[sdiy] Prophet VS a phase accumulator design?

[Scott Nordlund]

> >Scott
> > I think the Evolver is not a great implementation of this.
> > The sample rate is too low (48 kHz?) to get away with the low
> > resolution wavetables and no multisamples, especially with all the FM
> > and stuff. It works for bass sounds and noise, and I understand it
> > wasn't really intended to be an all purpose high fidelity machine, but
> > it's not an ideal example to follow.
>
> That's what supriced me to, a 160Mhz DSP and semi crappy oscs!

Well, the delays aren't interpolated either. At least it's consistent.

> > I will say though that the early Casio Consonant-Vowel
> > stuff is nearly
> > great. The waveforms are very low resolution (16 steps) and
> > buzzy, but
> > very bright and clean. The HT series has a uniquely
> > excellent triangle
> > wave.
>
> Didnt the casios use the Ralph osc design, 600khz sample rate
> a 1 for up a zero for down? 1111100000=triangle?

I dunno what's going on in those ASICs, aside from the DPCM waveform
storage thing, but it's pretty impressive. 8 voice polyphonic purely
digital synthesis circa 1980. 
It's not like it can be directly 
compared to the PPG, but it 
certainly seems more "engineered".

Of course there are some considerable compromises and doubtless lots
of crude stuff happening inside, but the sound quality is pretty 
good. I wonder how the envelopes and amplitude scaling work.

They also had another "additive" chipset (something like 3 or 4
sine partials per voice with different envelopes) a little later
that was used in a few models (MT-70, Casiotone 501, 701 and 1000P),
but I don't think the sound was very interesting.


> > I saw the DSS1 service manual recently. It seems to use a
> > single multiplexed DAC, like the DW-8000. This would indicate a
> > fixed sample rate.
>
> Absolutely sure on that?
> Schemo/Manual says variable.

A true variable sample rate has to have a DAC for each oscillator. If 
it uses a single DAC, it's sequentially outputting each one. It can't 
do this asynchronously. So it's got to be, I guess, a time shared
fixed rate phase accumulator type thing.