US2158268A - Voice and music mixer for use in sound recording - Google Patents

Description

J. o. BAKER 2,158,268

VOICE AND MUSIC MIXER FOR USE IN SOUND RECORDING 7 May 16, 1939.

Filed April 50, 1936 (Itfomeg Patented May 16, 1939 UNITED STATES PATENT OFFICE VOICE AND MUSIC MIXER FOR USE IN SOUND RECORDING of Delaware Application April 30, 1936, Serial No. 77,11

3 Claims.

This invention relates to the simultaneous recording of speech and music or other acoustical effects and pertains more particularly to a method of and apparatus for recording speech together 5 with either music or other effects in such a manner that the speech is not obscured by the accompanying sound.

In the producing of sound records and particularly sound records to accompany motion pictures it is customary on occasion to prepare a record of music or sound effects and to later add other record by re-recording speech at the appropriate places. In doing this it is necessary to have the music at a sufiiciently high level to be satisfactorily audible when there is no speech. It is, ac-

cordingly, necessary to have the speech either harsh or extremely loud or to decrease the volume of the music when speech occurs.

It is pointed out in Mueller Patent No. 1,888,467

0 that in prior practice such effects have been performed manually and the said patent discloses the use of the special input currents to control the gain of the music or effects amplifier reducing the gain of the amplifier when speech occurs in 25 a predetermined manner and again increasing it at the end of the speech. Such apparatus, of course, operates with sufficient rapidity to avoid either blanketing speech by the music or relatively silent intervals either of which may occa- 30 sionally occur with manual control. As distinguished from the customary manual method and from the method disclosed by the aforesaid Mueller patent, I propose to control directly the sound reproducing device, which introduces the music or 35 sound effects to the recorder and to accomplish this control from the speech amplifier. I prefer, in the performance of my invention, to use the photoelectric type of sound reproducer and to accomplish the volume control by controlling the 40 intensity of the beam of light which is directed to the film sound record.

One object of my invention is to provide a novel recording apparatus for adding speech to a music or effects record.

45 Another object of my invention is to provide a novel method of re-recording sound.

Another object of my invention is to provide a photo-electric film phonograph with automatic volume control.

50 Another object of my invention is to provide a photo-electric film phonograph in which the volume is controlled by an independent source of sound.

Other and ancillary objects of my invention will 55 be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which the single figure is a schematic diagram of the amplifier circuits I prefer to use and a sectional diagram of the essential elements of the film 5 phonograph shown in proper relation to the amplifiers.

The apparatus includes a sound recorder which is diagrammatically indicated at Hi. This recorder is preferably of the variable area electro- 10 photographic type but may be any other known type of sound recorder capable of electrical actuation. The main recording amplifier is indicated at II. This amplifier is of a customary type including thermionic tubes with appropriate con- 16 necting circuits and the usual appurtenances thereto. I prefer to use an amplifier embodying both resistance and transformer coupling in order to secure any desired frequency characteristics but this is not essential. 20

Current is fed to the amplifier H from the mixer l2 which serves to determine the input level to the amplifier by the potentiometer i3 and to determine the respective input levels from the film phonograph and the speech input by the potentiometers l4 and Hi. It is not essential that single-resistor potentiometers, as shown, be used as these merely schematically indicate appropriate volume control resistances which may be simple potentiometers or potentiometric devices of T- pad or H-pad type or the equivalent. The speech input device is indicated at l6 as a microphone. It will be apparent, however, that this may be any desired type of speech input or sound effect input and it may be a phonograph of any desired type. The output from the speech input device is fed to the speech amplifier I! which, like the amplifier ll, may be any desired type of thermionic amplifier and, as pointed out above, the output from the amplifier I! is fed through the mixer I2 and the amplifier H to the recorder ID. The music input amplifier is indicated at H! and the input for this is supplied by the photocell lB. The photocell I9 is supplied with light modulated by the film sound record 29 which in turn is illuminated by the exciter lamp 2|, the light from which is focused on the film in the form of a fine line by the optical system 22 including the condenser lens 23, slit 24 and the objective In order to control the acoustic level of the music introduced I divert a portion of the output from the amplifier I! through the leads 26 to the amplifier generally indicated at 21. This amplifier includes the thermionic amplifier tube 28 provided with appropriate coupling circuits. The output from the amplifier 28 is fed through a transformer 29 to the rectifier circuit 30 which is a bridge circuit including four rectifiers as indicated. It will be apparent that this arrangement provides the rectifier circuit 30 with audio frequency currents and that this rectifier changes these audio frequency currents into a direct current varying in accordance with the amplitude or volume of the speech input. In other words the output of the rectifier provides what is generally referred to as an envelope current varying in accordance with the input to the amplifier II.

It will be apparent that for the purpose of this inventionit is necessary to decrease the output from the amplifier l8 in accordance with the increase of output from the rectifier 30. In order to do this I provide a shutter 3| which is movable about the pivot 32 by the action of the magnet 33. This shutter is located between the filament 34 of the exciter lamp 2| and the slit member 24. As indicated in the drawing the filament 34 is preferably of the coil type which has a finite diameter. When the output from the rectifier 30 to the magnet 33 increases, the magnet draws the member 35 downward against the action of the spring 36, thereby raising the shutter 3|. As the shutter 3| rises it masks more or less of the Width of the coil filament 34 from the slit 24, thereby causing the slit 24 to pass from full illumination into the gradually increasing shadow of the shutter 3| which is referred to as the penumbra and at maximum excitation of the magnet 33 and corresponding maximum elevation of the shutter 3| to approach the total darkness which is referred to as the umbra. It will be apparent that by properly locating the shutter and magnet in relation to the filament 34 I may adjust the device to provide any desired degree of maximum or minimum shade or both; and that I may adjust the rate of change of shade and correspondingly the rate of change of music input in any ratio to the speech input that I- desire by adjusting the sensitivity of the amplifier 2'|,-this change of sensitivity may be accomplished in any desired manner although the most convenient way is to use a variable mu tube at 28 and to adjust the grid bias thereon by varying the value of the resistor 31 or by using battery bias instead of the biasing resistor 31 and varying the value thereof.

Having now described my invention, I claim:

1. A film phonograph comprising a light source, an optical system for directing light from said source upon a film sound record, photoelectric means in cooperative relation to the said optical system, a volume control comprising an electrically actuated shutter between said light source and said optical system, and amplifying means and rectifying means controlling said shutter inversely in accordance with sound from another source.

2. Apparatus of the class described comprising sound reproducing means, amplifying means, mixing means and recording means connected in sequence, a second sound reproducing means and amplifying means connected through said mixing means to said recording means, and means connecting the second amplifying means with a first sound reproducing means for controlling the volume of sound produced thereby, whereby the volume of sound recorded from said first sound reproducing means may be varied while maintaining the amplification ratio of said first amplifier constant.

3. Record re-recording apparatus including a photoelectric film phonograph, including means for directing a beam of light through a sound record to a photoelectric cell, a second source of electrical impulses corresponding to sound waves, and means for controlling the intensity of said beam of light in accordance with the amplitude of the sounds from the second source.

JUDD O. BAKER.

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