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In Reply to: pitch control posted by bobr on February 20, 2002 at 21:26:03:
A *speed* control is the only thing that won't actally cause any type of artifacts other than slowing down or speeding up the audio...I don't think there has ever been an analog device that allows pitch shift. -The Eventide Harmonizer, AMS DMX 15-80, and all the susbequent pitch control devices were all digital. -They work by reading signal into a memory, and reading it back out a fraction of a second later, at a different speed. Let's say you're playing it back faster, to increase the pitch. Sooner or later, the information is going to run out, since you're "emptying the bucket faster than you're filling it" -to strike an analogy. The simple answer is to repeat some sections of the signal, by jumping back in time before the information in the memory buffer runs out.
These 'jumps' are known as 'glitches', and some manufacturers (AMS were a good example) developed algorythms that made the 'jumps' at same-direction zero-crossing points to make the transistions less audible. (the "de-Glitch" card on the DMX-15-80S)
Likewise, when shifting pitch down, the information is read out slower than it is added, so to prevent "bucket overflow", some information is discarded, and never played back.
Voila. -That's how a standard harmonizer works. -There's no real analog analogy, although I did work on a design that used three CCD devices, cross-fading between them, and "flushing" the muted device... whilst not digital, it sounded significantly worse, (noisier... well it's a bucket-brigade device) and was limited to significantly sub-octave shift range.
Nowadays, glitch-free near real-time, formant-preserving (i.e. humans stil sound like humans at a different pitch... not monsters or chipmunks... -it's really spookily good... a man can sound like a woman, or bice-versa!) pitch processing is available in software, employing spectrally-based processing.
Go digital. Long live analog, (It's my life, I tell ya!) -but this is one job that really needs to be done by a computer!
Keith
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Follow Ups
- Re: pitch control - SSL Tech 06:55:20 02/21/02 (0)
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