[vorbis] Lowpass filter option required

[Ross Levis]

Unfortunately the LAME filters are implemented on the output of the MP3
filterbank, which of course is not used by Vorbis.

Monty said at the time that it would be a simple matter to add filter options.
The first release of the OGG encoder had a hardcoded lowpass filter of around
17.5khz I think it was, so here must be code there already?

Ross.

Michael Smith wrote:

> At 05:39 PM 11/15/00 +1300, you wrote:
> >I mentioned many months back that I intend to switch to Ogg/Vorbis from
> >MP3/LAME once the final version is out but I need to have an adjustable
> >lowpass filter option similar to LAME's.  If this isn't done yet, could you
> >please add it to your list for OggEnc.  Specifically I need to cut all
> >frequencies above 17khz.
>
> I suppose this would be useful for some people - but it's not exactly high
> on our list of priorities. I suggest that you pipe your audio through an
> external program (sox can presumably do this), then through oggenc.
>
> In the future, similar functionality might go in (much faster if someone
> decides to write some filter code for oggenc...), but for the immediate
> future, I don't think it's likely to be added (it doesn't belong in
> libvorbis itself, as far as I can see, and I don't really have time to add
> it to oggenc myself)
>
> It's also possible that LAME's vorbis code will use the LAME filter code
> before passing data to libvorbis, if you specify appropriate options - the
> lame code needs some minor updates for current libvorbis, but those should
> be very simple.
>
> Michael
>
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