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DynamicsCompressor and emphasizing high frequencies

From: Chris Wilson <cwilso@google.com>
Date: Thu, 9 Jan 2014 11:34:34 -0800
Message-ID: <CAJK2wqVzwC3wfKB_kB_VUTGh2y428qx0nO6nJsGQmSvXuXrLUA@mail.gmail.com>
To: "public-audio@w3.org" <public-audio@w3.org>
Does anyone have any experience with the pre- and post-emphasis in the
DynamicCompressor?  I notice that the Webkit/Blink code has a
pre-compression boost to high frequencies (details referenced in the
original Webkit bug: https://bugs.webkit.org/show_bug.cgi?id=60682#c2, but
not explained).  I can't find any obvious reference to why you would
pre-emphasize high frequencies like this; it's not commonly described.  It
has the effect of increasing compression due to higher frequency components
- for example, you can open up
http://webaudiodemos.appspot.com/compressorfreq/, which has a sine wave
oscillator feeding into a DynamicsCompressor; just increasing the frequency
of the oscillator ends up attenuating the signal.  You'd expect the level
of the signal to remain constant, regardless of frequency. (Note this does
not attenuate higher frequencies differently - there is a post-compression
de-emphasis as well - it just causes them to affect compression more.)

I notice that Firefox appears to have the same pre/post emphasis.

Thoughts?  At the very least, obviously, this needs to get captured in the
spec.

-Chris
Received on Thursday, 9 January 2014 19:35:05 UTC

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