[sdiy] [synth-diy] numerically controlled superoscillator without hard sync

[cheater00 .]

On Sun, Feb 9, 2014 at 10:59 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> On 9 Feb 2014, at 20:32, Mattias Rickardsson <mr at analogue.org> wrote:
>
>> On 9 February 2014 18:08, cheater00 . <cheater00 at gmail.com> wrote:
>>> The variable sample rate oscillator could also contain things like
>>> filters and other stuff. A whole VA could be implemented, and aliasing
>>> is not an issue at all.
>>
>> Multiple oscillators per voice is nice, at least so I've heard. ;-)
>> Could this be incorporated without having to duplicate everything?
>
> No, not really. A variable sample rate system would require different sample rates for different oscillators. Otherwise you're back where you started with the same problems as fixed sample rates. You need as many "sample rate clocks" as oscillators - these are your high frequency square-wave-only VCOs.

As described between me and Brian, you can use buffers and IRQ or DMA
to have multiple asynchronous systems running off one synchronous
system.

>> And how about other behaviours that makes oscillators have tricky
>> frequencies... like PWM, where the oscillator is still but the
>> percieved pitch varies due to the modulation. How does the harmonic
>> aliasing behave there? Is all still well?
>
> Yes. You can either cross-fade between different width band-limited pulse waves in waveform tables (which is indistinguishable once you get to 32 waveforms or so) or you could generate non-band-limited PWM and accept the harmonic distortion.

You can also have two band-limited ramps at low sample rates and
offset them by fractions of a sample.

Cheers,
D.