[sdiy] Novation peak NCOs

[paula at synth.net]

You should be able to route things to the phase offset, like other NCOs 
and so on, so you could build something akin to the older casio phase 
distortion synths :)

On 2017-04-21 02:17, Mike HEQX wrote:
> 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
> ________________________________________________________________________
> -- Scott Gravenhorst
> -- http://scott.joviansynth.com/
> -- When the going gets tough, the tough use the command line.
> -- Matt 21:22
> 
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