How Would I Nomalize Cable TV Volume Between Commercials and Programming
Typical electroacoustic systems use compressors (and variants - limiters and levelers) for exactly that - controlling the dynamic range of the signal. Those devices are used in audio production, by musicians, or e.g. to limit the modulation depth of a radio transmitter. Analogue compressors are still in wide use (I'd even say analogue compressors are more common in professional recording studios, not to mention vacuum tube ones).

What you need is basically a limiter or leveler, googling around for 'audio limiter schematics' yields a lot of results, I'd start the research from there. E.g. this one looks reasonably simple. There are also many circuits like this one, based on NE577 or NE572 or similar compander chips.

I hope that helps!