[sdiy] In praise of the ATM STM32F303

[Richie Burnett]

Olivier, thanks for sharing the details!

> 16384 16-bit words, Q4.12 (converted to/from float during processing -
> ie the memory 16-bit word stores x * 4096.0f).

How do you think it would sound with percussive sounds like drums? Can you 
hear any periodic cycling of the energy around the reverb tank with such a 
small amount of delay memory?  I thought I read somewhere that Keith Barr or 
Jon Datorro or someone said you ideally need more than a second of memory 
for the reverb tail to be perceived as desirably "evolving" rather than 
undesirably "fluttering".  I haven't played with this stuff much though.  It 
seems like percussive sounds like drums would be quite demanding of the 
reverb algorithm.  After all, most of the early Midiverb reverb tails used 
to ring like hell with percussive sounds.  I've also got a powered 
mini-mixer here with built-in reverb, which I guess is one of those spin 
semi chips or an AL-something_or_other DSP from Alesis (haven't looked 
inside,) which also sounds very metallic with drums.

> I don't remember if this is because I needed a bit of headroom, or if
> I liked the "wash" of the truncation noise I got. Probably a
> compromise between both.

That's exactly the compromise that I was thinking off.  I know the early 
Midiverbs and the like used to use 16-bit memory and were really noisy.  I 
always thought that was because of accumulated noise in the iterative 
algorithm, but the 16-bit ADCs probably produced about 4-bits worth of noise 
in those days!

> Originally, I tried to use the same kind of 14-bit floating point
> format used in the FV-1 (since I used the FV-1 to prototype the
> effects in Clouds/Elements), but the decompression/compression was
> extremely costly.

I can see the advantage if the floating-point memory 
compression/decompression is implemented in hardware, but did wonder about 
the benefit.  After all it's more bits of resolution in the mantissa that 
you need to stop noise building up from quantisation, not more bits in the 
exponent.

-Richie,