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Audio: add fadeIn & fadeOut #32549

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Audio: add fadeIn & fadeOut #32549

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48 changes: 48 additions & 0 deletions src/audio/Audio.js
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Original file line number Diff line number Diff line change
Expand Up @@ -736,6 +736,35 @@ class Audio extends Object3D {

}

/**
* Fades the audio in by increasing volume gradually from `volumeNow` to `volumeThen`,
* within the passed time interval.
*
* @param {number} duration - The duration of the fade.
* @param {number} [volumeNow=0] - The volume at the start of the fade.
* @param {number} [volumeThen=1] - The volume at the end of the fade.
* @return {Audio} A reference to this instance.
*/
fadeIn( duration, volumeNow = 0, volumeThen = 1 ) {
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@Mugen87 Mugen87 Dec 16, 2025

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I've quickly checked Unreal and they also have fadein/fadeout in their Blueprint API:

https://dev.epicgames.com/documentation/en-us/unreal-engine/BlueprintAPI/Audio/Components/Audio/FadeIn
https://dev.epicgames.com/documentation/en-us/unreal-engine/BlueprintAPI/Audio/Components/Audio/FadeOut

When checking our own methods, I think fadeIn() and fadeOut() should have an optional delay parameter similar to play() and stop(). It's in seconds and you add it currentTime when scheduling the values. New singnature:

fadeIn( duration, volumeNow = 0, volumeThen = 1, delay = 0 ) {

Also, do we need volumeNow? Can't we just use the current volume like in fadeOut(). It seems the Unreal component also just allows to define the target volume.

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@tatsmaki tatsmaki Dec 16, 2025

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Yes I think we can set the volumeNow beforehand

audio.setVolume(0.1);
audio.fadeIn(3, 0.5);

although there might be some issues because setVolume does not set the volume immediately.
it is using the same setTargetAtTime API with a small 0.01 timeConstant.
so it could be setVolume will be canceled by fadeIn

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@Mugen87 Mugen87 Dec 16, 2025 •
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How about we save the value passed to setVolume() is a private variable an use it in the fade methods? In this way, the value set via setVolume() isn't lost when fading in an audio like in https://github.com/mrdoob/three.js/pull/32549/files#r2622754999. The implementation would use:

return this._scheduleFading( duration, this._volume, volumeThen );

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@tatsmaki tatsmaki Dec 16, 2025

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I will check if it works fine or not with the above example
it was just a hypothesis

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@tatsmaki tatsmaki Dec 17, 2025

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I found this old issue #12510

do you remember why setTargetAtTime was used and not setValueAtTime ?

Screenshot 2025-12-17 at 10 22 39
  1. if possible I would replace it with setValueAtTime (instant volume update)
  2. your suggestion with this._volume
  3. this is evil but currentTime + 0.01 * 3 will make sure setVolume smoothing is complete

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@tatsmaki tatsmaki Dec 22, 2025 •
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do we care about cases when people access audio.gain.gain.value directly?
because in this scenario this._volume will not be set

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@Mugen87 Mugen87 Dec 22, 2025

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It's not ideal that gain is public but in general we expect developers work with setVolume().

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@Mugen87 Mugen87 Jan 5, 2026

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audio.setVolume(0.1);
audio.fadeIn(3, 0.5);

I've tested the code today an realized the usage of setTargetAtTime() in setVolume() does not work with the new fading methods. In the above code example, when fadeIn() is executed, the current volume is not set to 0.1 yet which means the interpolation to the target value won't work. After some testing this can only be fixed by using setValueAtTime() in setVolume(). Or by using your original implementation. However, I'm not a fan of setting the current volume in the fade methods since we already have setVolume() for that.

So I think before we can make this change, we have to migrate from setTargetAtTime() to setValueAtTime(). But that requires good testing and some research in older issues since setTargetAtTime() was chosen on purpose, see https://github.com/mrdoob/three.js/pull/32549/files#r2631137839.

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@Mugen87 Mugen87 Jan 5, 2026 •
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After some more reading I'm not feeling comfortable to make the change from setTargetAtTime() to setValueAtTime(). As explained in WebAudio/web-audio-api#76 (comment), setTargetAtTime() provides a De-zippering behavior:

De-zippering is the process of smoothly approaching a target value instead of jumping to it directly. The intention is to prevent audio "glitches" which might occur if the value is changed suddenly.

setValueAtTime() does not:

If a developer explicitly sets values (using setValueAtTime for example) then de-zippering is not performed.

So if we use setValueAtTime(), we risk to introduce (platform specific) audio regressions e.g. when changing the volume. Bugs like crackling sounds were reported in the past (I actually heard them myself) and we don't experience them since we use setTargetAtTime().

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@Mugen87 Mugen87 Jan 6, 2026

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After reconsideration it's probably better to close the PR and let fadein/fadeouts be implemented on application level. _scheduleFading() depends on setValueAtTime() and the consequences of using this method in audio animations are unclear.


return this._scheduleFading( duration, volumeNow, volumeThen );

}

/**
* Fades the audio out by decreasing volume gradually from the current volume to `volumeThen`,
* within the passed time interval.
*
* @param {number} duration - The duration of the fade.
* @param {number} [volumeThen=0] - The volume at the end of the fade.
* @return {Audio} A reference to this instance.
*/
fadeOut( duration, volumeThen = 0 ) {

return this._scheduleFading( duration, this.getVolume(), volumeThen );

}

copy( source, recursive ) {

super.copy( source, recursive );
Expand Down Expand Up @@ -773,6 +802,25 @@ class Audio extends Object3D {

}

_scheduleFading( duration, volumeNow, volumeThen ) {

const currentTime = this.listener.context.currentTime;
/**
* 95% of the duration.
*
* Reference: {@link https://developer.mozilla.org/en-US/docs/Web/API/AudioParam/setTargetAtTime#choosing_a_good_timeconstant}
*/
const timeConstant = duration / 3;

this.gain.gain
.cancelScheduledValues( currentTime )
.setValueAtTime( volumeNow, currentTime )
.setTargetAtTime( volumeThen, currentTime, timeConstant );

return this;

}

}

export { Audio };