How do the FM Acoustics de-click and de-crackle functions work?

[Dialectic]

Having seen some FM Acoustics products in stores before, I am fascinated by them largely because of their high prices and strange appearance. One of their devices, however, fascinates me technically: their 223 PhonoMaster. It includes buttons to "de-click" and "de-crackle" records, purportedly entirely in the analog domain.

Do any of our technically inclined members know how these two functions might work? A demonstration of the technology is below:

 

[infinitesymphony]

I don't know, but I enjoyed reading their ad blurb in an old-timey voice.

Tremendous headroom and reserves in signal handling capability!
Astounding improvement in reproduction of vinyl treasures!
The absolute ultimate in phono linearization and preamplification!

And of course, it's all for naught if you don't use their custom tonearm cables.

 

[tmtomh]

The most well-known analogue click and pop filtering device was SAE's model 5000 Impulse Noise Reduction System. It works/worked by filtering out sounds with both of the following characteristics: (A) very fast transient and (B) out-of-phase. According to SAE (see here: http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/The SAE 5000.pdf), clicks and pops were faster transients than any musical instrument (although I wonder about electronic music!), and out-of-phase sounds that fast/sharp also were very uncommon in music.

I remember that my father briefly borrowed one from a friend in the early '80s, and it had an invert switch, allowing you to switch from hearing the musical signal, to hearing only the stuff the unit was filtering out. This allowed you to ensure you had it set conservatively enough, so it was not removing audible bits of music.

I would presume any analogue-domain click and pop reducer, even in 2018, would work on a similar principle. But I could be wrong - that happens a lot!

 

[sergeauckland]

Garrard sold a device I think it was called the 'Music Recovery Module' back in the 1970s. As I recall, it was an analogue delay line and fast switch that sensed the click and cut it out and substituted a bit of the audio before the click. Never heard it working, and it wasn't around that long.

S