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Pitch vs. Frequency (again)

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Pitch vs. Frequency (again)

Postby shurikt » Fri Aug 30, 2019 7:43 pm

I was reading the review of the Valhalla Delay in the July issue (yes, I read slowly - but on the bright side I never run out of SOS articles!) and got to this sentence, which broke my brain a little:

"Finally, there's Ghost, an intriguing algorithm that employs frequency-shifting rather than pitch-shifting to achieve interesting and sometimes clangorous effects."

Going with my personal definitions of the relationship between pitch & frequncy, i.e., pitch is the human perception of a set of frequencies of particular amplitudes, what does this sentence even mean?

Is this pitch-shifting algorithm, then, modifying the fundamental, whereas the frequency-shifting one is modifying the harmonics? Isn't *everything* frequency-shifting?
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Re: Pitch vs. Frequency (again)

Postby Hugh Robjohns » Fri Aug 30, 2019 9:01 pm

Pitch Shifting normally refers to the alteration of a signal's frequency (and harmonics) by established musical intervals -- and so it is measured in cents or semitones etc. It's what happens when you speed up or slow down a DAW or audio recorder etc. All the notes and octaves maintain their musical relationships. Mathematically, it's a multiplication process - each input frequency is multiplied by a set amount, hence musical intervals are preserved.

Frequency Shifting also changes the frequency of a signal, but in a very different way. Its a specific form of frequency modulation, technically, which results in each separate frequency component being moved up or down by a set number of Hertz. In other words, its an additive process. It's also a very different (and decidedly unmusical, or at least an unfamiliar) effect, and quite unusual to find.

I've only ever come across it in a practical sense in a PA howl-round suppression system from the 80s that shifted everything by 5-10Hz. Remarkably effective, and strangely unnoticeable on speech at low shift amounts... But a bit odd-sounding if feedback is provoked, and on musical sources.

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Re: Pitch vs. Frequency (again)

Postby shurikt » Sat Aug 31, 2019 4:57 am

Interesting! Thanks!
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Re: Pitch vs. Frequency (again)

Postby awjoe » Sat Aug 31, 2019 6:09 am

Hugh Robjohns wrote: Its a specific form of frequency modulation, technically, which results in each separate frequency component being moved up or down by a set number of Hertz. It's a very different (and decidedly unmusical) effect, and quite unusual to find.

If it's that rare, why would the person who reviewed the Valhalla delay have referenced it, then?

And why would Valhalla have used it in their plugin?

I guess it's a 'you have to listen to the plugin' thing to understand it.
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Re: Pitch vs. Frequency (again)

Postby Kwackman » Sat Aug 31, 2019 10:50 am

awjoe wrote:If it's that rare, why would the person who reviewed the Valhalla delay have referenced it, then?
Because it's rare and unusual!

awjoe wrote:And why would Valhalla have used it in their plugin?
To try to give their plug-in a USP in a very well stocked market.
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Re: Pitch vs. Frequency (again)

Postby Elephone » Sun Sep 01, 2019 6:08 pm

I presume it doesn't necessarily shift the perceived pitch of the delays (from that of the source), but rather alters the frequency content, the harmonic composition of the delays over time (from that of the source).
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Re: Pitch vs. Frequency (again)

Postby Wonks » Sun Sep 01, 2019 8:33 pm

I would have thought it will alter the pitch of the repeat, and alter it again for the next repeat. It's going to sound weird, but that's the intent. Plenty of normal sounding delays out there, plus if you wants some weird sci-fi effects, then this mode should do well.
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Re: Pitch vs. Frequency (again)

Postby Hugh Robjohns » Sun Sep 01, 2019 10:18 pm

I found the Wireless World description of the frequency shifting howl round suppressor on Keith Snook's website here:

http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1973/Frequency%20Shifter%20For%20Howl%20Suppression.pdf

Although much of the article concerns the actual circuit design, it also describes the background concept and how it works, as well as its practical application and audible effects. It also mentions Bob Moog's development of a similar device for electronic music applications: the 1630 Bode frequency shifter. https://moogfoundation.org/wp-content/uploads/1974-Bode-Frequency-Shifter.pdf

And if you'd like to play with the effect, I found a donation-ware version here:

https://www.fullbucket.de/music/freqshifter.html
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Re: Pitch vs. Frequency (again)

Postby shurikt » Wed Sep 25, 2019 8:09 am

The description of the VST that Hugh posted just above answers beautifully:

Do not confuse the Frequency Shifter with a pitch shifter! A pitch shifter multiplies all frequencies of the input signal by a constant factor while a frequency shifter adds (or subtracts) a constant amount of Hertz to (or from) those frequencies. Thus, the harmonic structure of the input signal will not be preserved in the modulated signal, resulting in a raw, inharmonic, metallic, you-name-it sound the more you apply the effect. Even more, if you mix a slightly shifted signal with the original input signal you will get some uncommon phasing sound.
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