Remember audio amplifiers and loudspeakers have been with us for over 100 years. ADC was just recent phenomenon that wasn't there even in the 1970s. So there must be plenty of analog narrow single frequency filters in museum? Which audio museum has that?
So the official word to use is "analog narrow single frequency filters" or analog notch filters? But the latter term would be confusing as this would mix it up with the notch filters. What exact words do you suggest?
We have a renaissance now of vinyl, and many people still own vacuum tubes amplifiers as they sound better. So I want to get hold of this analogy filter technology. How to find it at ebay? I use spectrum analyzers for vocal analysis of singers and music. And I just want to try pure analog frequency analyzers just to see if I can hear better just like in vacuum tubes where music is said to be richer.