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.
SyntaxEdit
var AudioParam = AudioParam.exponentialRampToValueAtTime(value, endTime)
Parameters
- value
- A floating point number representing the value the
AudioParamwill 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.
ExamplesEdit
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.
SpecificationsEdit
| Specification | Status | Comment |
|---|---|---|
| Web Audio API The definition of 'exponentialRampToValueAtTime' in that specification. |
Working Draft |