Re: DynamicsCompressor and emphasizing high frequencies

Thanks, that's good background.  It seems from this, though, that
either 1) users should do this themselves, or 2) we should provide a
control parameter on the emphasis, possibly multiple controls (after
all, the "default" on the LA2A is no emphasis).  My inclination is to
remove the emphasis, but that will require changing all current
implementations.  Alternately, we need to carefully specify what
emphasis is being applied, so it can be undone (by
pre-pre-de-emphasizing, and post-post-emphasizing, which seems a
bit...odd.)

This is causing problems in multiband compression (which we use in
Chrome OS for speaker tuning), as well as other side effects.

Any comments on removing this emphasis?

From: <gaito@g200kg.com>
Date: Fri, 10 Jan 2014 05:54:26 +0900
To: Chris Wilson <cwilso@google.com>
Cc: public-audio@w3.org
Message-Id: <20140110055426.5059.8BE7BE0E@g200kg.com>

Some kind of compressor has emphasis control knob.
For example, famous vintage compressor 'LA2A' has that.
This function is originaly designed for FM broadcast application
to avoid over modulation. But now, may be used to fine adjustment
of favorite sound colors.
(WebAudioAPI's gain curve seems be same as FM broadcasting
emphasis curve)

IMO, emphasis is not essential to standard compressors
It is a category of know-how of paticular equipments.
http://www.uaudio.com/media/assetlibrary/l/a/la-2a_manual.pdfhttp://www.uaudio.com/blog/la-2a-collection-tips-tricks/

----------------
Tatsuya Shinyagaitogaito@g200kg.com
<gaito@g200kg.com?Subject=Re%3A%20DynamicsCompressor%20and%20emphasizing%20high%20frequencies&In-Reply-To=%3C20140110055426.5059.8BE7BE0E%40g200kg.com%3E&References=%3C20140110055426.5059.8BE7BE0E%40g200kg.com%3E>




On Thu, Jan 9, 2014 at 1:50 PM, Karl Tomlinson <karlt+public-audio@karlt.net
> wrote:

> Chris Wilson writes:
>
> > 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).  [...]  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.
>
> I assume the intention is to make the *perceived* level of the
> signal more constant.
>
> It seems reasonably effective to my ears, but I haven't compared
> other techniques.
>