[sdiy] A different approach to frequency shifting?

[Czech Martin]

I remember that this one was an exercise in my communication theory
courses on university. Just a feeling: suspiciously simple, too simple.
I did not do the math yet.
I mean the task to get rid of one sideband is not at all simple.
This article suggests  that it would be simple (no special requirement
for the LP filters).
Smells like nonsense, but I could be wrong.

For analog implementations the scheme suffers from that
the input is not necessarily band limited, i.e. the folded
sideband can possibly creap up into the other sideband
area. This can of course be excluded in a sampling system.

m.c.

-----Original Message-----
From: Thomas Hudson [mailto:thomas_hudson at mac.com]
Sent: Donnerstag, 24. April 2003 21:29
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] A different approach to frequency shifting?



I came across an article in CSound Magazine from Summer 2000 about an approach to frequency shifting I hadn't seen before. It uses a quadrature oscillator and two multipliers followed by two LP filters and then another quadrature oscillator and pair of multipliers. The difference in frequency between the two oscillators determines the shift:

http://www.csounds.com/ezine/summer2000/processing/index.html

It seems that this method would be simplest for thru-zero effects. The article is in the context of a digital implementation, but has anyone used this technique in the analog world?

TH