1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
---
title: AudioParam
slug: Web/API/AudioParam
tags:
- API
- Audio
- AudioParam
- Interface
- NeedsTranslation
- Reference
- TopicStub
- Web Audio API
translation_of: Web/API/AudioParam
---
<p>{{APIRef("Web Audio API")}}</p>
<div>
<p>The <code>AudioParam</code> interface represents an audio-related parameter, usually a parameter of an {{domxref("AudioNode")}} (such as {{ domxref("GainNode.gain") }}). An <code>AudioParam</code> 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.</p>
</div>
<p>There are two kinds of <code>AudioParam</code>, <em>a-rate</em> and <em>k-rate</em> parameters:</p>
<ul>
<li id="a-rate">An <em>a-rate</em> <code>AudioParam</code> takes the current audio parameter value for each <a href="https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API/Basic_concepts_behind_Web_Audio_API#Audio_buffers.3A_frames.2C_samples_and_channels">sample frame</a> of the audio signal.</li>
<li id="k-rate">A <em>k-rate</em> <code>AudioParam</code> uses the same initial audio parameter value for the whole block processed, that is 128 sample frames.</li>
</ul>
<p>Each {{domxref("AudioNode")}} defines which of its parameters are <em>a-rate</em> or <em>k-rate</em> in the spec.</p>
<p>Each <code>AudioParam</code> has a list of events, initially empty, that define when and how values change. When this list is not empty, changes using the <code>AudioParam.value</code> 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 {{domxref("AudioContext.currentTime")}}.</p>
<h2 id="Properties">Properties</h2>
<p><code>AudioParam</code><em> Inherits properties from its parent, </em><code>AudioNode</code>.</p>
<dl>
<dt>{{domxref("AudioParam.defaultValue")}} {{readonlyInline}}</dt>
<dd>Represents the initial volume of the attribute as defined by the specific {{domxref("AudioNode")}} creating the <code>AudioParam</code>.</dd>
<dt>{{domxref("AudioParam.maxValue")}} {{readonlyInline}}</dt>
<dd>Represents the maximum possible value for the parameter's nominal (effective) range. </dd>
<dt>{{domxref("AudioParam.minValue")}} {{readonlyinline}}</dt>
<dd>Represents the minimum possible value for the parameter's nominal (effective) range. </dd>
<dt>{{domxref("AudioParam.value")}}</dt>
<dd>Represents the parameter's current volume as a floating point value; initially set to the value of <code>AudioParam.defaultValue</code>. Though it can be set, any modifications happening while there are automation events scheduled — that is events scheduled using the methods of the <code>AudioParam</code> — are ignored, without raising any exception.</dd>
</dl>
<h2 id="Methods">Methods</h2>
<p>AudioParam<em> Inherits methods from its parent, </em><code>AudioNode</code>.</p>
<dl>
<dt>{{domxref("AudioParam.setValueAtTime()")}}</dt>
<dd>Schedules an instant change to the value of the <code>AudioParam</code> at a precise time, as measured against {{domxref("AudioContext.currentTime")}}. The new value is given in the <code>value</code> parameter.</dd>
<dt>{{domxref("AudioParam.linearRampToValueAtTime()")}}</dt>
<dd>Schedules a gradual linear change in the value of the <code>AudioParam</code>. The change starts at the time specified for the <em>previous</em> event, follows a linear ramp to the new value given in the <code>value</code> parameter, and reaches the new value at the time given in the <code>endTime</code> parameter.</dd>
<dt>{{domxref("AudioParam.exponentialRampToValueAtTime()")}}</dt>
<dd>Schedules a gradual exponential change in the value of the <code>AudioParam</code>. The change starts at the time specified for the <em>previous</em> event, follows an exponential ramp to the new value given in the <code>value</code> parameter, and reaches the new value at the time given in the <code>endTime</code> parameter.</dd>
<dt>{{domxref("AudioParam.setTargetAtTime()")}}</dt>
<dd>Schedules the start of a change to the value of the <code>AudioParam</code>. The change starts at the time specified in <code>startTime</code> and exponentially moves towards the value given by the <code>target</code> parameter. The exponential decay rate is defined by the <code>timeConstant</code> parameter, which is a time measured in seconds.</dd>
<dt>{{domxref("AudioParam.setValueCurveAtTime()")}}</dt>
<dd>Schedules the values of the <code>AudioParam</code> to follow a set of values, defined by the <code>values</code> {{domxref("Float32Array")}} scaled to fit into the given interval, starting at <code>startTime</code>, and having a specific <code>duration</code>.</dd>
<dt>{{domxref("AudioParam.cancelScheduledValues()")}}</dt>
<dd>Cancels all scheduled future changes to the <code>AudioParam</code>.</dd>
<dt>{{domxref("AudioParam.cancelAndHoldAtTime()")}}</dt>
<dd>Cancels all scheduled future changes to the <code>AudioParam</code> but holds its value at a given time until further changes are made using other methods. The new value is given in the <code>value</code> parameter.</dd>
</dl>
<h2 id="Examples">Examples</h2>
<p>First, a basic example showing a {{domxref("GainNode")}} having its <code>gain</code> value set. <code>gain</code> is an example of an a-rate AudioParam, as the value can potentially be set differently for each sample frame of the audio.</p>
<pre class="brush: js;highlight[5]">var AudioContext = window.AudioContext || window.webkitAudioContext;
var audioCtx = new AudioContext();
var gainNode = audioCtx.createGain();
gainNode.gain.value = 0;</pre>
<p>Next, an example showing a {{ domxref("BiquadFilterNode") }} having some values set. These are examples of k-rate AudioParam's, as the values are set for the entire audio block at once.</p>
<pre class="brush: js;highlight[6,7,8]">var AudioContext = window.AudioContext || window.webkitAudioContext;
var audioCtx = new AudioContext();
var biquadFilter = audioCtx.createBiquadFilter();
biquadFilter.type = "lowshelf";
biquadFilter.frequency.value = 1000;
biquadFilter.gain.value = 25;</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('Web Audio API', '#the-audioparam-interface', 'AudioParam')}}</td>
<td>{{Spec2('Web Audio API')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>{{CompatibilityTable}}</div>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Edge</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari (WebKit)</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatChrome(14)}} {{property_prefix("webkit")}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatGeckoDesktop(23)}}</td>
<td>{{CompatNo}}</td>
<td>15 {{property_prefix("webkit")}}<br>
22 (unprefixed)</td>
<td>6 {{property_prefix("webkit")}}</td>
</tr>
<tr>
<td>Unprefixed</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatNo}}</td>
</tr>
<tr>
<td><code>minValue</code> and <code>maxValue</code></td>
<td>{{CompatChrome(52)}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatNo}}</td>
<td>39</td>
<td>{{CompatNo}}</td>
</tr>
<tr>
<td><code>cancelAndHoldAtTime()</code></td>
<td>{{CompatChrome(57)}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android Webview</th>
<th>Chrome for Android</th>
<th>Edge</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Phone</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatChrome(28)}} {{property_prefix("webkit")}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatGeckoMobile(25)}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>6 {{property_prefix("webkit")}}</td>
</tr>
<tr>
<td>Unprefixed</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatNo}}</td>
</tr>
<tr>
<td><code>minValue</code> and <code>maxValue</code></td>
<td>{{CompatChrome(52)}}</td>
<td>{{CompatChrome(52)}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatNo}}</td>
<td>39</td>
<td>{{CompatNo}}</td>
</tr>
<tr>
<td><code>cancelAndHoldAtTime()</code></td>
<td>{{CompatChrome(57)}}</td>
<td>{{CompatChrome(57)}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
</tr>
</tbody>
</table>
</div>
<h2 id="See_also">See also</h2>
<ul>
<li><a href="/en-US/docs/Web_Audio_API/Using_Web_Audio_API">Using the Web Audio API</a></li>
</ul>
|
