A signal processing device whose operating parameters change as a reaction to the program content. For example, a compressor or expander. See Static Signal Processing Device.
"I received CD's and MP3 CD's yesterday for the 3 reel-to-reel tapes I sent in. These were pretty old tapes (one around 33 years old) that had not been on a player since the 1980's when my reel-to-reel recorder was stolen and never replaced. One of them, in particular, contained unreplaceable studio performance tracks from a record album I had ..."