[sdiy] Digital accumulator VCO core?

Gordonjcp gordonjcp at gjcp.net
Sat Feb 13 00:18:12 CET 2021

On Fri, Feb 12, 2021 at 07:33:41PM +0000, Tom Wiltshire wrote:
> > 
> > If you generate a step, you generate aliasing and it's already down in your desired audio spectrum.  You'd need to run at some small number of MHz sampling rate, filter, and then decimate to 96kHz.  If you generate a naive sawtooth at 96kHz it'll alias like crazy in the low hundreds of Hz.
> > 
> The amazing thing for me is that if you generate that naive ramp with all that aliasing that folds down into the audio spectrum that you’ll hear, and then apply BLEP adjustments on the edges, it all miraculously disappears (well, nearly all - adjust to taste). That’s just remarkable!

This is the thing that's a bit like magic to me.  I can make it work, I kind of understand how it works, I just can't work out how it got there :-)

If you do a polyblep you correct the sample just before and just after the transition to "blend" the fractional-sample-position step into whole samples, but I don't get what the curve is supposed to be or how you design it.


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