[sdiy] frequency shifter

Gordonjcp gordonjcp at gjcp.net
Thu Mar 12 23:09:25 CET 2020


On Tue, Mar 10, 2020 at 10:51:12PM -0400, ColinMuirDorward wrote:
> Also, can you explain like I'm stupid the difference between pitch and
> frequency shifting? It sounds like a linear vs exponential thing, but must
> be more to it than that...

It is indeed a linear versus expo thing.  Pitch shifting is what you get when you speed tape up - double the speed, double the pitch.  An octave jump is still an octave, it's just both are an octave higher than before.  You multiply the frequency.

Frequency shifting adds to the frequency, instead of multiplying.  So a low A on a guitar string at 110Hz shifted up 110Hz would be 220Hz, an octave up.  But, if you fed in 220Hz you'd get 330Hz out, an E instead of an A, and 330Hz in would give you 440Hz, an A, and 440Hz in would give 550Hz or a slightly flat C#, and 550Hz would give you an E again, and so on.

You can imagine how mangled that would make things sound.

Or actually, you don't need to:

https://minecraft.gjcp.net/9970kHz.ogg

This is an AM shortwave radio station being tuned in and out on an SSB receiver, which is really just a big Bode frequency shifter.

-- 
Gordonjcp



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