[sdiy] In praise of the ATM STM32F303

[Simon Brouwer]

Hi Eric, 

Any idea whether that noise is due to worse (differential) linearity or to worse
crosstalk from digital circuits? 

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.

Best regards
Simon

> Op 13 februari 2016 om 4:37 schreef Eric Brombaugh <ebrombaugh1 at cox.net>:
> 
> 
> A couple guesses why:
> 
> 1) for high-volume production such as Waldorf usually does, every cent makes a
> difference. In large quantity F3 parts like the 303 are a few bucks cheaper
> than F4 parts, so that adds up.
> 
> 2) I've used both F3 and F4 parts in products so I've got some experience with
> them. The F3 parts analog sections are considerably higher quality than the
> F4. Noise on F3 ADCs and DACs are a few lsbs lower amplitude than F4 parts.
> 
> Eric
> 
> On Feb 12, 2016, at 8:29 PM, Declare Update wrote:
> 
> > Really loving this thread! I'm curious though: why do you guys think Waldorf
> > chose this chip? It's not particularly cheap, they could have had an F4
> > running much faster with more ram for very similar cost. Were F4 parts with
> > built in DACs less common at the time, maybe? 
> > 
> > A few months ago, I had a great time trying out reverbs on a Teensy 3.1. I
> > had the main feedback loop going from the dac out to a spare adc channel,
> > which gave me a few free samples of delay and the chance for simple passive
> > analog filtering. made a huge difference on simple algorithms.
> > 
> > Playing with the STM32F446 now, and it's a real treat in comparison. 
> > 
> > 
> > Chris
> > 
> > Sent from my iPhone
> > 
> >> On Feb 12, 2016, at 4:00 PM, Gordonjcp <gordonjcp at gjcp.net> wrote:
> >> 
> >>> On Fri, Feb 12, 2016 at 09:01:50PM -0000, Richie Burnett wrote:
> >>> Did you base it on the Jon Datorro "Lexicon Plate" reverb algorithm
> >>> too?  Or one of the Spin Semiconductor FV-1 algorithms?  Or
> >>> something you designed yourself?
> >> 
> >> I based it on
> >> https://ccrma.stanford.edu/~jos/pasp/Schroeder_Reverberators.html
> >> and a lot of fiddling and guesswork
> >> 
> >> This is the floating point version - I can't seem to find the fixed-point
> >> one, which may be on my spare laptop.  It uses longer periods but the
> >> fixed-point one uses 2048-word delays.
> >> 
> >> https://github.com/gordonjcp/reverb
> >> 
> >>> I know the early Reverb pioneers had to be really clever in making
> >>> their algorithms make the best use of what limited (expensive!)
> >>> memory they had available to them back then.  With only a small
> >>> amount of delay memory you have to use lots of diffusion to scatter
> >>> the energy around each time it passes around the loop otherwise you
> >>> hear audible repetitions.
> >> 
> >> Mine has a distinctive "rattle" at certain settings, and certainly sounds a
> >> lot better on sounds with a relatively slow attack and decay.  That being
> >> said, the "bittiness" seems to be lost with busy drum patterns.
> >> 
> >> -- 
> >> Gordonjcp MM0YEQ
> >> 
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