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Square wave on the DAC?<br>
<br>
Would it not be enough to just do that with a harwdare PWM
channel?<br>
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 ^^<br>
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.<br>
<br>
But if you could do that, then you'd have 3 waveforms on the dac,
plus PW-variable square.<br>
<br>
Is the F303 + needed parts & PCB still cheaper than the other
options, though? (I have no idea what the old chips cost)<br>
<br>
Steve<br>
<br>
<br>
Am 14.06.2016 um 20:00 schrieb Vladimir Pantelic:<br>
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cite="mid:CADBCB7Hyc4VFcCfDUqabEtE_=BucxtLm-_Ns9GPuxAwDM1Lm=g@mail.gmail.com"
type="cite">
<p dir="ltr">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 :)<br>
</p>
<p dir="ltr">On Jun 14, 2016 7:54 PM, "Tim Ressel" <<a
moz-do-not-send="true" href="mailto:timr@circuitabbey.com"><a class="moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a></a>>
wrote:<br>
><br>
> 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.<br>
><br>
> I don't see 12 bit ADCs as much of a limitation. It should
do V/Oct out to 10 octaves.<br>
><br>
> --TimR<br>
><br>
><br>
> On 6/14/2016 10:40 AM, Tom Wiltshire wrote:<br>
>><br>
>> On 14 Jun 2016, at 16:44, Tim Ressel <<a
moz-do-not-send="true" href="mailto:timr@circuitabbey.com"><a class="moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a></a>>
wrote:<br>
>><br>
>>> 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.<br>
>><br>
>><br>
>> 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.<br>
>><br>
>> 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.<br>
>><br>
>> 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.<br>
>><br>
>> Tom<br>
>><br>
>><br>
>><br>
><br>
> -- <br>
> --Tim Ressel<br>
> Circuit Abbey<br>
> <a moz-do-not-send="true"
href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a><br>
><br>
><br>
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