[sdiy] Frequency shifters, again

[jhaible]

> I forgot to speak up before when you first mentioned this topic...
>
> I've seen this before.  (!!!)  It was an old issue of the Journal of
> the Audio Engineering Society, roughly around 1974.
>
> It was a voltage controlled filter built with two balanced modulators,
> a fixed filter between them, and a VCO.  At least two pages long, with
> a block diagram.
>
> Unfortunately that's all my feeble memory can provide.  It probably
> wouldn't be difficult to hunt this down at a university library.


The setup should be straight-forward:

Dome filter, two modulators, adder, fixed filter, dome filter, two
modulators,
subtractor. Both pairs of modulators modulated by the same quadrature
oscillator.

JH.