[vorbis] Lowpass filter option required

[Ross Levis]

A lowpass filter will be required for low bitrates so I presume it will get in
there eventually.  I'm currently using Windows not Linux so can't use sox.  Unless
I can find a stdin/out DOS filter somewhere, unlikely.

Cheers,
Ross.

Michael Smith wrote:

> At 08:29 PM 11/15/00 +1300, you wrote:
> >Unfortunately the LAME filters are implemented on the output of the MP3
> >filterbank, which of course is not used by Vorbis.
>
> Ah. I wasn't sure if that was the case. Oh well.
>
> >
> >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?
>
> I think that 'lowpass filter' was in the psychacoustic code (though at the
> time I didn't understand the code as well as I do now, so I could be
> misremembering. Monty could presumably give a more definitive answer). It
> had more or less the effect that you want, but doing this as a general
> means of lowpass filtering is not the best idea, from a quality perspective.
>
> There is also some general filter code present in vorbis (used for other
> purposes) which could probably be adapted easily for lowpass filtering.
> However, it's still not completely trivial to do it decently, and it's of
> little use to most people. Additionally, since you can just go through some
> external program (sox?), there's little incentive to give this high
> priority. I'm not sure what you think is wrong with doing this...
>
> I guess it's something that should go in there, but there are lots of other
> things with much higher priority for Monty, and other people don't really
> have the time (like myself. Damn exams).
>
> Michael
>
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