Patent GB-764116-A (GB)
Title: Sound recording arrangement having means for controlling the distance between the centres of successive sound tracks
Filed: 1955-01-11
Abstract: 764,116. Sound recording apparatus. TELDEC SCHALLPLATTEN-GES. Jan. 11, 1955 [Jan. 21, 1954], No. 863/55. Class 40 (2). In a sound recording apparatus for stylus recording on disc records, the distance between adjacent sound tracks is controlled by the amplitude of the sound track to be recorded and by the amplitude of the previous recorded sound track, such that in recording the sound track at a point adjacent to an increase in amplitude of the preceding sound track a control voltage corresponding to said track is applied, for the sound track to be recorded, somewhat early to prevent the tracks running into each other, and when the recording reaches a point adjacent to a fall in amplitude of the preceding sound track, the control voltage obtained from said track applies a control voltage somewhat later to prevent the tracks running into each other. Thus as shown in Fig. 2, a first track 1 containing no modulation is unaffected, while a second track 2 containing modulation for a short distance has its mean path displaced inwardly. The following tracks 3, 4, 5, containing no modulation, are also displaced inwardly, each for increasing lengths, so that no overlap of tracks occurs. In practice, the increased length becomes a whole revolution after a few revolutions, and when this happens the control signals cancel each other and the apparatus returns to normal advance of the feed mechanism. The cutting head Ao is made to traverse the record disc by a lead screw Sp under the control of a feed motor VM. Variations in the speed of rotation of the lead screw Sp is effected by a differential gear D operated by a variable speed motor StM controlled both by the amplitude of the sound about to be recorded and by the amplitude of the sound already recorded on the previous track. Control pulses for the former of these two conditions are obtained by taking the sound to be recorded from a magnetic sound tape B by means of a head K2 which feeds the cutter head Ao. Control signals are obtained from a head K1 in advance of head K2, amplified and divided into two channels, rectified in opposite polarity to each other and the audio frequency suppressed by filters, so that differentiating members D1 and D2 supply pulses corresponding to the rise or fall in amplitude, while rectifiers G3 and G4 suppress the pulses of the undesired polarity. Modulators M1 and M2 then modulate a 50-cycle mains supply to the motor StM in accordance with the rise and fall of the sound to be recorded. Signals to produce a control voltage corresponding to the amplitude of the track already recorded are obtained by means of a memory device in the form of magnetic recording discs P1 and P2. For this purpose, pulses from rectifiers G3 and G4 are fed to modulators M3 and M4 which modulate a 185 cycles/sec. voltage, which is amplified and recorded on discs P1 and P2 by heads A1 and A2, respectively. Disc P1, which carries the pulse corresponding to the rise in amplitude, revolves at the same speed as the disc record, Fig. 2, so that a pulse picked up by head W1 is amplified and rectified, and made to modulate a 50-cycle supply to motor StM following a period of time corresponding to something less than a whole revolution from the point at which the original increase in amplitude took place. Similarly, disc P2 carries a signal corresponding to the fall in amplitude, but in this case revolves at a speed much slower than the disc record, so that the resulting control voltage affecting the motor StM occurs after the decrease in amplitude of the original signal. Automatic erazing of signals on discs P1 and P2, by heads L1 and L2, respectively, takes place, but they are immediately re-recorded by means of feedback channels U1 and U2, so that the increased spacing of the tracks continues to occur until the pulses from heads W1 and W2 occur at the same time or in overlapping relationship. When this happens, the pulses, which are of opposite polarity, cancel one another in a rectifier arrangement g, details of which are described with reference to Fig. 3.