The Muntz Stereo-Pak, commonly known as the 4-track cartridge,'s a magnetic tape sound recording cartridge technology. The in-car tape player that played the Stereo-Pak cartidges was called the Autostereo, but it was generally marketed under the common Stereo-Pak trade name. The Stereo-Pak cartridge was inspired by the Fidelipac 3-track tape cartridge system invented by George Eash in 1954 and used by radio broadcasters for commercials and jingles beginning in 1959. The Stereo-Pak was adapted f… (More on Stereo-pak)