From: Haible_Juergen#Tel2743 Subject: AW: OB-8 EGs Date: Fri, 12 Jan 96 10:25:00 PST >The EG's on the OB8 are analogue - both envelope generators had Software >calibration parameters stored within the OB8 memory, these were used to >match envelopes on all OB8's to the same standard - these parameters can >( and should ) be saved by tape dump incase your OB8 fails ( although the >Oberheim engineers thoughtfully provided a 'get-you-going-again' routine >that re-aligns the EG's to a basic level via a special button sequence ). >There are some 2nd panel EG's that are software controlled - I think? >they're something to do with the LFO, but I honestly can't remember - >JH??. > >Clive The OB-8's main EGs are analogue, using some Curtis Chips. Besides the mentioned calibration parameters, there is another trick performed by software on the filter envelope. It took me a while to understand this - when I saw the schematics first, I thought "Where the hell is the VCA that controls the filter envelope amount ??". They really left it out, and scaled the envelope parameters instead. I would have to look it up at home, if You want to know the exact details, but it's kind of reducing the peak level of the ADSR chip by an external voltage for amounts other than maximum, and adjusting other parameters (sustain, ...) accordingly. I guess they could do this because they had the offsets calibrated out exactly. I am quite astonished how good it works, though I haven't measured the minimum possible amount. The important thing is that You don't slow down the envelopes by this means, so the OB-8 incorporates the best of both worlds: digital accuracy and analog speed. (And of course those clever Oberheim engineers have found another spot to reduce the price compared to the OB-Xa!) The 2nd page envelopes are software generated and intended for the LFO modulation amounts. You can modulate the groups PWM1/PWM2/AM and FM1/FM2/filterMod with separate envelopes, and You can also assign one of them to the LFO *rate*. Normally, these envelopes are delayed ramps, i.e. a "DAR" with variable Delay, variable Attack, but zero Release. But You can invert them; then it's more like a trapezoid, or a "AHD" with zero Attack, variable Hold time, and variable Decay. But that's not all. As You can make the LFO real slow and sync it to every keyboard trigger, You may also apply these envelopes to a nearly constant voltage (i.e. sloooow rectangle), using the envelope directly for pitch modulation a la Roland. (Instead of using the filter envelope, the amount of which is locked to the filter modulation amount) ... have to stop now. Speaking about my favorite synth always takes me away (;->) Hope this helped, JH.