AudioParam
The Web Audio API's AudioParam
interface represents an audio-related parameter, usually a parameter of an AudioNode
(such as 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.
Each 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 timeline-based automation curves. The time used is the one defined in AudioContext.currentTime
.
AudioParam types
There are two AudioParam
kinds: a-rate and k-rate parameters. Each AudioNode
defines which of its parameters are a-rate or k-rate in the spec.
a-rate
An a-rate AudioParam
takes the current audio parameter value for each sample frame of the audio signal.
k-rate
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.
Instance properties
AudioParam.defaultValue
Read only-
Represents the initial value of the attribute as defined by the specific
AudioNode
creating theAudioParam
. AudioParam.maxValue
Read only-
Represents the maximum possible value for the parameter's nominal (effective) range.
AudioParam.minValue
Read only-
Represents the minimum possible value for the parameter's nominal (effective) range.
AudioParam.value
-
Represents the parameter's current value as of the current time; initially set to the value of
defaultValue
.
Instance methods
AudioParam.setValueAtTime()
-
Schedules an instant change to the value of the
AudioParam
at a precise time, as measured againstAudioContext.currentTime
. The new value is given by thevalue
parameter. AudioParam.linearRampToValueAtTime()
-
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 thevalue
parameter, and reaches the new value at the time given in theendTime
parameter. AudioParam.exponentialRampToValueAtTime()
-
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 thevalue
parameter, and reaches the new value at the time given in theendTime
parameter. AudioParam.setTargetAtTime()
-
Schedules the start of a change to the value of the
AudioParam
. The change starts at the time specified instartTime
and exponentially moves towards the value given by thetarget
parameter. The exponential decay rate is defined by thetimeConstant
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.
Examples
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.
js
const audioCtx = new AudioContext();
const gainNode = audioCtx.createGain();
gainNode.gain.value = 0;
Next, an example showing a DynamicsCompressorNode
having some param values manipulated. These are examples of k-rate AudioParam
types, as the values are set for the entire audio block at once.
js
const 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);
Specifications
Specification |
---|
Web Audio API # AudioParam |
Browser compatibility
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