Bug 95792 – WebAudio: limit output level to 0db

• Component: New Bugs
• Status: RESOLVED FIXED

[Jer Noble]

WebAudio: limit output level to 0db

[Jer Noble]

<rdar://problem/11966135>

[Jer Noble]

Created attachment 162124 [details]
Patch

[Jer Noble]

Created attachment 162125 [details]
Patch

Set frequency of test to within the average human hearing range.

[Alexey Proskuryakov]

Comment on attachment 162125 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=162125&action=review

> Source/WebCore/ChangeLog:4
> +        WebAudio: limit output level to 0db
> +        https://bugs.webkit.org/show_bug.cgi?id=95792

Could you please add Radar link here, too? It's always a good idea to have these readily accessible.

[Jer Noble]

Created attachment 162273 [details]
Patch

Sure thing.  Also added a couple of missing ASSERTS to AudioDestinationMac::configure()

[Chris Rogers]

Hi Jer, I highly recommend against using AUPeakLimiter in this case.  It's more of a mastering effect and will "touch" the audio signal in ways that would be undesirable.  It also has a processing latency.

Instead, I recommend looking at AudioDestinationMac::render() after this call:

    m_callback.render(0, &m_renderBus, numberOfFrames);

I would simply go through each AudioChannel of m_renderBus and "clamp" all the PCM data to be within the range -1 -> +1

[Jer Noble]

Created attachment 168771 [details]
Patch

[Chris Rogers]

Comment on attachment 168771 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=168771&action=review

Looks fine to me with some small nits.

> Source/WebCore/ChangeLog:12
> +        >0db buffers and effects.

I'd update the ChangeLog comment here

> Source/WebCore/platform/audio/VectorMath.cpp:115
> +void vclip(const float * sourceP, int sourceStride, const float* lowThresholdP, const float* highThresholdP, float* destP, int destStride, size_t framesToProcess)

style nit: "float *" -> "float*"

> Source/WebCore/platform/audio/VectorMath.cpp:651
> +void vclip(const float * sourceP, int sourceStride, const float* lowThresholdP, const float* highThresholdP, float* destP, int destStride, size_t framesToProcess)

style nit: "float *" -> "float*"

> Source/WebCore/platform/audio/VectorMath.h:53
> +void vclip(const float * sourceP, int sourceStride, const float* lowThresholdP, const float* highThresholdP, float* destP, int destStride, size_t framesToProcess);

style nit: "float *" -> "float*"

> ManualTests/webaudio/limit-level-0db.html:36
> +    </p>

Maybe update comment - Strictly speaking, you'll hear the "clipping", thus the sine wave will be clipped into the form of a square wave, but it shouldn't get radically louder than the full-scale sine wave

[Jer Noble]

Committed r131459: <http://trac.webkit.org/changeset/131459>