| 摘要 |
PURPOSE:To ensure the discrimination among stereophonic, double sound and monaural modes in a reproduction time, by inserting a pilot signal of an optional frequency at the outside of an audible band selectively in response to at least stereophonic, double sound and monaural modes of an audio signal. CONSTITUTION:A signal P sent from a pilot signal oscillator 32 of 25kHz is supplied to a switch circuit 33 and switched among contacts of modes of stereophony S, double sound B and monaural M to be supplied in common to adder circuits 13L and 13R through diodes 34L and 34R, respectively. At the same time, the signal supplied from the contact B is fed to the circuit 13L. The pilot signal P is selectively superposed on the spectrum of an audio signal which undergoes FM modulation in the stereophonic, double sound and monaural modes at the outside of audible bands (0-20kHz), i.e., 25kHz and in response to the stereophonic and double sound modes. When control signals SB of double sounds are detected in a reproduction time, just one of these two signals is extracted at the output side. Furthermore, a signal obtained by adding both signals is extracted at the output side when a signal SM is detected. |
