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.

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.

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