AudioParam.linearRampToValueAtTime() - Web APIs 编辑

The linearRampToValueAtTime() method of the AudioParam Interface 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.

Syntax

var AudioParam = AudioParam.linearRampToValueAtTime(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.

Example

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, linearRampToValueAtTime() 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, although AudioParam.exponentialRampToValueAtTime() is often said to be a bit more natural.

// 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 linearRampPlus = document.querySelector('.linear-ramp-plus');
var linearRampMinus = document.querySelector('.linear-ramp-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();

// connect the AudioBufferSourceNode to the gainNode
// and the gainNode to the destination
gainNode.gain.setValueAtTime(0, audioCtx.currentTime);
source.connect(gainNode);
gainNode.connect(audioCtx.destination);

// set buttons to do something onclick
linearRampPlus.onclick = function() {
  gainNode.gain.linearRampToValueAtTime(1.0, audioCtx.currentTime + 2);
}

linearRampMinus.onclick = function() {
  gainNode.gain.linearRampToValueAtTime(0, audioCtx.currentTime + 2);
}

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using the Web Audio API