[guygee]

Sorry I cannot post any audio samples for the original show that started this thread as they are not mine to post. But in general all this talk of stray signals being picked up by the cables or recording equipment does not completely explain the definite bias I have seen for a small signature ~15.5Khz-16KHz in some supposed pre-fm and many fm recordings, unless it is truly interference from a TV signal either at the source or the receiver. For FM recordings I could show many examples (by no means ubiquitous, but often enough to distinguish from a case like Five's example above).

Perhaps the fact that both FM and TV transmitting stations are often located closely together in preferential locations (Empire State Building, Mt. Wilson, etc.) may contribute? I've seen this little "signature" in some old FM jazz recordings dating back into the 1950's, so I doubt the complete explanation is people recording FM while watching TV, but it may be a combination of several factors that can come into play during recording, during transmission, and/or during reception and re-recording.

I am still holding this topic open as a question mark, but the "TV signal interference" is the (IMHO) "better-than-SWAG" hypothesis that I am taking out of this discussion until/unless a better explanation comes along.

I love this forum for all of the knowledgeable people who care enough to reply. Thanks to you all.