[sdiy] Digital accumulator VCO core?

Vladimir Pantelic vladoman at gmail.com
Wed Feb 10 11:28:32 CET 2021

On 10.02.21 09:40, Gordonjcp wrote:
> On Tue, Feb 09, 2021 at 09:34:00AM +0000, Tom Wiltshire wrote:
>> There was someone here some years ago who’d done a voltage-controlled oscillator on a dsPIC. The cunning part of that was that the output waveform was a triangle instead of a ramp. That massively reduces the aliasing problems, and since triangle-core oscillators are common, there’s a lot of wave shaper designs you can tack on the end. But the exponential conversion was done inside the chip for obvious reasons. The ADC sample rate was fast enough for it to do convincing FM.
> Here's a really simple one on an Arduino that generates an antialiased saw at about 32kHz sample rate.
> https://github.com/ErroneousBosh/slttblep

this line gives me physical pain:

  theta = pow(2,32) * adc / ref;  // calculate phase shift per sample

but then, what's a double precision floating point exponential function,
a multiplication and a division on an 8 bit CPU between friends ;)

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