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The AudioParam
interface represents an audio-related parameter, usually a parameter of an AudioNode
(such as GainNode.gain
). An AudioParam
can be set to a specific value or a change in value, and can be scheduled to happen at a specific time and following a specific pattern.
There are two kinds of AudioParam
, a-rate and k-rate parameters:
- An a-rate
AudioParam
takes the current audio parameter value for each sample frame of the audio signal. - A k-rate
AudioParam
uses the same initial audio parameter value for the whole block processed, that is 128 sample frames.
Each AudioNode
defines which of its parameters are a-rate or k-rate in the spec.
Each AudioParam
has a list of events, initially empty, that define when and how values change. When this list is not empty, changes using the AudioParam.value
attributes are ignored. This list of events allows us to schedule changes that have to happen at very precise times, using arbitrary timelime-based automation curves. The time used is the one defined in AudioContext.currentTime
.
Properties
AudioParam
Inherits properties from its parent, AudioNode
.
AudioParam.defaultValue
Read only- Represents the initial volume of the attribute as defined by the specific
AudioNode
creating theAudioParam
. AudioParam.maxValue
Read only- Represents the maximum possible value for the parameter's nominal (effective) range.
AudioParam.minValue
Read only- Represents the minimum possible value for the parameter's nominal (effective) range.
AudioParam.value
- Represents the parameter's current volume as a floating point value; initially set to the value of
AudioParam.defaultValue
. Though it can be set, any modifications happening while there are automation events scheduled — that is events scheduled using the methods of theAudioParam
— are ignored, without raising any exception.
Methods
AudioParam Inherits methods from its parent, AudioNode
.
AudioParam.setValueAtTime()
- Schedules an instant change to the value of the
AudioParam
at a precise time, as measured againstAudioContext.currentTime
. The new value is given in thevalue
parameter. AudioParam.linearRampToValueAtTime()
- Schedules a gradual linear change in the value of the
AudioParam
. The change starts at the time specified for the previous event, follows a linear ramp to the new value given in thevalue
parameter, and reaches the new value at the time given in theendTime
parameter. AudioParam.exponentialRampToValueAtTime()
- Schedules a gradual exponential change in the value of the
AudioParam
. The change starts at the time specified for the previous event, follows an exponential ramp to the new value given in thevalue
parameter, and reaches the new value at the time given in theendTime
parameter. AudioParam.setTargetAtTime()
- Schedules the start of a change to the value of the
AudioParam
. The change starts at the time specified instartTime
and exponentially moves towards the value given by thetarget
parameter. The exponential decay rate is defined by thetimeConstant
parameter, which is a time measured in seconds. AudioParam.setValueCurveAtTime()
- Schedules the values of the
AudioParam
to follow a set of values, defined by thevalues
Float32Array
scaled to fit into the given interval, starting atstartTime
, and having a specificduration
. AudioParam.cancelScheduledValues()
- Cancels all scheduled future changes to the
AudioParam
.
Examples
First, a basic example showing a GainNode
having its gain
value set. gain
is an example of an a-rate AudioParam, as the value can potentially be set differently for each sample frame of the audio.
var AudioContext = window.AudioContext || window.webkitAudioContext; var audioCtx = new AudioContext(); var gainNode = audioCtx.createGain(); gainNode.gain.value = 0;
Next, an example showing a BiquadFilterNode
having some values set. These are examples of k-rate AudioParam's, as the values are set for the entire audio block at once.
var AudioContext = window.AudioContext || window.webkitAudioContext; var audioCtx = new AudioContext(); var biquadFilter = audioCtx.createBiquadFilter(); biquadFilter.type = "lowshelf"; biquadFilter.frequency.value = 1000; biquadFilter.gain.value = 25;
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'AudioParam' in that specification. |
Working Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 14.0 webkit | 23 (23) | No support | 15 webkit 22 (unprefixed) |
6 webkit |
Unprefixed | (Yes) | (Yes) | |||
minValue and maxValue |
52.0 | 39 |
Feature | Android | Android Webview | Firefox Mobile (Gecko) | Firefox OS | IE Phone | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | No support | (Yes) | 25.0 (25) | 1.2 | No support | No support | 6 webkit | 28.0 webkit |
Unprefixed | No support | (Yes) | (Yes) | (Yes) | ||||
minValue and maxValue |
No support | 52.0 | 39 | 52.0 |