[sdiy] Novation peak NCOs

[Paula]

Tom,

That was my assessment pretty much.  
FWIW the NCOs in 002 run at around 700khz and use an external 8 bit parallel DAC  before the signal goes to the ladder filter.  
The monowave had ‎a 960khz update rate, again driving an 8 bit DAC. 

Paul‎a

Sent from my BlackBerry 10 smartphone.
  Original Message  
From: Tom Wiltshire
Sent: Saturday, 22 April 2017 00:16
To: James J. Clark
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] Novation peak NCOs


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


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