Re: Lower WAV pitch problem
(looking very stupid) when I suggested just tacking copy of wave onto end
of wave to double duration without pitch shift, I was just considering my
simple wave, not the general & more realistic case, sigh. <head hits
keyboard: tyughjvbn>
Does fourier analysis yield a set of sine waves which when re-combined yield
the original waveform?
How do you do fourier analysis? :))
How do you discern noise, just high frequency?
I'm interested in changing human voice samples by lowering pitch, but
thinking to only lower vowel portions of the sample, not sibilance &
explosives (or whatever they're called, like "PoP", "Boom", "Take", etc), so
I'd need to be able to discern them. I'm getting the impression it's more
like juggling chainsaws than knives :)
Dan Moyer
----- Original Message -----
From: "David Cuny" <dcuny at LANSET.COM>
To: "EUforum" <EUforum at topica.com>
Sent: Tuesday, June 03, 2003 12:18 AM
Subject: Re: Lower WAV pitch problem
>
>
> Daryl Van Den Brink wrote:
>
> > I don't know what you could be doing to double the duration
> > and make it's pitch stay the same, but I'd love to find out.
>
> This turns out to be solvable, but non-trivial. Sound basically decomposes
> into two types: sound carrying harmonic content, and noise.
>
> First, you chop up the sound into sufficiently small chunks. If you make
the
> chunks to small, you don't capture enough harmonic information. If you
make
> them too large, you end up getting "pre echo" because you're including
> information that doesn't belong in that timeframe.
>
> To derive the harmonic content, you do a fourier analysis on each chunk.
>
> To derive noise content, once you decide that a chunk contains noise, you
do
> bark banding on it. Noise doesn't have to be pitch shifted in the
> reconstruction.
>
> You also need to look at the volume, so you can build a volume envelope
when
> you rebuild the sound.
>
> Now you've got enough information to reconstruct the sound. Take the
chunks
> that have harmonic content, and rebuild their harmonics to the new pitch -
> just reverse the fourier process. The noise chunks are rebuilt out of the
> bark bands. Join all the chunks together and recreate the volume envelope
to
> match the original sound.
>
> Easy, huh?
>
> Sorry, I don't have the references available. That's the point I threw up
my
> hands and decided to try something easier, like herding cats or juggling
> knives...
>
> -- David Cuny
>
>
>
> TOPICA - Start your own email discussion group. FREE!
>
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