"Abstimmbarer anzeigeverstärker"...anyone heard of

[Sw-Michael]

Not strictly a VST questions...

I'm doing some research on Karlheinz Stockhausen. An important device in his early sound construction was the "Abstimmbarer anzeigeverstärker". Googling hasn't lead me any further than that it is a frequency tunable amplifier with variable feedback and it is said to work "as a special kind of band pass filter".

Typically he tuned it in a lower frequency range, like 50-100Hz. Since that wouldn't lead to very exciting sounds if it was similar to an ordinary band pass filter, I'm guessing it also amplifies multiple overtones.

Can anyone shed some light on this elusive device?

[helium]

Well, all I find out is that it's a bandpass filter wich can have a very thin band so it starts to oscilate on it's own.

[Sw-Michael]

Typically he followed the device with a "terzfilter" which is an ordinary band pass filter with a fixed ratio between upper and lower cutoff. But if you have the anzeigverstärker tuned at eg 65 Hz followed by the terzfilter at around 1000 Hz you won't get any sound at all, unless the anzeigferstärker generates a lot of overtones.

[shamann]

Best I can tell, here's a picture of it:



Picture caption called it an "Adjustable detector amplifier (feedback filter, type UBM)" in English, where UBM I think means Universal Background Model. Found here on a production outline for Hymnen. If you haven't seen it before, check out that site, great info and photos of old gear.

I found a bit here, where Stockhausen describes "a feedback filter whose width could be continuously changed." So I'm guessing it's similar to a one-band peak filter/parametric EQ.

[Sw-Michael]

Thanks!

I was also into the variable feedback bandpass filter explanation. But in the Kontakte dokumentation, Stockhausen has even documented what device chains and settings he uses for single sounds (!) and I can't really get it to make sense.

[shamann]

I love that picture. Looks less designed for music and more designed for a war bunker, which most likely it actually was.