GB612163A - Improvements in or relating to methods of making sound records and to sound-recording and sound-reproducing apparatus - Google Patents

Abstract

612,163. Recording and reproducing sound. LIVY, W. H. May 14, 1946, No. 14491. [Class 40 (iv)] In a method of recording sound in which a plurality of signals of overlapping frequency ranges are recorded in a single track or groove, a sideband resulting from modulating a carrier with a first signal is mixed with a second signal and a pilot frequency which may be the carrier frequency or a harmonic or subharmonic thereof. As applied to a system of binaural recording in which the frequency range of the signals is 0-6 kc./s.,-one signal, programme 1, Fig. 1, is passed directly through an amplifier 2 to a mixer 3. The second signal, programme 2, passes through an amplifier 4 to a modulator 5, where it is mixed with a 13 kc./s. carrier from an oscillator 6, and thence through a 7-13 kc./s. filter 7, which selects the lower sideband, to the mixer 3. The mixer 3 also receives the carrier frequency directly from the oscillator 6. In the reproducing equipment, Fig. 2, a filter 12 separates the three channels, the first signal of 0-6 kc./s. then being passed directly through an amplifier 13 to a reproducer 14 while the sideband signal of 7-13 kc./s. is passed to a modulator 15. The 13 kc./s. pilot frequency is used to lock a local 13 kc./s. oscillator 16 whose output is mixed with the sideband in modulator 15 and the resultant frequency band of 0-6 kc./s. is selected in filter 17 and passed to the second reproducer. The locking of the local oscillator 16 by the recorded carrier frequency ensures that there shall be no discrepancy in frequency between the two speech signals if speed variations occur in either the recording or reproducing turntables.