You find my answers written inline.

Best wishes
Dieter Doepfer

> So from time to time complaints about the A-137-1 pop up on
> Muffwiggler, which made me investigate the module a bit more.
> It's clear that it's nearly impossible to get the input signal
> back out unaltered, because whatever the settings the signal goes
> through 4 folding stages. But no problem, that's why mulitples
> and mixers/crossfaders are available.

I have to disagree. During workshops I demonstrate the function of the
A-137-1 in combination with an oscilloscope. And I usually start with the
(nearly) unmodified signal. It's a bit tricky to find the right adjustment
of the controls but with the aid of the scops it works.

> But I do have a question about http://www.doepfer.de/A137_block.gif
>
> It shows folding level as "a" and symmetry as "b", and the upper
> folding level as "a+b" and the lower level as "a-b". But
> shouldn't those limits be "b+a" and "b-a" Because if the level
> is at its highest the symmetry doesn't really change the output.
> If on the other hand the level is 0, there is no signal (apart
> from some noisy stuff) that comes out whatever the symmetry settings.
> So folding level defines a voltage interval, and that interval
> can be shifted up or down with the symmetry.

You are right. It's amazing that so far nobody discovered this mistake in
the sketch.

> Nice combo: VCO -> A-137-1 (with some gentle modulations) ->
> A-127+bom -> original/LP/BP/HP signals and come creative panning.

I'll have to try that out ...