AudioParam

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.value
Represents the parameter's current 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 the AudioParam — are ignored, without raising any exception.
AudioParam.defaultValue Read only
Represents the initial value of the attributes as defined by the specific AudioNode creating the AudioParam.

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 against AudioContext.currentTime. The new value is given in the value 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 the value parameter, and reaches the new value at the time given in the endTime 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 the value parameter, and reaches the new value at the time given in the endTime parameter.
AudioParam.setTargetAtTime()
Schedules the start of a change to the value of the AudioParam. The change starts at the time specified in startTime and exponentially moves towards the value given by the target parameter. The exponential decay rate is defined by the timeConstant parameter, which is a time measured in seconds.
AudioParam.setValueCurveAtTime()
Schedules the values of the AudioParam to follow a set of values, defined by the values Float32Array scaled to fit into the given interval, starting at startTime, and having a specific duration.
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 webkit 23 (23) Not supported 15 webkit
22 (unprefixed)
6 webkit
Feature Android Chrome Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support Not supported 28 webkit 25.0 (25) 1.2 Not supported Not supported webkit

See also

Document Tags and Contributors

Contributors to this page: fscholz, chrisdavidmills, padenot, teoli, kscarfone, Sheppy
Last updated by: fscholz,