[sdiy] Novation peak NCOs

[Tom Wiltshire]

On 21 Apr 2017, at 23:15, James J. Clark <clark at cim.mcgill.ca> wrote:

> Regarding the 24MHz issue, the documents that I have read on the Peak (https://uk.novationmusic.com/peak-explained) only say that the DAC is oversampled to 24MHz, which is pretty typical for sigma-delta style audio DACs these days. Its a way to get high bit widths - typically 16 or 24 bits. It does NOT mean that the signal processing is done at 24MHz. In fact the "peak-explained" document specifically says that the wavetable waveforms are band-limited before being stored in the table, to avoid aliasing. This wouldn't be necessary if the signal path was running at 24MHz.
> 
> I would guess that the signal path is running at whatever the DAC sample rate is (which is not 24MHz - that is just the master 1-bit clock rate).

Yes, I wondered about that. Thanks for clarifying.

So we're thinking this is an FPGA synth design with some high-but-not-extraordinary sample rate, that then uses a 1-bit DAC run-in at 24MHz for output. x64 oversampling is common for this type of thing, so let's assume that for a moment - that gives us a 375KHz sample rate, roughly twice the 192KHz rate we're more used to.

Is that a fair summary? Is that what we think they're up to?

Tom