Patent GB-412206-A (GB)
Title: Improvements in or relating to the recording and reproduction of oscillations, such for example as sound
IPC: G11B7/00
Filed: 1932-09-19
Abstract: 412,206. Discharge apparatus. WALTON, G. W., 2, Dean Street, Soho, London. Sept. 19, 1932, No. 8254. [Class 39 (i).] Apparatus for recording sound or other oscillations covering a band of frequencies comprises a glow discharge tube, and means whereby the position of the luminous discharge is varied in accordance with the frequency of applied electrical oscillations. A record can thus be produced wherein different frequencies are recorded along tracks which are displaced in relation to one another transverselv to the direction of motion of the record body. For reproducing from such a record, a light-sensitive discharge tube of special construction is used to generate oscillations, the frequency of which varies in accordance with the position of the discharge in the tube, as determined by the incidence thereon of light transmitted through the record ; the intensity of the oscillations depends upon the varying transparency of the record. In the recording apparatus shown in Fig. 1, a low-pressure discharge device is used, comprising a coil 2 of wire having rods 3, 4 arranged close to it, the coil and rods forming three electrodes which are mounted in an evacuated or gas-filled container (not shown). The electrodes are connected in circuits which include the centre-tapped secondary of a transformer 10 ; a battery 11, condensers 8, 9, 13, and chokes 12, 14 are arranged as shown. Audio-frequency currents from an amplifier 16 connected to a microphone 15 are caused by means of a device 17 to modulate high frequency oscillations from a generator 18, the output of the modulator 17 being applied to the primary of the transformer 10. The voltage of the source 11 is insufficient in itself to enable a discharge to take place between the electrodes 2 and 3 or 4, but when an oscillation of suitable frequency is applied to the transformer, 10, a discharge occurs, during one half cycle between the electrodes 2 and 3, and during the other half cycle between 2 and 4. The devices shown form two oscillatory circuits, which in each case may include any number of turns of the coil. When any particular frequency is applied to the transformer 10, the discharge between the coil and either electrode 3, 4 takes place at such a point along the length of the rod that the number of turns in the coil included in the circuit so completed is that required to adjust the circuit to resonance. Two or more frequencies occurring at the same time produce simultaneous discharges at a corresponding number of definite points along the coil 2. The number of turns in the coil is preferably so chosen that it responds to a large number of distinct stepped frequencies covering the whole acoustic range. For frequencies intermediate between any two adjacent frequencies to which the circuit can tune, the discharge occurs at a point corresponding to the nearest of these adjacent frequencies. Images of the discharges along the space between the coil and the rods 3, 4 are focused upon a moving film 22, and a record is thus obtained in which a number of parallel longitudinal lines or traces are formed, each trace representing a particular frequency in the sound being recorded, changes in intensity at that frequency being represented by variations of density in the trace. Modified forms of the discharge device are described. In one of these, instead of two rods 3, 4, adjacent to the coil 2, there is a single rod or a metal strip having an elongated aperture. The circuit used is modified accordingly. A further alternative consists in providing, instead of a rod, a second coil similar to the coil 2 arranged adjacent to it. The coil 2 may be wound in a groove on an insulating former. Fig. 7 shows still another construction of discharge device by means of which a record can be produced, on which instead of there being recorded a limited number of stepped frequencies, every frequency within a given range is recorded on its own individual track. In this case, the electrodes consist of two parallel rods 40, between which the discharge takes place. Fig. 6 shows an apparatus for reproducing sound from a record made by the above described methods. Light from a source not shown is transmitted through the moving record 221 on to an elongated aperture in an electrode 30 of a discharge device 1. The electrode 30 is adjacent to parts of a coil 2 which are coated with photo-electric material. The members 2, 30 are connected in a circuit as shown, which includes the primary winding of a transformer 10. When light falls on a particular point of the coil 2, a discharge occurs and sets up oscillations, the frequency of which depends on the number of turns included in the circuit. These oscillations are applied through the transformer 10 to a valve 31, amplified at 35, and passed to a device 36, where they modulate high frequency oscillations supplied by a generator 37. The resulting low frequency oscillations are amplified at 38, and operate a loud-speaker 39. Any of the discharge devices used for recording may, when suitably provided with photo-electric material, be used for reproduction. The discharge devices described in Specification 397,880 may also be used for carrying out the invention. Specification 403,397 also is referred to.