BaseAudioContext
The BaseAudioContext interface acts as a supervisor of audio-processing graphs. It provides key processing parameters such as current time, output destination or sample rate.
Additionally, it is responsible for nodes creation and audio-processing graph's lifecycle management.
However, BaseAudioContext itself cannot be directly utilized, instead its functionalities must be accessed through one of its derived interfaces: AudioContext, OfflineAudioContext.
Audio graph
An audio graph is a structured representation of audio processing elements and their connections within an audio context. The graph consists of various types of nodes, each performing specific audio operations, connected in a network that defines the audio signal flow. In general we can distinguish four types of nodes:
- Source nodes (e.g
AudioBufferSourceNode,OscillatorNode) - Effect nodes (e.g
GainNode,BiquadFilterNode) - Analysis nodes (e.g
AnalyserNode) - Destination nodes (e.g
AudioDestinationNode)
Rendering audio graph
Audio graph rendering is done in blocks of sample-frames. The number of sample-frames in a block is called render quantum size, and the block itself is called a render quantum. By default render quantum size value is 128 and it is constant.
The AudioContext rendering thread is driven by a system-level audio callback.
Each call has a system-level audio callback buffer size, which is a varying number of sample-frames that needs to be computed on time before the next system-level audio callback arrives,
but render quantum size does not have to be a divisor of the system-level audio callback buffer size.
Concept of system-level audio callback does not apply to OfflineAudioContext.
Properties
| Name | Type | Description | |
|---|---|---|---|
currentTime | number | Double value representing an ever-increasing hardware time in seconds, starting from 0. | Read only |
destination | AudioDestinationNode | Final output destination associated with the context. | Read only |
sampleRate | number | Float value representing the sample rate (in samples per seconds) used by all nodes in this context. | Read only |
state | ContextState | Enumerated value represents the current state of the context. | Read only |
Methods
createAnalyser
The above method lets you create AnalyserNode.
Returns AnalyserNode.
createBiquadFilter
The above method lets you create BiquadFilterNode.
Returns BiquadFilterNode.
createBuffer
The above method lets you create AudioBuffer.
| Parameters | Type | Description |
|---|---|---|
numOfChannels | number | An integer representing the number of channels of the buffer. |
length | number | An integer representing the length of the buffer in sampleFrames. Two seconds buffer has length equals to 2 * sampleRate. |
sampleRate | number | A float representing the sample rate of the buffer. |
Errors
| Error type | Description |
|---|---|
NotSupportedError | numOfChannels is outside the nominal range [1, 32]. |
NotSupportedError | sampleRate is outside the nominal range [8000, 96000]. |
NotSupportedError | length is less then 1. |
Returns AudioBuffer.
createBufferSource
The above method lets you create AudioBufferSourceNode.
| Parameters | Type | Description |
|---|---|---|
pitchCorrection Optional | AudioBufferSourceNodeOptions | Dictionary object that specifies if pitch correction has to be available. |
Returns AudioBufferSourceNode.
createGain
The above method lets you create GainNode.
Returns GainNode.
createOscillator
The above method lets you create OscillatorNode.
Returns OscillatorNode.
createPeriodicWave
The above method lets you create PeriodicWave.
| Parameters | Type | Description |
|---|---|---|
real | Float32Array | An array of cosine terms. |
imag | Float32Array | An array of sine terms. |
constraints Optional | PeriodicWaveConstraints | An object that specifies if normalization is disabled. |
Errors
| Error type | Description |
|---|---|
InvalidAccessError | real and imag arrays do not have same length. |
Returns PeriodicWave.
createStereoPanner
The above method lets you create StereoPannerNode.
Returns StereoPannerNode.
decodeAudioData
The above method lets you decode audio data. It decodes with in memory audio data block.
| Parameters | Type | Description |
|---|---|---|
arrayBuffer | ArrayBuffer | ArrayBuffer with audio data. |
Returns Promise<AudioBuffer>.
decodeAudioDataSource
The above method lets you decode audio data file. It saves file in the device file system.
| Parameters | Type | Description |
|---|---|---|
sourcePath | string | Path to audio file located on the device. |
Returns Promise<AudioBuffer>.
Remarks
currentTime
- Timer starts when context is created, stops when context is suspended.