1
J P Fricke, Ulrich R Muller: System for reproducing sound information. Flynn & Frishauf, December 6, 1977: US04061874 (39 worldwide citation)

In an environment of acoustic noise, such as a car radio playing in traffic or engine noise, both the volume (AGC) and dynamic range (Compression) of the audio amplifier are controlled by a local ambient acoustic noise sensor, such that gain is increased and dynamic range decreased simultaneously wi ...


2
Jobst P Fricke, Ulrich R Muller: Dynamic volume expander varying as a function of ambient noise level. Frishauf Holtz Goodman & Woodward, April 26, 1983: US04381488 (18 worldwide citation)

To provide for response of audio reproduction equipment with the full dynamic level range, for example of music, intended by a composer, although radio signals transmitted have been compressed to reduce the signal-noise level, an expander circuit (20a, 20b, 20c) is activated based on ambient noise l ...