AudioIO.jl

AudioIO is a Julia library for interfacing to audio streams, which include playing to and recording from sound cards, reading and writing audio files, sending to network audio streams, etc. Currently only playing to the sound card through PortAudio is supported. It is under heavy development, so the API could change, there will be bugs, there are important missing features.

Installation

To install the latest release version, simply run

julia> Pkg.add("AudioIO")

If you want to install the lastest master, it's almost as easy:

julia> Pkg.clone("AudioIO")
julia> Pkg.build("AudioIO")

Basic Array Playback

Arrays in various formats can be played through your soundcard. Currently the native format that is delivered to the PortAudio backend is Float32 in the range of [-1, 1]. Arrays in other sizes of float are converted. Arrays in Signed or Unsigned Integer types are scaled so that the full range is mapped to [-1, 1] floating point values.

To play a 1-second burst of noise:

julia> v = rand(44100) * 0.1
julia> play(v)

AudioNodes

In addition to the basic play function you can create more complex networks of AudioNodes in a render chain. In fact, when using the basic play to play an Array, behind the scenes an instance of the ArrayPlayer type is created and added to the master AudioMixer inputs. Audionodes also implement a stop function, which will remove them from the render graph. When an implicit AudioNode is created automatically, such as when using play on an Array, the play function should return the audio node that is playing the Array, so it can be stopped if desired.

To explictly do the same as above:

julia> v = rand(44100) * 0.1
julia> player = ArrayPlayer(v)
julia> play(player)

To generate 2 sin tones:

julia> osc1 = SinOsc(440)
julia> osc2 = SinOsc(660)
julia> play(osc1)
julia> play(osc2)
julia> stop(osc1)
julia> stop(osc2)

All AudioNodes must implement a render function that can be called to retreive the next block of audio.

AudioStreams

AudioStreams represent an external source or destination for audio, such as the sound card. The play function attaches AudioNodes to the default stream unless a stream is given as the 2nd argument.

AudioStream is an abstract type, which currently has a PortAudioStream subtype that writes to the sound card, and a TestAudioStream that is used in the unit tests.

Currently only 1 stream at a time is supported so there's no reason to provide an explicit stream to the play function. The stream has a root mixer field which is an instance of the AudioMixer type, so that multiple AudioNodes can be heard at the same time. Whenever a new frame of audio is needed by the sound card, the stream calls the render method on the root audio mixer, which will in turn call the render methods on any input AudioNodes that are set up as inputs.