[sdiy] [synth-diy] Frequency shifter which rejects negative frequencies

cheater00 . cheater00 at gmail.com
Sun Jan 26 18:27:51 CET 2014


On Sun, Jan 26, 2014 at 6:21 PM, Donald Tillman <don at till.com> wrote:
> your description is confusing, but I think you're describing a tunable heterodyne filter.  Basically, given an audio input and a carrier frequency:
>
>     multiply audio input by carrier frequency ->
>     through a fixed filter ->
>     multiply again by carrier frequency

Not too sure of the specifics myself. The articles I linked to expound
in great detail - and can likely be better understood by minds greater
than mine :-)

What I understood is that the fixed filter is pretty much set to DC,
and multiplying by the carrier frequency makes the carrier frequency
from the audio input fall on 0Hz after mixing, therefore within the
pass band of the filter.

There's no multiplying after that - the low-pass filter already
recovered the amplitude modulator.

Cheers,
D.



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