[sdiy] D50 a VA or not?

[karl dalen]

Little are known to the public on how the D50 works, so i had this brief
conversation with a former Roland R/D manager on that item i asked as a
shot in the dark if it was just table reading for the osc's and some
kind of simple ASIC DSP for the filter TVF.

He replied that the D50 was a real VA based upon clever table manipulation
to simulate the filter effects, that was also the reason PCM samples could
not go trough the table process (TVF). (Presuming the entire wave would be
screwed up!)

So the TVF in the D50 appears not to be a filter at all, rater relabeled
to set the user into believing it was! So assuming the following (might be wrong or right i don't know) the D50 has two cyclic waves, Pwm and Saw, the
Pwm are created out of a sine lookup table, Xor'ing or something then goes
trough this TVF thing, then the Pwm are multiplied and shifted with the
Sine to create a double freq SAW and that's it? Since the Saw are flipped
up so are also the Pwm's lower edge resonance emulation and everything
looks neat and tidy.

So i did some initial tests, i took 2 oscillators one Square and one Sine
2x- freq and phase locked to the Square front edge who also triggered an
AD who shaped the amp of the Sine to get the log resonance curve and then
simply added these two and then swept the freq of the Sine and sure it
sounds exactly like a mid open filtered Square with resonance.

I assume some correlation between the amplitudes of the Square and Sine
during play time to satisfy the emulation of a closing filter effect
must also be in place somehow, or some phase shifting thing to get
Sine dominat in amplitude over square during lowering of center
frequency to emulate a closing filter?

So a partial in the D50 could be made up of one table osc creating
the actual tone and one sine table osc to create the resonance/filter?

1:So digital guru's what do you think about that D50 thing?

2:And what really defines à VA instrument? I had thought a mirco running
a algorithm that simulates analog functions was regarded VA, i.e computes
the function, not by fetching data from predefined tables, or similarly?