[sdiy] Digital accumulator VCO core?

Brian Willoughby brianw at audiobanshee.com
Mon Feb 15 23:06:17 CET 2021


Are you saying that you've never run into CPU overload in your DAW? There's a lot of unnecessary code in autotune that isn't needed for spectral gate.

My musician friends are always finding the limits of their CPU when composing, and have to freeze tracks to continue. Being a little conservative on code design can go a long ways to make things easier for the composers out there.

There are plenty of FFT based effects available in source code that you could use as a basis. Autotune isn't the only starting point.

Brian


On Feb 15, 2021, at 14:00, Mike Bryant wrote:
> My point was that once you've done the autotune algorithm, adding gating by bucket is simple.  Everyone has the source-code for an autotune algorithm or two on their DAW nowadays so why bother to create something simpler ?
> 
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Brian Willoughby
> Sent: 15 February 2021 21:22
> To: SYNTH DIY
> Subject: Re: [sdiy] Digital accumulator VCO core?
> 
> I think you're conflating autotune and spectral gate. They do both have FFT in common, but so many effects have FFT in common and that doesn't mean they're necessarily related.
> 
> My point is that the spectral gate does not need to make any attempt to work out the prime element in each band, and that's a very expensive algorithm. If you're not dealing with the most expensive calculation in one effect (autotune) then there's no real need to consider it the same as or even related to another effect (spectral gate).
> 
> Spectral Gate can ignore the phase element of the real FFT results, and focus only on the amplitude. Gate (of a single FFT bin) is basically a pure amplitude operation.
> 
> I worked on porting a Spectral Gate effect from VST to AudioUnit in the early days of Mac OS X. The project never got finished, and I worried about the artifacts from altering sound in the frequency domain. This effect had the usual Gate threshold, but it was applied individually to each band. I recall that there was a way to measure the "noise" during "silent" excerpts of the audio, and this frequency domain curve was used to apply a different threshold to each bin of the FFT.
> 
> If I'm missing something about Spectral Gate that makes it more like Autotune than I've described, please point it out.
> 
> Brian





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