var sc:SoundChannel = s.play(); sc.soundTransform = new SoundTransform(0.5 /*volume*/); // set other transform properties... // examine playback position trace(sc.position);}

What we want to do...

• Dynamically compute sounds from scratch

• Process samples on the fly to shift pitch, add effects, equalization...

• Play more than 32 sounds at the same time

• Compute continuous sound output

FP10 to the rescue

• Synchronization and continuity: SAMPLES_CALLBACK event

• Access to codecs: Sound.extract()

• The Vector data type

• Adobe Pixel Bender runtime

• Alchemy

Dynamic Audio Outputvar s:Sound = new Sound();s.addEventListener(SampleDataEvent.SAMPLE_DATA, handleSampleData);var sc:SoundChannel = s.play();

function handleSampleData(e:SampleDataEvent) { for (i = 0; i < /*number of frames*/ ; i++) { e.data.writeFloat(/* left channel */); e.data.writeFloat(/* right channel */); }}

Codec Access[Embed(source=”TheBomb.mp3”)]private static var MySoundAsset:Class;

function getSoundSamples(numFrames:uint):void{ var s:Sound = new MySoundAsset(); var bytes:ByteArray = new ByteArray(); s.extract(bytes, numFrames, _position);

bytes.position = 0; for (var i:Number = 0; i < numFrames; i++) { ... = bytes.readFloat(); // Left channel ... = bytes.readFloat(); // Right channel }}

Some things to know

• Between 2048 and 8192 samples per event

• The fewer samples you provide, the lower the latency (time before a sample is heard)

• Initial latency > steady-state latency

• More samples/callback = more stability

• Don’t take too long to generate samples!

Basic Audio Demo

Going beyond theFP10 sound API

• Goal: to work at a higher level than samples

• High level concepts: Sources, Filters

• Play back timed, overlapping sequences of sonic or musical events: Performances

• Create a modular, extensible system

The StandingWave Project

• Open source AS3 library

• Outgrowth of Noteflight

• Requires Player 10

• Enables new class of audio applications

Audio Processing Concepts

Sample

Descriptor: 44.1 kHz Stereo

left[0]

left[1]

left[2]

left[3]

right[0]

right[1]

right[2]

right[3]

... ...

SampleSample

Audio Processing Concepts

AudioPlayerSource

raw samples,algorithms...

Samples

Audio Processing Concepts

AudioPlayerFilterSource

transformations

SampleSampleSamplesSampleSampleSamples

Audio Processing Concepts

Filter

AudioPlayer

Source

FilterSource

FilterSource

Perf

orm

ance

starts at 0.0 sec

starts at 0.2 sec

starts at 0.7 sec

(...continues...)

timed sequenceof sounds

Audio Processing Concepts

Filter

AudioPlayer

Source

FilterSource

FilterSource

Perf

orm

ance

starts at 0.0 sec

starts at 0.2 sec

starts at 0.7 sec

...

AudioPerformer

SampleSampleSamples

SampleSampleSamples

Audio Processing Concepts

Filter AudioPlayer

Source

FilterSource

FilterSource

Perf

orm

ance

starts at 0.0 sec

starts at 0.2 sec

starts at 0.7 sec

(...continues...)

FilterAudioPerformer

IAudioSourcepublic interface IAudioSource{ function get descriptor():AudioDescriptor; function get frameCount():Number;

function get position():Number; function resetPosition():void;

function getSample(numFrames:Number):Sample;

function clone():IAudioSource;} implementations: Sample, SineSource, SoundSource...

IAudioFilterpublic interface IAudioFilter extends IAudioSource{ function get source():IAudioSource; function set source(s:IAudioSource):void;} implementations: EnvelopeFilter, EchoFilter, BandpassFilter...

IPerformancepublic interface IPerformance{ function getElementsInRange (start:Number, end:Number) :Vector.<PerformanceElement>;} implementations: ListPerformance...

Noteflight: A Music Notation Editor

in Flash

What’s missing?

• Direct microphone input

• More codec libraries

• Fully functional and supported audio processing in PixelBender/Alchemy

Where to get the StandingWave library

http://code.google.com/p/standingwave

Places and Projects

http://joeberkovitz.com

http://www.hobnox.com

http://labs.adobe.com/wiki/index.php/Alchemy:Libraries

http://www.getmicrophone.com/

http://void.andre-michelle.com