Abstract: In order to utilize standard tape players in automobiles to play compact disks, CD adapters are provided which play the CD output through the tape system of the automobile. This invention provides an in-line audio enhancement encapsulated device, manually operable by a driver to switch in the audio enhancement circuitry and adjust the audio signals produced in an efficient and safe manner so that it can be operated while a car is driven without the driver taking his eyes off the road. A bass boost circuit (24) is specifically disclosed to enhance the low frequency audio signals procuced by the automobile's audio system.