AudioParam.setTargetAtTime()
The setTargetAtTime()
method of the AudioParam
Interface 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. This is the time it takes a first-order linear continuous time-invariant system to reach the value 1 - 1/e
(around 63.2%) given a step input response (transition from 0
to 1
value): basically, the larger it is, the slower the transition will be. This is useful for decay or release portions of envelopes.
Syntax
var AudioParam = AudioParam.setTargetAtTime(target, startTime, timeConstant)
Parameters
- target
- The value the parameter will start to transition towards at the given start time.
- startTime
- The time that the exponential transition will begin, which will be relative to
AudioContext.currentTime
. - timeConstant
- The time-constant value of first-order filter (exponential) approach to the target value. The larger this value is, the slower the transition will be.
Returns
A reference to this AudioParam
object. In some browsers older implementations of this interface return void.
Examples
In this example, we have a media source with two control buttons (see the audio-param repo for the source code, or view the example live.) When these buttons are pressed, setTargetAtTime()
is used to fade the gain value up to 1.0, and down to 0, respectively, with the effect starting after 1 second, and the length of time the effect lasts being controlled by the timeConstant (see the AudioParam interface section of the spec for an explanation of the maths behind this.)
// create audio context var AudioContext = window.AudioContext || window.webkitAudioContext; var audioCtx = new AudioContext(); // set basic variables for example var myAudio = document.querySelector('audio'); var pre = document.querySelector('pre'); var myScript = document.querySelector('script'); pre.innerHTML = myScript.innerHTML; var atTimePlus = document.querySelector('.at-time-plus'); var atTimeMinus = document.querySelector('.at-time-minus'); // Create a MediaElementAudioSourceNode // Feed the HTMLMediaElement into it var source = audioCtx.createMediaElementSource(myAudio); // Create a gain node and set it's gain value to 0.5 var gainNode = audioCtx.createGain(); gainNode.gain.value = 0.5; var currGain = gainNode.gain.value; // connect the AudioBufferSourceNode to the gainNode // and the gainNode to the destination source.connect(gainNode); gainNode.connect(audioCtx.destination); // set buttons to do something onclick atTimePlus.onclick = function() { currGain = 1.0; gainNode.gain.setTargetAtTime(1.0, audioCtx.currentTime + 1, 0.5); } atTimeMinus.onclick = function() { currGain = 0; gainNode.gain.setTargetAtTime(0, audioCtx.currentTime + 1, 0.5); }
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'setTargetAtTime' in that specification. |
Working Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 14 webkit | 23 | Not supported | 15 webkit 22 (unprefixed) |
6 webkit |
Unprefixed | (Yes) |
Feature | Android | Chrome | Firefox Mobile (Gecko) | Firefox OS | IE Phone | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | Not supported | ? | 25 | 1.2 | Not supported | Not supported | 6 webkit | 28 webkit |
Unprefixed | (Yes) | (Yes) |
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/audioparam/settargetattime