Page 1 of 1

Oberheim Xpander - "slow" envelope rectification

Posted: Thu Feb 10, 2011 7:33 pm
by Sir Ruff
Having been convinced, and having convinced myself that the Xpander will always have eternally slow envelopes, I thought I'd give it a whirl and see how "fast" I could make them. The key is cutting out as much modulation as possible and even using one envelope for both filter and amp (later I used two seperate ones). Ramps can be used too, but I find they don't really sound as good as a straight envelope.

It's no mini or pro-1, but I think it does a perfectly adequate snap-bass - better than I imagine most people would expect. Not sure on actual envelope attack speeds - definitely more than a few milliseconds - but it sounds fine. One benefiting factor is that the xpander (like other obie's) does not lose much bass even at high rez, so it has a good oomph regardless.



(mods, if this is listening lounge material, please move it, but I figured it was more of a discussion maker than demo)

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Fri Feb 11, 2011 12:09 am
by Juno6
Thanx for the demos.

They´re not that fast anyway, but they´re usable. I had an Xpander, it´s better for
other purposes.

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Fri Feb 11, 2011 3:39 am
by StepLogik
They are calculated in software and I'm sure the CPU is plenty busy with all those modulation sources and routings! The Xpander actually has a CPU dedicated to this function in addition to other tasks related to controlling analog guts such as background calibrations.

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Fri Feb 11, 2011 9:57 am
by SWAN
Sir Ruff wrote:Having been convinced, and having convinced myself that the Xpander will always have eternally slow envelopes, I thought I'd give it a whirl and see how "fast" I could make them. The key is cutting out as much modulation as possible and even using one envelope for both filter and amp (later I used two seperate ones). Ramps can be used too, but I find they don't really sound as good as a straight envelope.

It's no mini or pro-1, but I think it does a perfectly adequate snap-bass - better than I imagine most people would expect. Not sure on actual envelope attack speeds - definitely more than a few milliseconds - but it sounds fine. One benefiting factor is that the xpander (like other obie's) does not lose much bass even at high rez, so it has a good oomph regardless.


(mods, if this is listening lounge material, please move it, but I figured it was more of a discussion maker than demo)
not bad at all. Although not got gut punching bass like a Mono - certainly decent...I wonder if my OB8 is much better - the env on that arent exactly snappy either...

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Fri Feb 11, 2011 12:29 pm
by memory cords
Track by Noiseprofessor completely made with an Oberheim Xpander, showing that it can be used for fast percussive sounds:


Re: Oberheim Xpander - "slow" envelope rectification

Posted: Fri Feb 11, 2011 10:46 pm
by analogholic
Sir Ruff wrote:Having been convinced, and having convinced myself that the Xpander will always have eternally slow envelopes.
I was very concerned with the "slow" envelopes of my Matrix 12 some years ago and wondered if anything could be done to make them faster. At the time the M12 was my only analog synth.

Finally I contacted one of the chief designers of the Xpander/Matrix 12 and asked if something like the SE-1(X) "snappification" mod could be done on the XP/M12

He said the following:

"To do the job right would be very difficult because, as you noticed, the envelopes are generated by the code of the 6809 microprocessor. Short of using a faster 6809 (assuming that you could get one) and modifying the code there is not much which can be done.
The Matrix 6 and 12 were designed about 25 years ago, and microprocessors where a lot slower back then. There is still a bit of hope however. The fastest time for the envelopes is about 2 milliseconds.
This could be reduce to 1 ms by changing RX51 for the VCA (where X will be 3, 4, 5, 6 or 7 according to which of the six voice it controls on each of the two voice boards) from 18K to 9.1K.
The next fastest time is set by the microprocessor and an analog smoothing filter on the voltage control circuit (= Sample and Hold). This time is set not only by the software but also by a resistor RX14 on each of the main voice PCB for the VCA control and by RX10 for the VCF frequency control.
You may want to try reducing these resistors from their original 1 M Ohm value to let say 500K Ohm. This will reduce that time from about 7 ms to about 3.5 ms. The draw back however is that you may get more discontinuity in the shape of the modulation.
The next fastest times however will still be determined by the 6809 software and that will not change. Give it a try on one of the voice and see if that goes toward what you want.
Hope that this helps a bit."


Never got around to try this mod because later on I got some fast machines like the Pro One and Mini but still...it would be very cool if it worked.

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Sat Feb 12, 2011 1:48 am
by Sir Ruff
analogholic wrote:
Sir Ruff wrote:Having been convinced, and having convinced myself that the Xpander will always have eternally slow envelopes.
I was very concerned with the "slow" envelopes of my Matrix 12 some years ago and wondered if anything could be done to make them faster. At the time the M12 was my only analog synth.

Finally I contacted one of the chief designers of the Xpander/Matrix 12 and asked if something like the SE-1(X) "snappification" mod could be done on the XP/M12

He said the following:

"To do the job right would be very difficult because, as you noticed, the envelopes are generated by the code of the 6809 microprocessor. Short of using a faster 6809 (assuming that you could get one) and modifying the code there is not much which can be done.
The Matrix 6 and 12 were designed about 25 years ago, and microprocessors where a lot slower back then. There is still a bit of hope however. The fastest time for the envelopes is about 2 milliseconds.
This could be reduce to 1 ms by changing RX51 for the VCA (where X will be 3, 4, 5, 6 or 7 according to which of the six voice it controls on each of the two voice boards) from 18K to 9.1K.
The next fastest time is set by the microprocessor and an analog smoothing filter on the voltage control circuit (= Sample and Hold). This time is set not only by the software but also by a resistor RX14 on each of the main voice PCB for the VCA control and by RX10 for the VCF frequency control.
You may want to try reducing these resistors from their original 1 M Ohm value to let say 500K Ohm. This will reduce that time from about 7 ms to about 3.5 ms. The draw back however is that you may get more discontinuity in the shape of the modulation.
The next fastest times however will still be determined by the 6809 software and that will not change. Give it a try on one of the voice and see if that goes toward what you want.
Hope that this helps a bit."


Never got around to try this mod because later on I got some fast machines like the Pro One and Mini but still...it would be very cool if it worked.
Ah, yes - did you post this on the Xpantastic list? I'd love to find out if anyone ever tried this. If the attack time can be in fact 2ms, that is probably fast enough for me, but of course if there was no detrimental effect to the envelope shape itself, faster would be better, especially when modulations start building up! It definitely lacks that initial chord "punch" you get from similar polysynths like the pro-5.

In reality though, I was always more curious about switching up the op-amps and cleaning up the signal first (as was also mentioned on the list). That is a bigger gripe to me than the envelopes.

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Sat Feb 12, 2011 2:16 pm
by analogholic
Sir Ruff wrote: Ah, yes - did you post this on the Xpantastic list?

In reality though, I was always more curious about switching up the op-amps and cleaning up the signal first (as was also mentioned on the list). That is a bigger gripe to me than the envelopes.
Don´t remember if I posted that over there, probably did, but I do remember that I posted about changing the OP-amps to "better" ones since I discussed this with someone who actually did this to his M12 with great results

Several dudes reacted like if I wanted to kill their cat or something... :? :shock: :mrgreen: :roll:

Re: Oberheim Xpander - "slow" envelope rectification

Posted: Sat Feb 12, 2011 6:49 pm
by Sir Ruff
analogholic wrote:
Sir Ruff wrote: Ah, yes - did you post this on the Xpantastic list?

In reality though, I was always more curious about switching up the op-amps and cleaning up the signal first (as was also mentioned on the list). That is a bigger gripe to me than the envelopes.
Don´t remember if I posted that over there, probably did, but I do remember that I posted about changing the OP-amps to "better" ones since I discussed this with someone who actually did this to his M12 with great results

Several dudes reacted like if I wanted to kill their cat or something... :? :shock: :mrgreen: :roll:
cool - check your pms.