The exponentialRampToValueAtTime()
method of the AudioParam
Interface 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.
Note: Exponential ramps are considered more useful when changing frequencies or playback rates than linear ramps because of the way the human ear works.
Syntax
var AudioParam = AudioParam.exponentialRampToValueAtTime(value, endTime)
Parameters
- value
- A floating point number representing the value the
AudioParam
will ramp to by the given time. - endTime
- A double representing the exact time (in seconds) after the ramping starts that the changing of the value will stop.
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, exponentialRampToValueAtTime()
is used to fade the gain value up to 1.0, and down to 0, respectively. This is pretty useful for fade in/fade out effects:
// 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 expRampPlus = document.querySelector('.exp-ramp-plus'); var expRampMinus = document.querySelector('.exp-ramp-minus'); // Create a MediaElementAudioSourceNode // Feed the HTMLMediaElement into it var source = audioCtx.createMediaElementSource(myAudio); // Create a gain node and set its 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 expRampPlus.onclick = function() { currGain = 1.0; gainNode.gain.exponentialRampToValueAtTime(1.0, audioCtx.currentTime + 2); } expRampMinus.onclick = function() { currGain = 0.01; gainNode.gain.exponentialRampToValueAtTime(0.01, audioCtx.currentTime + 2); }
Note: A value of 0.01 was used for the value to ramp down to in the last function rather than 0, as an invalid or illegal string error is thrown if 0 is used — the value needs to be positive.
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'exponentialRampToValueAtTime' 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) |