[sdiy] Novation peak NCOs

[Bruno Afonso]

If only some notation engineers were allowed to speak freely about the
design instead of the marketing people...
On Sat, Apr 22, 2017 at 07:14 Richie Burnett <rburnett at richieburnett.co.uk>
wrote:

> I think confusion is caused by the use of the term "oversampling" in the
> online article. It's not *oversampling* anything, it's just *the sampling
> rate* like you said Tom.
>
> -Richie,
>
> Sent from my Xperia SP on O2
>
> ---- Tom Wiltshire wrote ----
>
> >I've watched the interview and read the article again, and they're pretty
> explicit about saying that they're generating the oscillators and the
> envelopes and LFOs at 24MHz. They describe that as the "sample rate"
> several times. They do say that it's converted to a 1-bit output, but
> that's just the output - (probably downsampled at that point?)
> >
> >So, no, I don't think it's a 375KHz or similar sample rate, although I
> was convinced briefly there for a moment. They say clearly it's 24MHz, so
> it's 24MHz. Richie's right.
> >
> >Tom
> >
> >
> >
> >On 22 Apr 2017, at 00:25, Richie Burnett <rburnett at richieburnett.co.uk>
> wrote:
> >
> >> James J. Clark 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.
> >>
> >> Have a listen to the interview with one of the Novation designers about
> Peak on the Sonicstate website from Superbooth. He reveals more details and
> states that the oscillators and LFOs run 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 think you misread the document you linked to. It states that the
> waveforms *don't need to be band-limited* in Peak because they are being
> generated at 24MHz. Quoted below from the Novation website:
> >>
> >> " On a conventional digital wavetable-based synthesiser, the waveforms
> are band-limited before being stored in the table. This is to avoid
> unwanted aliasing. With the New Oxford Oscillator design there is no need
> for band limiting; the extreme oversampling means that the aliasing problem
> is pushed way out of the audible frequency spectrum enabling Peak to
> utilise mathematically pure waveforms."
> >>
> >> -Richie,
> >>
> >> ---- James J. Clark 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).
> >>>
> >>> They call this the "New Oxford Oscillator". I don't see what is
> >>> particularly new about this. Maybe there was an old Oxford oscillator?
> >>>
> >>> In any case, the Cylonix Cyclebox (and the Cylonix-Intellijel
> >>> Shapeshifter) is an FPGA design and DOES run the signal path at 24MHz
> and
> >>> has all the nice properties that other posters have mentioned, such as
> >>> inaudible aliasing and ability to do artifact-free FM (and also
> >>> complicated nonlinear operations which would otherwise cause heaps of
> >>> aliasing). And this was released back in 2010...
> >>>
> >>> Regards,
> >>> Jim
> >>> www.cylonix.com
> >>>
> >>>
> >>>
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