AudioParam | Web API

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The Web Audio API's AudioParam interface represents an audio-related parameter, usually a parameter of an AudioNode (譬如 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. In other words, the same value applies to every frame in the audio as it's processed by the node.

每个 AudioNode defines which of its parameters are a-rate or k-rate in the spec.

每个 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 .

特性

AudioParam.defaultValue 只读: Represents the initial volume of the attribute as defined by the specific AudioNode creating the AudioParam .
AudioParam.maxValue 只读
AudioParam.minValue 只读
AudioParam.value: Represents the parameter's current value as of the current time; initially set to the value of defaultValue .

方法

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 by the value 参数。
AudioParam.linearRampToValueAtTime(): Schedules a gradual linear change in the value of the AudioParam . The change starts at the time specified for the 上一 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 参数。
AudioParam.exponentialRampToValueAtTime(): Schedules a gradual exponential change in the value of the AudioParam . The change starts at the time specified for the 上一 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 参数。
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 an array of floating-point numbers scaled to fit into the given interval, starting at a given start time and spanning a given duration of time.
AudioParam.cancelScheduledValues(): Cancels all scheduled future changes to the AudioParam .
AudioParam.cancelAndHoldAtTime(): Cancels all scheduled future changes to the AudioParam but holds its value at a given time until further changes are made using other methods.

范例

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 DynamicsCompressorNode having some param values maniuplated. These are examples of k-rate AudioParam's, as the values are set for the entire audio block at once.

var compressor = audioCtx.createDynamicsCompressor();
compressor.threshold.setValueAtTime(-50, audioCtx.currentTime);
compressor.knee.setValueAtTime(40, audioCtx.currentTime);
compressor.ratio.setValueAtTime(12, audioCtx.currentTime);
compressor.attack.setValueAtTime(0, audioCtx.currentTime);
compressor.release.setValueAtTime(0.25, audioCtx.currentTime);

规范

规范	状态	注释
Web 音频 API The definition of 'AudioParam' in that specification.	工作草案

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`AudioParam`	Chrome 14	Edge ≤18	Firefox 25	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`automationRate`	Chrome 68	Edge ≤79	Firefox ?	IE 不支持 No	Opera Yes	Safari ?	WebView Android 68	Chrome Android 68	Firefox Android ?	Opera Android Yes	Safari iOS Yes	Samsung Internet Android 10.0
`cancelAndHoldAtTime`	Chrome 57 57 ? — 56 Alternate Name Alternate Name Uses the non-standard name: `cancelValuesAndHoldAtTime()`	Edge ≤79	Firefox 不支持 No	IE 不支持 No	Opera 44 44 ? — 43 Alternate Name Alternate Name Uses the non-standard name: `cancelValuesAndHoldAtTime()`	Safari 不支持 No	WebView Android 57 57 ? — 56 Alternate Name Alternate Name Uses the non-standard name: `cancelValuesAndHoldAtTime()`	Chrome Android 57 57 ? — 56 Alternate Name Alternate Name Uses the non-standard name: `cancelValuesAndHoldAtTime()`	Firefox Android 不支持 No	Opera Android 43 43 ? — 43 Alternate Name Alternate Name Uses the non-standard name: `cancelValuesAndHoldAtTime()`	Safari iOS 不支持 No	Samsung Internet Android 7.0 7.0 ? — 6.0 Alternate Name Alternate Name Uses the non-standard name: `cancelValuesAndHoldAtTime()`
`cancelScheduledValues`	Chrome 14	Edge 12	Firefox 25	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`defaultValue`	Chrome 14	Edge 12	Firefox 25	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`exponentialRampToValueAtTime`	Chrome 14	Edge 12	Firefox 部分支持 25 注意事项部分支持 25 注意事项 Does not work (see bug 1171438 and bug 1567777 ).	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 部分支持 18 注意事项部分支持 18 注意事项 This sets the target volume at the specified time, but it doesn’t ramp to it, causing this function to behave like `setValueAtTime()` .	Firefox Android 部分支持 26 注意事项部分支持 26 注意事项 Does not work (see bug 1171438 and bug 1567777 ).	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`linearRampToValueAtTime`	Chrome 14	Edge 12	Firefox 部分支持 25 注意事项部分支持 25 注意事项 Does not work (see bug 1171438 and bug 1567777 ).	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 部分支持 18 注意事项部分支持 18 注意事项 This sets the target volume at the specified time, but it doesn’t ramp to it, causing this function to behave like `setValueAtTime()` .	Firefox Android 部分支持 26 注意事项部分支持 26 注意事项 Does not work (see bug 1171438 and bug 1567777 ).	Opera Android 14	Safari iOS ?	Samsung Internet Android 1.0
`maxValue`	Chrome 52	Edge ≤18	Firefox 53	IE 不支持 No	Opera 39	Safari 6	WebView Android 52	Chrome Android 52	Firefox Android 53	Opera Android 41	Safari iOS Yes	Samsung Internet Android 6.0
`minValue`	Chrome 52	Edge ≤18	Firefox 53	IE 不支持 No	Opera 39	Safari 6	WebView Android 52	Chrome Android 52	Firefox Android 53	Opera Android 41	Safari iOS Yes	Samsung Internet Android 6.0
`setTargetAtTime`	Chrome 14	Edge 12	Firefox 25	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`setValueAtTime`	Chrome 14	Edge 12	Firefox 25	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`setValueCurveAtTime`	Chrome 14	Edge 12	Firefox 25	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0
`value`	Chrome 14	Edge 12	Firefox 25 注意事项 25 注意事项 Prior to Firefox 69, `value` did not take into account scheduled or gradiated changes to the parameter's value; instead, only explicitly set values were returned.	IE 不支持 No	Opera 15	Safari 6	WebView Android Yes	Chrome Android 18	Firefox Android 26 注意事项 26 注意事项 Firefox for Android does not currently take into account scheduled or gradiated changes to the parameter's value; only the initial value or the most recent explicitly set value is returned.	Opera Android 14	Safari iOS Yes	Samsung Internet Android 1.0

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最后修改： May 17, 2020

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