[sdiy] In praise of the ATM STM32F303

[Eric Brombaugh]

On 02/13/2016 04:05 AM, Simon Brouwer wrote:
> I am starting out with the STM32F446 for a one-off semimodular monophonic synth,
> and was thinking of using one of its built-in DACs for VCO control voltage. My
> plan is to deal with its nonlinearities by calibrating its output voltage at
> each semitone, then using a lookup table with correction values.
> But if the DAC output voltage contains LSB's of uncorrelated noise, I may be
> better off using an external SPI DAC.

Sorry - I neglected to address your question about the F4 on-chip DACs:

I don't have a lot of experience using the F4 DACs. I've tried them out 
on development boards and they seemed to work, but I didn't analyze the 
audio quality, especially the noise at low levels as I have done on the 
F373 system I did. I don't have any experience to suggest they won't 
work well, but YMMV - I'd suggest trying them out with a devboard, but 
bear in mind that most devboards aren't designed with quality analog 
circuitry so the results may not represent the best performance you 
could get from the part. To know for sure you should design a board with 
good layout and separately regulated analog supplies.

For best results, it's fairly easy to use the I2S or SAI peripherals on 
the F4 parts, coupled with an off-chip audio-quality DAC. SPI works too, 
but I2S DACs are readily available and fairly inexpensive compared to 
similar-resolution SPI DACs which are typically built to stricter 
specifications on gain and offset errors which don't have much effect on 
audio performance. Plus, I2S audio DACs often have built-in oversampling 
and reconstruction filters to reduce the amount of external analog you 
need to add.

Eric