[sdiy] frequency shifter

ColinMuirDorward colindorward at gmail.com
Sat Mar 14 16:28:07 CET 2020


Yes, I was wondering about digital HW version because the job seemed well
suited to that domain.
If I was more digitally inclined, I might try to set one up on that new
Daisy board, or an Axoloti.
C


On Sat, Mar 14, 2020 at 2:03 PM Richie Burnett <rburnett at richieburnett.co.uk>
wrote:

> If you want good performance, the tolerances on the phase shift networks
> are quite stringent. So it's actually easier to make a decent frequency
> shifter using digital filters than it is using analogue filters. With IIR
> digital filters you can get the poles exactly where you want them and they
> won't drift with age or changes in ambient temperature.
>
> Functions like multiplication are also usually mathematically perfect to
> the precision of the ALU when preformed digitally, but are often an
> approximation with unwanted distortion, noise and feed-through when
> implemented with analogue electronics.
>
> Likewise, even simple addition and subtraction of signals are limited by
> the tolerance of resistors in analogue mixing circuits, or have to be
> manually trimmed. In the digital domain, if you add together two numbers
> you get a precisely even weight of the two values, without any tolerance,
> trimming or temperature drift issues.
>
> -Richie,
>
> Sent from my Xperia SP on O2
>
> ---- Eric Brombaugh wrote ----
>
> >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
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