What is Pre-FM

[ffooky]

I've just downloaded a White Stripes show from DIME which is described as "SBD->DAT->Pre-FM" but the frequency and spectral analyses seem to me indistinguishable from what I'd expect from an FM source: 15 KHz cut-off, some "noise" above that and a 19KHz pilot tone.

What exactly is Pre-FM and what characterises it in terms of analyses ?

[oldbrokentapes]

Well what you've downloaded is falsely labelled by the sound of it. "Pre-FM" refers to where a direct copy of a broadcast show "leaks" directly from the radio station master, so it doesn't suffer from any of the FM features you describe. A true pre-FM source should have the full spectral range that you'd expect on a radio station DAT master.