This class covers electrical communication systems with propagation paths employing light (optical communication), infra-red, ultrasonic, sonic, or infrasonic waves.
of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other [3]
H04S 5/00
Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation [3]
H04S 5/02
·
of the pseudo four-channel type, e.g. in which rear channel signals are derived from two-channel stereo signals [3]
H04S 7/00
Indicating arrangements; Control arrangements, e.g. balance control [3]