Sound recording apparatus; sound transmitting apparatus; sound reproduction apparatus; sound processing apparatus; sound mixing apparatus; video recorders; camcorders; electric and electronic effects units for musical instruments; digital sound processors; analogue sound modifiers; audio interfaces; audio and video receivers; audio equalizers; data processing apparatus; transponders; megaphones; loudspeakers; monitoring apparatus and instruments; headphones; sound amplifiers; amplifiers for musical instruments; audio mixers; audio mixing consoles; stage lighting regulators; microphones; acoustic couplers