Re: Lower WAV pitch problem
- Posted by 1evan at sbcglobal.net
Jun 03, 2003
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>
>
>
--
|\ _,,,---,,_
/,`.-'`' -. ;-;;,_
|,4- ) )-,_..;\ ( `'-'
'---''(_/--' `-'\_)`-'\_)
|
Not Categorized, Please Help
|
|
