GB1410772A - Audio frequency signal changing circuits - Google Patents

Abstract

1410772 Stereophonic systems NIPPON COLUMBIA KK 8 Aug 1972 [11 Aug 1971 30 Nov 1971 14 April 1972 25 May 1972] 17062/75 Headings,H4R and H4J An audio frequency signal charging circuit substantially cancels from. a pair of stereophonically related first audio frequency input signals respective substantially identical components of the two signals which are of the same phase and level and which occupy a band within the first signals. The remaining signals are mixed with a second audio frequency input signal which has a frequency range occupying at least part of the band. Stereophonically related input signals 1L, 1R (Fig. 1) are applied to phase splitters 47L, 47R to provide outputs of opposite phase. Outputs (-) of one phase from the phase splitters 47L and 47R are directly applied to adders 48L and 48R and outputs (+) of opposite phase are also fed to the adders 48R and 48L through respective phase shifters 49L and 49R having a voice frequency band width. When a microphone 6 is operated and switch in by a switch (S), Fig. 4 (not shown), centrally located vocal sounds in the stereophonic image are removed from signals 1L, 1R by virtue of phase shifters 49L, 49R while voice frequency signals from the microphone 6 are superimposed on the remainder of the signals 1L, 1R. In an alternative arrangement, switching is performed by a switching circuit in each channel, comprising a F.E.T. 53L, 53R (Fig. 5), the gate of which is supplied with a drive signal when the microphone 6 is used. The output of microphone 6 is amplified by an amplifier 7, envelope detected by a detector 21e, shaped by a waveform shaping circuit 22e and applied to each F.E.T. gate. The circuit operates such that when the microphone 6 is not in use the resistance between the source and drain of each F.E.T. is low and the signals from phase shifters 49L, 49R are cut off. When a voice frequency signal is applied to the microphone, a corresponding operating signal is applied to the gate of each F.E.T. to render the phase shifters 49L, 49R operative. Only a centrally located sound signal in the voice frequency range is removed or suppressed from the stereophonically related signals 1L, 1R when the phase shifters 49L, 49R are operative.