[sdiy] frequency shifter

[Eric Brombaugh]

On 3/14/20 5:26 AM, ColinMuirDorward wrote:

> Has anyone seen this implemented in a digital FX unit?
> Here <https://www.fullbucket.de/music/freqshifter.html>is a vst I'm 
> looking forward to trying out.

There are lots of digital implementations of frequency shifters out 
there - the quadrature oscillator / multiplier is a fundamental 
operation of most digital radios and the dome filter (aka Hilbert 
Transform, aka analytic signal converter) is straightforward to 
construct with allpass networks.

There are a few sites out there that discuss this. I think the oldest 
one I know of is from C Sound:

http://csoundjournal.com/ezine/summer2000/processing/index.html

Olli Niemitallo gave a good backgrounder on construction of a Hilbert 
Transform filter:

http://yehar.com/blog/?p=368

I've implemented the Hilbert approach in several synth modules:

http://www.modcan.com/emodules/dualfreqshifter.html

https://synthtech.com/eurorack/E560/

The algorithm is simple enough to run in a low-end ARM processor.

Eric