Patent GB-818585-A (GB)
Title: Improvements in or relating to sound recording systems
Inventor: TERRY MICHAEL TREACHER
IPC: G11B3/00
Filed: 1955-10-25
Abstract: 818,585. Recording sound. ELECTRIC & MUSICAL INDUSTRIES Ltd. Oct. 22, 1956 [Oct. 25, 1955], No. 30449/55. Class 40 (2). Means for recording a laterally modulated sound groove on a disc record, in which the groove pitch is varied in accordance with the , amplitude of'the signals, comprises means for deriving a first set of signals advanced in time relation to a second set of similar signals, applying said first signals sequentially to a plurality of control channels each of which controls the groove spacing for part only of each revolution of the record disc, and utilizing the second set of signals for recording the sound on the record. In the embodiment described, the first and second signals are obtained from a magnetic tape record 1 by-means of magnetic heads 4, 5 arranged inspaced relationship, the head 5 producing recording signals and head 4 providing signals in advanced time relationship to - the head 5, corresponding to a quarter revolution of a record disc 2, to control the speed of traverse of the recording cutter head 8 across the record disc 2. A motor 10 rotating at constant speed causes the cutter head 8 to be traversed by a lead screw 9 the speed of which can be varied through a differential gear 12 by a motor 40 operated in response to signals derived from the head 4. In the present embodiment, four channels (only one of which, comprising the parts 26, 27, 28, 29, being shown) are employed to control the motor 40, each control channel corresponding to a sector 22, 23, 24 or 25 of a rotary switch rotating with the record disc 2. Slip rings 43, 34, 35 associated with the channel parts 26, 27, 28, 29 also rotate with the record disc. Similar switches (not shown) are associated with the three channels previously mentioned but not shown. When signals first reach head 4 at the commencement of a recording, and the sliding contact 13 just reaches, say, contact 22, the signals are fed to a rectifier 26 which has a standing bias and therefore only passes to a temporary store 27 signals with a greater amplitude than can be accommodated by normal groove spacing. Should the signals be heavier than normal, at the end of a quarter revolution when sliding contact 15 connects the ring 43, having a fixed potential, to contact 42 a switch 28 is actuated and transfers information from store 27 to a cumulative store 29 from whence it is fed to a contact 30 of switch 19 and subsequently to the selector 36 via sliding contact 17 to an amplifier 37, the out, put of which energizes motor 40 to impart additional rotation to lead screw 9 to space the more heavily modulated groove from the previous unmodulated groove. In order to allow for the amplitude of the record groove both sides of its mean, it is necessary to provide a similar increased spacing at the same part of the next revolution. For this purpose a contact 44 of switch 16 is connected to switch 28 whereby the latter is actuated a second time by contact 15 after the recording in second quadrant but before that quadrant is reached in the second revolution. After the second actuation of switch 28, the store 27 is discharged via contact 45 so that temporary store 27 is in a condition to receive afresh charge from rectifier 26. The other channels connected to contacts 23, 24, 25 of switch ring 14 operate in sequence in a similar manner, through the other quadrants, switch 16 being provided with three further contacts per channel and each set successively dispaced 90 degrees. Contact 18 is provided on switch 19 to provide a second input to selector 36 whereby only the greater of the two inputs is passed on to amplifier 37.