I hope this doesn't become tumble2k's Prophet '08 rant thread, but I thought I'd report on some more of my findings as I play with this amazing machine.
On slop:
I was playing the T8 Strings preset and tweaking it to my taste: enabling velocity sensitivity, disabling aftertouch, turning down the voice volume, which smooths out the filter, etc. When I was able to control it right I started playing some string pieces. Hmmm. Someone is playing out of tune. Is this high school orchestra? Oh yeah, slop! The slop was set to 2 or 3. I turned it to 0 and ... okay this sounds more professional! I think Sacred Synthesis said that slop recreates the worst quality of an old vintage synth, and I definitely agree.
On VCOs
I went to the local guitar center to play the Prophet 6 and the OB-6. The Prophet 6 struck me as an incredible keyboard. Everything I played sounded nice ... kind of the way a Moog always sounds nice. Very different from the '08! On the '08 you need to work for the good sounds. I have heard discussions about the sweet spot on the two instruments and now I understand what they mean.
Anyhoo ... I decided to take a careful listen to a single unadorned sawtooth and then a pair of sawtooths on the P6. I observed the following:
1. The single sawtooth on the P6 sounded pretty similar to the P'08's sawtooth, except it was maybe a little darker (but it could have been the sound system)
2. When there are two sawtooths running on the P6 with no detune, they always beat against each other. This is different than the P'08.
The same was true with the OB-6.
A bit discouraged, especially after my experiments with injecting noise into the DCO frequencies on the P'08 that turned out badly, I went home and played the P'08. Using a random LFO still sounded lumpy or burbly. On a whim I tried to use a reverse sawtooth LFO with a rate of 136 (about 120 Hz) and an amount of 1, the lowest possible.
Jackpot! The single sawtooth sounded pretty much the same. But when I combined two they tend to beat a little even with no detuning and no slop. The combined sound was very reminiscent of what I had heard from the Prophet 6.
I'm going to use the basic patch with these two LFOs, detune set to 0, and slop set to 0 as the starting point for my "VCO simulation" patches in the future.
I'm following mefistophelees's footsteps here. He said to experiment with rates and waveforms for the LFO. I think this works rather well. The reverse saw is a little like the ripple on a power supply (which is why I chose the LFO frequency of 120 Hz). I wonder if that has anything to do with anything.
Samples attached. First phrase is done with no detuning and no LFO modulation. The second phrase is done with a fair amount of detuning and no LFO modulation. The third phrase has no detuning and LFO modulation.