[vorbis] Few questions concerning clipping

[Beni Cherniavsky]

On Sun, 25 Feb 2001, Aleksandar Dovnikovic wrote:

> I noticed that clipping occurs in lossy audio compression even
> if there is no clipping in the original file (though the original
> file has peaks that are just below the maximum). I know
> that this happens due to all the filtering involved during compression,
> but I'm wondering just how audible this clipping is because I don't
> hear anything wrong.

Do you have some numerical observertions?  I'd be interested to know.  It
is expectable that this can occur, so I always try to limit (by scaling
the volume to the minimum of 98%-max-sample and 0.15-RMS which I have on
most my songs) my input files to 98% of the maximum assuming that this is
enough - but I never checked that it really is.

It is possible that the decoder can change the volume during decoding
before clipping can occur, thus avoiding it if the volume is below
maximum.  Winamp's mp3 input plugin can do fast EQ which I assume is done
before the conversion to pcm domain.  Vorbis can't do it now afaik - maybe
it'd be useful to add a volume scaling parameter to the decoder (encoder
too?) that will allow one to decode a vorbis files that represents >100%
samples without clipping.

> [snipped]


-- 
Beni Cherniavsky <cben at crosswinds.net>
                 (also scben at t2,cben at tx in Technion)

  (/bin/ch x)^2 = (/bin/sh x)^2 + 1

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.