Inconuucl wrote:Pitch is frequency. A pitch shift is just a quantized frequency shift.
Well that may be, but the way a pitch-shifting delay and frequency-shifting change the note
seems to be different. At least that is what I gathered from this post that Sean Costello (valhalladsp)
wrote on a tgp thread about the Bicycle Delay:
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"Frequency shifter" refers to something very different than pitch shifting. A frequency shifter adds a constant offset to every frequency present in the signal, while a pitch shifter (ideally) multiplies every frequency by a factor.
For example, imagine that you are playing the A string on your guitar. Your signal will have the following frequencies in it:
110 Hz (the fundamental)
220 Hz (2nd harmonic, 2X the fundamental)
330 Hz (3rd harmonic, 3X the fundamental)
440 Hz (4th harmonic, 4X the fundamental)
550 Hz (5th harmonic, 5X the fundamental)
etc.
If you ran your guitar through a pitch shifter, shifting up by +7 semitones, you'd have the following harmonics in the output:
165 Hz (the new fundamental)
330 Hz (the new 2nd harmonic, 2X the new fundamental)
495 Hz (the new 3rd harmonic, 3X the new fundamental)
660 Hz (the new 4th harmonic, 4X the new fundamental)
825 Hz (the new 5th harmonic, 5X the new fundamental )
with all the remaining harmonic frequencies being 3/2 times the original frequency.
The pitch shifter will preserve the harmonic ratios of the frequencies in your signal...ideally. In reality, there are often some weird sidebands generated by the pitch shifting process, but we can ignore that for now.
A frequency shifter will add a constant offset to the frequencies. Let's say that you shift up by 55 Hz, so that the base frequency of the note matches the output of the pitch shifter set to +7 semitones. The output would be:
165 Hz (the new fundamental)
275 Hz (the new 2nd "harmonic," 1.6667 times the new fundamental)
385 Hz (the new 3rd "harmonic," 2.3333 times the new fundamental)
495 Hz (the new 4th "harmonic," 3 times the new fundamental)
605 Hz (the new 5th "harmonic," 3.6667 times the new fundamental)
The output of the frequency shifter is no longer a signal with harmonics spaced at integral multiples of the base frequency. The new overtones are at weird, non-integer ratios. The sound of this is very clangorous, and is closer to a bell than a guitar string. Play a note besides A, and things will sound even weirder.
The concept of putting a frequency shifter in the feedback loop of a delay dates back to Delia Derbyshire's work on Dr. Who:
https://valhalladsp.com/2009/05/19/the- ... nd-dr-who/
It's a cool sound, and very different than putting a pitch shifter in the feedback loop of a delay.
Sean Costello
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