[sdiy] Novation peak NCOs

[Tom Wiltshire]

Ok, so let's just have a look at that for a moment.

Assume a highest output frequency of 20KHz (I wouldn't even be able to hear this). We've got a nyquist frequency of 12MHz. That means that only anything that goes far enough over 12MHz to alias all the way back down below 20KHz is actually going to be audible. So that's 23.98MHz before we get audible aliasing. That's equivalent to the 1199th harmonic of  20KHz ramp wave.

It's a high enough frequency they can ignore aliasing, even for naive waveforms, and even for tough cases like ramps and squares.

It does seem like overkill, but FPGAs are cheap these days, and running a few (or a lot of) NCOs isn't even going to make one break a sweat.

Yeah, why not? I like it. Simple, direct, does the job.

Tom

On 20 Apr 2017, at 18:20, Richie Burnett <rburnett at richieburnett.co.uk> wrote:

> An interesting direction Novation are taking with the use of FPGA based NCO oscillators on their new hybrid polysynth. There's a video from Superbooth about it on sonicstate. It uses a sample rate of 24MHz to generate classic analog saw, pulse, tri waves, etc, then feeds them through conventional analog VCF, VCA, etc.
> 
> Seems like a bit of a brute force way to crack the old aliasing nut, but I guess it gives them the ability to do some wacky audio rate modulation stuff with reduced aliasing too.
> 
> -Richie,
> 
> Sent from my Xperia SP on O2
> 
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