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'[OT]:Mathematics of pitch shifting'
2001\03\22@114356 by

Here's a question for those familiar with DSP.  Any help would be
appreciated.

I'm working on a project to shift the pitch of a complex waveform in
real time.  The pitch shift will always be upward -- that is, the
frequency of the output will always be higher than the original.
The size of the shift in Hz needs to be determined by a local
frequency source and may change rapidly.  From ham radio days, I
remember that this is similar to generating single sideband signals.
A local oscillator is mixed with the waveform to generate sum and
difference frequencies.  The signal could be shifted 10 Hz , by
mixing it with a 10 Hz sine wave and filtering out the lower
sideband.  What I would like to do is eliminate the need for
filtering out one sideband.

If both signals are digitized, multiplying the two together and
normalizing the result will produce the two sidebands (both sum and
difference frequencies).  Unfortunately, this is where my math fails
me.  Years ago one of the Radio Amateur's Handbooks published a
formula for generating a single sideband using fairly simple math
and trig functions, but that Handbook is long gone.  Does anyone
know what the formula is or where I might find it?  I suspect that
this is a common problem in DSP work, but I am a real novice in that
black art.

Thanks,
Michael

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You can do this by building an image reject mixer. The description is rather
lengthy, but an excellent article by Rick Campbell, "High Performance
Single-Signal Direct Conversion Receiver", was published in the Jan 1993
issue of QST. Contact http://www.arrl.com I believe they can provide you with a
copy of the article. This type of mixer does exactly what you have described

Hope this helps. If you need more detail. You can contact me at
kizeriansarcos.com or kizerianqwest.net on weekends.

Bruce Kizerian
{Original Message removed}

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