Patent GB-390623-A (GB)
Title: Method of and means for producing musical tones
IPC: G10H3/06
Filed: 1932-03-11
Abstract: 390,623. Optical sound recording and reproducing apparatus. GOLDTHWAITE, D. R., 75, Varick Street, New York, U.S.A. -(Assignee of Hardy, A. C. ; 28, Upland Road, Wellesley, Massachusetts, U.S.A.) March 11, 1932, No. 7322. Convention date, March 14, 1931. [Classes 40 (ii) and 88 (ii).] Comprises a method of optically recording musical tones of predetermined quality and pitch. A primary light-controlling wave-form pattern is employed to modulate light at a frequency corresponding to each desired tonal pitch so that a record is formed on a sensitized blank of wave forms representing individual tones of different pitch which may be reproduced selectively by optical means through the employment of a keyboard control device. The tones recorded may be those of the natural or tempered scale. An apparatus suitable for recording the musical tones is illustrated by Figs. 1, 2, and 4, wherein a lamp 20, Fig. 2, is supported in a casing 24 with its filament parallel to a slot 22 in a plate 23, the light passing to the slot 22 being first passed through a diffusing screen 25. On the other side of the plate 23 the light passes through a slit 27 in a member 28, Fig. 4. Light modulations are effected by rotating a wave-form pattern 30 which varies the effective length of the line of light and so controls the amount of light which falls upon a photographic blank 84, Fig. 1. The wave form of the primary pattern may be determined arbitrarily or may be the result of mathematical or mechanical synthesis of selected partials with desired relative amplitudes. The primary pattern shown in Fig. 4 contains a single complete wavelength. The inner end of the slit 27 is adjusted by sliding the member 28 along guiding members 29 so that it is never completely uncovered by the primary pattern during rotation of the latter while the outer end of the slit 27 is adjusted to correspond with the limiting position of the maximum radius of the pattern 30. This ensures -100 per cent modulation of the light passing through the slit 27 to give a record which will produce a minimum of ground noise. The primary pattern is secured to a shaft 34 which is driven by a gear 43 and worm 46 from a shaft 47 which is rotated through gearing 49, 50 from the shafts 51 of a motor 52. The gears 49, 50. are interchangeable to vary the gear ratio, the gear 49 being provided with a hub 49a secured to the shaft 47 by a set-screw, 49b, while the gear 50 is provided with a hub 50a secured to the shaft 51 by a set-screw 50&. To vary the distance between the shafts 51, 47 when interchanging the gears 49, 50 the motor 52 is mounted on blocks 53, Fig. 2, slidable along rods 54. To reduce stray light the beam, after passage through the slit 27 and modulation by the pattern 30, is passed through a slot 59, Fig. 2, in a screen 60. The light modulations are recorded upon a rotatable photographic blank 84, Figs. 1, 5, and 7, which is secured to a holder 74 by means of V-shaped members 85. The holder 74 is mounted upon a shaft 73 'which is driven through gearing 75, 76, and 80, 8.1 by a motor 83. An image of the effective portion of the slit 27 is focused upon the photographic blank 84 by a lens device 88 which is mounted in a member 89 slidable along two rods 90. The rods 90 are connected with two standards 91 by means of blocks 92 secured to the standards 91 by screws 93, Fig. 7, and having notches in which the ends of the rods 90 are held by clamping members 95. Means are provided so that the slit 27 may be shifted to correspond with the horizontal shift of the device 88 and for this purpose the platform 31, Fig. 2, is supported on two rails 61 a pointer 62 being adapted to co-operate with a scale to determine the position of the platform. In order to record individual tones of equal loudness at differing pitch light controlling patterns may be interchanged or the distance between the light source 20 and the photographic blank may be varied. For this latter purpose the rails 61 are mounted on a carriage 64, Figs. 1 and 2. which is mounted for movement along rails 66. The whole apparatus is mounted on a table 68 supported by legs 69. , To protect the blank 84 from the influence of light other than that passing through the leiis device 88 a plate 98, Fig. 5, is provided through a slot 99 in which projects the inner end of the device 88 which is screwed into a block 89 and secured to this block 89 is a plate 100 which keeps the slot 99 covered. To afford complete protection of the blank 84 from unwanted light a casing 101, Figs. 1, 5, and 7, is provided having a slot 102 of sufficient width to accommodate the structure which slides upon the rods 90. To determine the position at which the lens device 88 is to be located in the production of tone records at individual paths on the blank 84 the member 89 is provided with a pointer 104, Figs. 5 and 7, which co-operates with a scale 105. To assist in obtaining fine adjustment with this scale a magnifying glass 106a is mounted in front of the pointer 104. Correct focusing of the device 88 is accomplished by positioning a transparent reflector 121, Fig. 1, in inclined position on an upright 125 so that the image on the blank 84 can be observed. In operation, the lens system 88 is placed in position radially of the blank 84 for recording in a desired path and the platform 31 is adjusted so that light passing through the slit 27 falls perpendicularly upon the said path on the blank 84. The gearing from the motors 52, 83 is selected so that the pattern 30 and the blank 84 rotate at the required relative speeds. The recording of further patterns of tones of different pitch on the blank 84 is accomplished by a change in the ratios between the gears 50, 49 to rotate the pattern 30 at the required differing speeds and, for exposure of each path, readjustment of the lens system 88 and of the platform 31 is effected, while a rheostat in the circuit to the light source 20 is adjusted to effect uniform density of recording. Upon completion of the recording process the blank 84 is removed from the apparatus and photographically developed to make a positive print 132, Fig. 16, which is used as the light-controlling means in the reproduction apparatus. For the preparation of primary wave-form patterns which neutralize characteristics of the playing apparatus a reproducing instrument, Fig. 19, is employed to produce a composite tone by the use of a record 132 comprising individual sine wave patterns and harmonic overtones. The record 132 is mounted on a motor-driven shaft 202 for rotation at constant speed and the recordings are scanned by a narrow stationary line of light formed by focusing on the disc 132 the image of a narrow filament 192a, of an electric lamp 190 by means of an inclined mirror 193 and a cylindrical lens 206, Fig. 20. The lens 206 is supported between two members 208 adjustably attached to plates 209 which are secured to uprights 210 in a casing 221. In order that light passing through the lens 206 may be allowed to fall on the desired lightcontrolling patterns, selectively, shutters 203, placed between the lens 206 and the record 132 are mounted on vertically reciprocable bars 204 which are held in position by guiding slots in stationary guide bars 207. The bars 204 are connected by pivots 215 with levers 216 mounted on pivots 217 and connected at their forward ends with keys 219. To maintain the shutters normally in closed position each bar 204 is connected with a helical spring 220. By depressing any one of the keys 219 the corresponding shutter will be moved to a position permitting light to scan the corresponding recording on the rotating record 132. The light after modulation by the record 132 passes to a photo-electric cell through a slit 194 in a casing 195 to cause sound variations in a loud-speaker 200. The amount of light falling on each of the record patterns is varied by the extent to which the shutters 203 are opened by depression of the keys 219, and by selection of the various partials the loud-speaker may be made to emit a tone of the desired timbre. This selection enables a curve to be drawn for the primary pattern of the tone thus empirically determined. The apparatus described is applicable readily to the recording of a natural scale record in which the successive notes of an octave are related to each other in pitch in terms of an integral series. The Specification as open to inspection under Sect. 91 comprises means for recording notes of the tempered scale where the pitch relationship of successive notes is not related to a series of integral numbers, when an adjustment of phase in the recording of the notes is necessary to avoid a disagreeable thump on reproduction. For example, if middle A is to be pitched at 440 then middle D would have to be pitched at 293À6648 and the pattern representing middle D, if rotated on the playing instrument at 1 revolution per second would require to contain this number of wave-forms so that the first wave-form recorded would be out of phase with the last partial wave-form recorded. Hence the recording is controlled to divide the total required phase shift into several smaller phase shifts. This may be effected by the apparatus of Figs. 24 and 25 (both Cancelled) which is similar to that of Figs. 1 and 2 but includes also a differential 240 introduced between the worm gear 43 and the pattern 30 to effect the required phase shifts. For this purpose the shaft 34 is divided into two parts 34a, 34b on either side of the differential. Fixedly mounted on the shaft 34a is a member 241 on an enlarged cylindrical portion 242 of which is loosely mounted a worm gear 243 carrying differential pinions 244, mounted on pivots 245, which mesh with a bevel gear 246 connected with the shaft 34a and with a bevel gear 249 connected with the shaft 34b. A spring 252 interposed between a standard 35 and a collar 253 serves to maintain the meshing of the gears of the differen