Re: Lower WAV pitch problem
Jeeze!!!! It's even got stuff about neural nets! Thanks, I'll see if I can
understand any of it :)
Dan Moyer
----- Original Message -----
From: <1evan at sbcglobal.net>
To: "EUforum" <EUforum at topica.com>
Subject: Re: Lower WAV pitch problem
>
>
> Check out www.dspguide.com.
>
> Dan Moyer wrote:
>
> >
> >(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
> <snip>
>
> >
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