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From: email@example.com (Gibbo)
Date: 19 Jan 2003 21:07:25 GMT
Organization: AOL, http://www.aol.co.uk
Subject: Re: Wombat's Revenge
John Larkin wrote:
>Would some kind soul please explain to me
>What's the difference between a frequency shifter and a pitch shifter?
>What are they used for?
>How do they generally work?
>Any other fun facts.
A pitch shifter moves *everything* up or down by a percentage of it's
frequency. As the pitch of a note is related to the log of the frequency, so
shifting all frequencies by a certain percentage of itself retains the harmonic
relationship between all the notes. eg middle A=440Hz, A an octave higher =
Move them both up by say 10% and they become 484Hz and 968Hz. Still an octave
apart. This is a pitch shifter. They are used for adding a fixed musical
interval to an instrument for effect reasons, to change the pitch of an entire
piece of music (or the singer's own voice) etc.
Pitch shifters (usually) work by A/Ding the incoming signal, storing in a dual
port RAM then reading the data out at a different rate then D/Aing. You will
immediately see a flaw in this in that if the data is read out faster than it
is written in, then it will run out of data. Some tricks are used to re read
certain sections (on a cycle by cycle basis) to fill in the gaps. The first
units of this type did suffer some quite severe glitching at certain pitch
changes but the new algorithms are *so* good that it is all but impossible to
tell the difference. All the ear hears is a change in pitch with no other
artifacts. Most recent comercial recording have made use of pitch shifters
somewhere in the chain.
As an aside some of the more clever ones can alter the pitch change depending
upon the note being played and therefore give a true harmony (which isn't a
fixed interval throughout a scale).
A frequency shifter adds say 10Hz to all frequencies. So in the example given
above the new notes would be 450Hz and 890Hz which now have a completely
different harmonic relationship to each other.
Pitch shifters are musical. Frequency shifters (despite some [non-musicans]
assertions to the contrary) are far from musical.
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