Re: How can I subtract one frequency from another ???

On Sun, 08 Jan 2006 23:28:46 GMT, "Frank" <technician@xxxxxxx> wrote:

>
>A bit more info on the application, the input will be either sound such as
>music, (well within the human hearing range) or pure tones (sine waves).
>I will be squaring up the output with an LM339 comparitor to drive a logic
>level input IGBT.
>If the 565 needs a square in, I could figure something out, but would rather
>have the input to the comparitor reasonably "preserved".

Please explain what your ultimate goal is here... I sense impending
doom! In general, if you multiply (a better term than "mix" at audio
frequencies, where "mix" almost always means "linear sum") one sine
wave by another you will get only sum and difference frequencies in
the output. If you are interested in only the difference frequency,
you would need to filter out the sum frequency. This is a non-trivial
problem for the frequency ranges you mention.

But on top of that, you mention that one input will be a sound
such as music. But music is (typically!) composed of many
different frequencies sounding at the same time (multiple
instruments, chords, harmonics, etc). So there is no hope of
getting a single difference frequency (difference with what?).

Perhaps with more details we can suggest a workable
solution, or at least save you a disheartening failure!

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

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