The Phillips patent on the compact cassette demanded that all recorders must be compatible with all cassette players ... e.g. 1 7/8 ips tape speed, and 2 (mono) or 4 (stereo) tracks recorded on two sides of the tape (and physically flipped to play the other side). That ruled out quadraphonic decks (which required all 4 tracks to be recorded in the same direction), or decks that ran at 3 3/4 ips. Even dbx noise reduction was an issue, since playback without dbx decoding wasn't a pleasant experience. Keep in mind that Phillips never intended the cassette tape to be a high fidelity medium, only for dictation machines. Once the patent ran out though, all bets were off and multi-track and two-speed decks started to enter the marketplace. Sadly, it was too late for quad.