[sdiy] [synth-diy] numerically controlled superoscillato without hard sync

[Paul Burns (Fitvideo)]

Slightly OT but in regard to Csound, there is a guy on Muffs who has created
3 x 2-op fm oscillators that respond to pitch and are tuneable against each
other, using this module.

http://www.qubitelectronix.com/#!nebulae/c23nm


http://www.muffwiggler.com/forum/viewtopic.php?t=104514&start=all&postdays=0
&postorder=desc

cheers and regards

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Declare Update
Sent: 09 February 2014 20:13
To: Jim Credland
Cc: synth-diy
Subject: Re: [sdiy] [synth-diy] numerically controlled superoscillator
without hard sync

I have recently been pondering this same idea! I was thinking you'd have a
pin change trigger an ISR, which just increments the index to a wave table.
So you're driving vco would have to be the size of your array * desired
frequency. Clocking the actual micro is an option i guess, but as Tom points
out, that's pretty fast!

You mentioned doing a whole VA this way, would that be with separate
processors for each unit? How would you go about this?


Sent from my iPhone

> On Feb 9, 2014, at 12:38 PM, Jim Credland <jim at cernproductions.com> wrote:
> 
> I spent some time creating tones in csound with additional aliased
overtones (i just added a sine wave and calculated the frequency) - it
sounded great - though that approach wouldn't have worked with complex
waveforms very easily.
> 
> Also, the Tip Top Audio Z-DSP lets you do this type of thing.  You can
clock the DSP chip with another oscillator.   I've not tried driving it with
a melody yet though - that might be pretty interesting.
> 
> I'm going to try it right now!
> 
>> On 9 Feb 2014, at 17:08, cheater00 . <cheater00 at gmail.com> wrote:
>> 
>> Hi,
>> 
>> thinking about this recently, one could use a high-frequency 
>> oscillator, and use it as the clock for a microcontroller which 
>> assuredly outputs a single sample every n clocks. This way you can 
>> perform VA style synthesis where the time base is derived from an 
>> analog oscillator that can perform FM and other neat analog tricks. 
>> On the other hand the uC only has to synthesize at a single 
>> frequency. So say it's always synthesizing at A440, and you change 
>> the pitch by changing how fast it executes its algorithm, i.e. by 
>> changing the clock, i.e. by changing the sampling frequency. This 
>> way, externally (i.e. at the output of the DAC) the aliases are 
>> always precisely at the same position in relation to the base 
>> frequency of the note being played. The aliases become part of the
timbre, enriching it.
> 
> 
>> This is
>> in contrast to aliasing in a system where the sampling frequency is 
>> fixed, and the pitch of the note being synthesized is changed in the 
>> usual way. In this case, which doesn't happen here, the aliases are 
>> at a different position for every pitch, and therefore the oscillator 
>> not only plays your desired melody, but also a quieter, undesired 
>> melody which is completely out of tune and works against your music.
>> 
>> The variable sample rate oscillator could also contain things like 
>> filters and other stuff. A whole VA could be implemented, and 
>> aliasing is not an issue at all.
>> 
>> The only thing you need to ensure is that your reconstruction filter 
>> works well with a variable sample rate.
>> 
>> Cheers,
>> D.
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