SynthModules

> What are your opinions?

There are a couple of things at work. The ADC will dither at the 
bit boundary based on the mount of noise in the incoming 
signal. With the ADC scaled for one "count" per 10 millivolts (10 
volts/1024 counts) and typical analog noise at 1 millivolt RMS, 
about 60% of the input step will be "dither free". The problem will 
be most apparent with slow moving analog inputs. Also 
succesive approximation converters have what is called 
"aperature jitter" that also adds some dithering.

> Is an 8 samples average too much?

I think it is too much. Two sample averages, or four should be 
enough to solve the problem. Or reduce it to an acceptable level. 
It is too late for me to calculate the corner frequency, but it is 
simply the frequency where an output step is reduced by half.

> Is an update every 32 mS too slow?

Much too slow for music. A MIDI byte takes around 320 
microseconds, and three bytes make a "note on" each 
millisecond. But that means a 8 note chord has a bult in "flam" of 
8 milliseconds. Which some people claim to be able to hear.

Latency of under 3 milliseconds is considered good, but less is 
better. A rule of thumb is all channels should be updated within 1 
millisecond (for example the Buchla keyboards scanning speed 
is 1 millisecond divided by the number of keys). The PSIM will do 
that now with no averaging, so any averaging should be kept to a 
minimum.

If you want to hear some awful dithering, try a Roland OP8m CV 
to MIDI converter. The PSIM far out performs that with no 
averaging at all.