[gstreamer-bugs] [Bug 340362] [PATCH] new plugin - hardlimiter

[GStreamer (bugzilla.gnome.org)]

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GStreamer | gst-plugins-bad | Ver: HEAD CVS


René Stadler changed:

           What    |Removed                     |Added
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                 CC|                            |mail at renestadler.de




------- Comment #10 from René Stadler  2006-09-21 18:21 UTC -------
I have to say that this element is _not_ a hard limiter.  Also, it is _wrong_
to say that hard limiting sounds bad and it _is_ true that this element just
does clipping (which can never sound better than "sound card clipping").  Using
this element can only mess up the output, I don't see a use case for it.  The
example about consumer DACs that the reporter provides is flawed.

-6 dB hard limiting means to apply a transfer function like

   ouput = tanh ((input - 0.5) / 0.5) * 0.5 + 0.5

to all values with input > 0.5 and a respective negative variant for values < 
-0.5.

This will smoothly compress values above 0.5 (ca. -6 dB), which has the
following advantages:

  - You can input values >1.0 and still get a good sounding output (unless you
really overdo it).  This is of use for ReplayGain if you disable clipping
prevention (which you don't have to).

  - The dynamic range gets reduced (input 1.0 -> output  ca. 0.88).  This
allows you for example to listen to classical music through loudspeakers in
front of a computer (noisy environment), or for playing music on a party.  This
is entirely unrelated to ReplayGain.

You really have to watch out when investigating about DSP stuff on the web. 
Lots of seemingly useful documents talk about an analog processing background. 
I assume this is how the reporter got the wrong idea that clipping is useful. 
In the analog world, you need such a thing as protection for equipment or as
last resort protection to make sure output is always within certain limits
(radio stations).


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