[sdiy] Novation peak NCOs

[Mike HEQX]

Xilinx says this about direct Digital Synthesis . "The core has optional 
phase offset capability, providing support for multiple synthesizers 
with precisely controlled phase differences." IS this something that can 
be changed in realtime through software or is it like a preset value. If 
it were changeable then it seems like it could be used for waveshaping.

I'm trying to get their ISE package running so I can mess with the 
technology . I have a long , long way to go before I understand what the 
heck is going on.


Mike


On 4/20/2017 7:45 PM, Scott Gravenhorst wrote:
> Interesting discussion.
>
> My first FPGA subtractive synth was a 4 osc with naive waveforms.  I did that because the
> DAC was capable of 1 MHz sample rate which I used.  Harmonics above 500 kHz are so low in
> amplitude as to be negligible.  I could portamento without siren fear.  The drawback was
> that it's 1 MHz DAC was also only 12 bits (the Spartan 3E Starter Kit board).  However, the
> 12 bit-ness didn't really seem to degrade it's sound.  But still, aliasing is aliasing and
> a good high sample rate is one of the cures.  It allows the simplicity of generating
> waveforms in a naive manner.
>
> Tom Wiltshire <tom at electricdruid.net> wrote:
>> 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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> -- ScottG
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> -- http://scott.joviansynth.com/
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