| 1/00 | Two-channel systems (H04S 5/00, H04S 7/00 take precedence) |
| 3/00 | Systems employing more than two channels, e.g. quadraphonic (H04S 5/00, H04S 7/00 take precedence) |
| 3/02 | Systems employing more than two channels, e.g. quadraphonic (H04S 5/00, H04S 7/00 take precedence) 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 |
| 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 (arrangements for producing a reverberation or echo sound G10K 15/08) |
| 5/02 | Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation (arrangements for producing a reverberation or echo sound G10K 15/08) of the pseudo four-channel type, e.g. in which rear channel signals are derived from two-channel stereo signals |
| 7/00 | Indicating arrangements; Control arrangements, e.g. balance control |