[sdiy] A different approach to frequency shifting?

[Czech Martin]

I think that the LP filter must have a very sharp cut off,
brick wall, so to say.
In digital domain this is not too difficult, but time
consuming. 
The question is if oversampling, high frequency mixing,
bandpass, downmixing and downsampling won't do the trick.

Analog get's very diffcult.
So this approach offers only one advantage over the higher
frequency operation devices: it uses folding of the lower
sideband in order to get modulator frequency down, thus
reducing the requirements for pass band -stop band transfer
to some degree.

m.c.

-----Original Message-----
From: Martin Fay [mailto:martin at manikin.force9.co.uk]
Sent: Freitag, 25. April 2003 12:38
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] A different approach to frequency shifting?


>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.

>From a brief reading of the article it looks like like the filter
actually needs to be an effective halfband/anti-aliasing filter.
Definately not "no special requirement" in my book.


Martin

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