[vorbis-dev] Pitch Control

[Beni Cherniavksy]

On 2002-02-13, ...oO--Kerry--Oo... wrote:

> Hello there folks,
>
> i was having a look through bits of the code to see if there was anything to do
> with pitch control, or perhaps i should call it speed control.
>
> For instance, say you took a track off a DVD which is 48khz, forgot to run it
> through sox to downsample it to 44khz, yet encoded it anyway.  It will sound
> slower (therefore, the pitch has dropped).
>
> Whilst dj-ing (though i am no dj-god), blending the beats can be a bit tricky
> without being able to control the speed and bend the timing a little.  I have
> seen a few utilities for mp3 files somwehere which allow one to do this
> realtime (or as realtime as it gets).  There are also many decks which allow a
> CD's pitch to be moved around to.
>
> The current setup is a bit lame ;) with two soundcards playing the tunes into
> an external mixer, along with LP players, and a lot of start-stop button action
> goes on to get the little beat LED's in sync...
>
> Any ideas?
>
Speed control when playing distors the pitch so the psychoacoustics
assumptions when encoding are not valid.  So if you "bend" the time
noticably you might experience artifacts.  Maybe higher -q's will save you
or maybe special changes would be necessary (something like applying a
max-of-a-window (or min as appropriate) filter to all psycho-acoustic
curves, to make yourself safe for pitch distortions up to X Hz, and
allowing one to specify X on the command line...)  But I don't know
anything about the psycho-acoustic details of Vorbis so I can't say more.


-- 
Beni Cherniavsky <cben at tx.technion.ac.il>
                 (also scben at t2 in Technion)

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