[sdiy] Prophet VS a phase accumulator design?

[Scott Nordlund]

> What does he mean by phase accu eventually skipping codes?
> As in skipping table addresses?



Right, the phase increment is larger than one sample.



> >The ESQ-1 DOC chip I thought did something different, I have a feeling
> >that "drops" samples as you reach higher octaves.
>
> ICS1261 data sheet (24bit phaseacc) suggest one could set table width
> i.e shorter tables like DW8000 on the fly but apparently ESQ uses
> different tables for each octave, which sounds like table BW?!



The ESQ should be similar to the DW8000, only with a sample every 8

semitones or so, depending on waveform, and much shorter waveforms. 

The ESQ has a lot more audible aliasing than the DW-8000.



My understanding of it is this: I believe the PPG and Prophet VS are 

fixed sample rate, but with much higher rates (in the hundreds of kHz

range), so they can more or less get away with a single waveform over

the entire keyboard without too much aliasing. Synths like the DW-8000

and ESQ use a lower sample rate (50 kHz or so), so they need to use 

multisamples. 



But the difference between fixed and variable sample rate becomes a 

little arbitrary at high rates. Variable sample rate systems that 

aren't clocked by a VCO derive their clock from a programmable 

divider, in which case you can say that the clock source (crystal 

oscillator or whatever) is the "true" sample rate, only the phase

increments are always one sample and constrained to integer divisions

of the clock frequency. It's trading aliasing and jitter for high

frequency pitch resolution.