The Official Sequential/DSI Forum

Pulse width tolerance seems different on different voices

Pulse width tolerance seems different on different voices
« on: January 20, 2021, 06:33:14 PM »
Hi all! 

Sorry if this has been posted before, but this is perplexing me a bit.

I've just noticed that the square voices sound different as I play a single note and cycle through the voice cards.  Vintage knob is set to 0 and I can't tell if I had this issue before the OS update or not.

VCO 1

Square - Two voices sound like pure square waves, but four of them do not sound pure until I adjust the pulse width slightly, then four sound like a pure square wave and the other two now do not. 

It *is* possible to get all 6 voices sounding like a square wave by adjusting the pulse width by a tiny amount, but is incredibly twitchy getting this to work.  What should the tolerance be?  The tuning appears to be OK.

Saw - Seems fine.  Tuning is fine.

VCO 2

Square - Same issue as VCO 1, but even more so.  Even more difficult getting a consistent pure square sound out of each voice with the same pulse width setting.

One voice sticks out when the oscillator is set to triangle, like it's more towards the saw setting than the others.

Is there a way of adjusting the tolerance of the Pulse width and oscillator knob on a per card basis, or will it need new cards?  Or does this behavior sound like it's within acceptable tolerance?

Thanks!



Re: Pulse width tolerance seems different on different voices
« Reply #1 on: January 30, 2021, 10:36:08 AM »
The real question should be is it affecting the musicality to a noticeable/perceptible degree?

Re: Pulse width tolerance seems different on different voices
« Reply #2 on: January 30, 2021, 11:13:56 AM »
If you need an absolute and perfect square wave oscillator, you could use the Sub Osc (with VCO1 pitched one octave higher, but with its level set to 0) as a VCO?

Otherwise, this is an analog synth, with very slight "miscalibration" variations, dictated by Tom Oberheim himself when he and Dave Smith designed the OB6. Which makes it alive and not digitally sterile.
Minimoog D (vintage), OB6 (Desktop), Oberheim Matrix-6 (MIDI Controller), Prophet REV2-16, DeepMind 12, VC340