[sdiy] [synth-diy] lock-in amplifiers

[rburnett at richieburnett.co.uk]

> Thanks. I've long thought about a design of filters where parts run at
> different frequencies, but haven't heard of multirate filters yet.
> It'll be interesting reading for sure!

It helps for certain types of filters that would otherwise demand 
hundreds or thousands of filter taps.  That document does a very good 
job of explaining it in clear english.  Just add the string to your bow 
and use when appropriate.

-Richie,