What, really, is the difference between SCI Pro 1 and P5?

[madtheory]

Just read a Vince Clarke interview where, again, they mention he has a P5, and then he says the Pro 1 is his favourite because of "fast envelopes". Surely the Pro 1 is the same as one voice of a rev 3 P5? And wouldn't a Pro 5 be better because it has memories? They both use the same envelope generator chip, CEM3310. I notice he nearly always keeps the P5 under the Matrix 12 on the wall behind his main workstation, the Pro 1 is off somewhere more remote...

[desmond]

I think the general misconception is that the P1 is one voice of a P5, but I don't think it's the case.

Might be worth giving Urs a shout who is deep into modelling the Pro-1 (for "Repro") as it was his first synth and is quite special - he's probably deep in the guts of the thing.

But yeah, I think the Pro One does sound different to a P5 voice.

[madtheory]

Thanks I'll ask him. Maybe the keyboard scanning in the Prophet 5 makes it slower to trigger after a key strike, even though the EGs are identical?

[desmond]

Thanks I'll ask him. Maybe the keyboard scanning in the Prophet 5 makes it slower to trigger after a key strike, even though the EGs are identical?

Or it might be some compromises were made in the P5 design because of the nature of polyphony... I'm sure I've read some stuff on this in the past, somewhere...

[Sir Ruff]

I imagine the main difference is the gain structuring between the two. Polyphony probably requires each voice to be less loud/aggressive. Who knows about the envelopes, unless the P5 CPU somehow slows things. But tbh, I really wouldn't consider VC's qualitative opinion over some actual technical comparison. He knows what he likes, but he's never struck me as really understanding the inner workings of, or differences between his gear.

[commodorejohn]

Thanks I'll ask him. Maybe the keyboard scanning in the Prophet 5 makes it slower to trigger after a key strike, even though the EGs are identical?

This seems plausible. I'm not sure what the clock rate on the P5's CPU is, but the Z80 isn't a particularly fast chip clock-for-clock. Granted, the Pro-1 still has plenty of panel controls to handle, but with fewer keys to scan and no need to do any particularly nuanced voice-assignment handling, I could imagine it making something of a difference.

[meatballfulton]

I don't think the Pro One scans the keys...not really needed in a mono synth after all.

[ApolloBoy]

I don't think the Pro One scans the keys...not really needed in a mono synth after all.

Looking at the schematic it looks like the keyboard is scanned by an 8021 microcontroller which is also responsible for controlling the arpeggiator and sequencer. That seems to be the only computer-controlled portion of the Pro-One, there's no scanning of the front panel and no Z80 CPU like the Prophet-5.

[madtheory]

Thanks ApolloBoy for that info, spot on

I imagine the main difference is the gain structuring between the two.

Good theory, I just had a good look at the schematics. They both use the CEM 3280 VCA (P5 uses 14 of them not all in the audio signal path), but as far as I can see, the P5 has one extra VCA in the audio signal path as a buffer for the 5 voice mixer, and to allow CV/foot pedal volume control. So I guess that could create more distortion? Would that make the Pro One sound "faster" though?

[Sir Ruff]

Actually, I wonder if all the VCAs--or simply that final VCA--affect things somehow. On the Polysix there's a final filter after the effects section that ultimately slows the envelope response time somewhat. The more VCAs that are in the signal, it seems that the response time could also be affected?

But I'd want to see some actual numbers or a scope readout first to know that there really was a difference before speculating further (we're kind of doing this in reverse!)

[madtheory]

How is a VCA going to slow things down? It's just an amplifier that can take a CV for level control. Used as the summing amp, there's no envelope.

[CfNorENa]

Can't comment on the technical side of this (but I think Sir Ruff is probably right), but I did have both in the studio for a bit, and in my experience the Pro-1 was definitely stronger and punchier than the Prophet 5 (rev 3). I had to sacrifice the former to be able to afford the latter, and am still happy with that move, but the P5 (my favorite synth, by the way) doesn't quite have the power of the P1.

[desmond]

From Urs recently:

"The Mod Matrix of the Prophet 5/T8/600 whatsoever is a piece of cake in comparison. It's really just the Pro-One that has these extraordinary capabilities - which pose a vast challenge in software."

The P1 seems to have much wider range in the modulation capabilities, another reason it's not just one voice of a P5...

[madtheory]

It's quite possible the extra VCA is clipping the attack, or something like that, and not in a good way. Not sure if wider mod range would give a similar impression- I doubt it. I wonder why the mod range is wider? Maybe they scaled it down on the digitally controlled synths because 8 bit wasn't enough to capture the full range without too much quantising? Seems likely, given Urs's issue with it even in a 32 bit float environment.

[desmond]

If you're interested, have a read of the various RePro threads on KVR, where he goes into detail why the Pro-1, compared to many other analog synths, is such a challenge to model. Lots of info there...