[sdiy] Simple DSP as VCO substitute (was Re: CEM3340 reissue)

[Vinicius Brazil]

Hi,
In my 6 years old VCO Module (AetherOscillator) I use the dsPIC33FJ128GP802
but with a external DAC.
I had many problems with the internal DAC and the maximum sample rate is
100KHz.

http://www.vbrazilsystems.com/aether-oscillator.html

Some demos & tests involving Aether Oscillator:

https://soundcloud.com/vinicius-brazil/as1-demo34-crossfm2
https://soundcloud.com/vinicius-brazil/as1-demo28-sequencia-semi
https://soundcloud.com/vinicius-brazil/as1-demo27-acusticbass
https://soundcloud.com/vinicius-brazil/as1-demo9-aetheroscillators
https://soundcloud.com/vinicius-brazil/as1-demo3-assobio
https://soundcloud.com/vinicius-brazil/as1-demo6-sequencia1
https://soundcloud.com/vinicius-brazil/as1-demo7-sequencia2


On Tue, Jun 14, 2016 at 3:39 PM, <sleepy_dog at gmx.de> wrote:

>
> Square wave on the DAC?
>
> Would it not be enough to just do that with a harwdare PWM channel?
> It did sound nice enough at first "glance" when I tried it, but I'm not
> sitting on a pile of signal theory to know what I'm doing there ^^
> I mean including PWM. I.e. directly using a PWM timer output swinging at
> the pitch you want to play, LFO-modulated in the firmware - sure, the PW
> resolution varies depending on pitch, but it sounded nice enough to me.
> Between the low end and 7 kHz. I have not looked at the spectrum or would
> know how that of a typical synth pwm should look like, though.
>
> But if you could do that, then you'd have 3 waveforms on the dac, plus
> PW-variable square.
>
> Is the F303 + needed parts & PCB still cheaper than the other options,
> though? (I have no idea what the old chips cost)
>
> Steve
>
>
>
> Am 14.06.2016 um 20:00 schrieb Vladimir Pantelic:
>
> STM32F303 has 3 12-bit DACs and a ton of 12 bit ADC channels. so saw,
> square, triangle and sine via an external shaper for extra grit :)
>
> On Jun 14, 2016 7:54 PM, "Tim Ressel" < <timr at circuitabbey.com>
> timr at circuitabbey.com> wrote:
> >
> > Two DAC output yields 2 waveforms. I'm thinking sine and triangle. A
> digital out pin can make squares and PWMs, or a comparator can handle it.
> If you make triangles rather than sawtooths then the DAC holds together
> better at higher frequencies. It is a simple matter of converting a tri to
> a saw externally.
> >
> > I don't see 12 bit ADCs as much of a limitation. It should do V/Oct out
> to 10 octaves.
> >
> > --TimR
> >
> >
> > On 6/14/2016 10:40 AM, Tom Wiltshire wrote:
> >>
> >> On 14 Jun 2016, at 16:44, Tim Ressel < <timr at circuitabbey.com>
> timr at circuitabbey.com> wrote:
> >>
> >>> Speaking of doable, it should be possible to take a DSP chip and mimic
> the function of a 3340. Yes I know, the 3340 has "that sound". But it also
> has "that price". I'm thinking the DSPIC33FJ128GP802. It comes in a 28 pin
> dip and has built-in audio DACs. Might be interesting.
> >>
> >>
> >> The idea had occurred to me too, for the same reasons - the dsPIC
> 33FJ128GP802 is about the right size and format to make a good analog
> oscillator substitute. It has two DAC channels, so maybe even a dual
> oscillator would be possible.
> >>
> >> There are definitely limitations with the chip (only six 12-bit ADC
> inputs when using the DAC, for example), and moving to a digital chip
> implies doing certain things differently (you won't get multiple waveform
> outputs in parallel, for instance). It's a good idea, and one I've played
> with quite often, but never been happy enough with the result. That won't
> stop me trying again though.
> >>
> >> In some ways, I think it might make more sense to go in the direction
> of my 8-bit PIC VCDO and give up with pure virtual analog and accept that
> you can do a better job if you don't try and be something you're not.
> Perhaps it should be a voltage-controlled digital oscillator chip, doing a
> few of the interesting things you can do digitally instead of trying to do
> anti-aliased analog waveforms with hard sync and PWM and so forth.
> >>
> >> Tom
> >>
> >>
> >>
> >
> > --
> > --Tim Ressel
> > Circuit Abbey
> > timr at circuitabbey.com
> >
> >
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