US1623756A

US1623756A - Recording and reproducing of sounds

Info

Publication number: US1623756A
Application number: US711033A
Authority: US
Inventors: Charles F Sacia
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1924-05-05
Filing date: 1924-05-05
Publication date: 1927-04-05
Anticipated expiration: 1944-04-05

Description

April 5, 1927.

C. F. SACIA RECORDING AND REPRODUGING on souuvs Filed May 5, 1924 fly] FQPQQ cocoon Phoio el. Cell GridPofential 0 Confrol VoltagaL I Paengea Apr. 5, 1927.

UNITED STATES PATENT OFFICE,

CHARLES I. SACIA, OF NEW YORK, N. Y., ASSIGNOR '10 WESTERN ELECTRIC COMPANY INCORPORATED, 01' NEW YORK, N. Y., A CORPORATION 01 NEW YORK.

RECORDING AND REPRODUGING OI SOUNDS.

This invention relates to sound recording and reproducing systems, and particularly to methods of and means for recording and reproducing sounds having a wide range of intensities.

As is well known, there is a fairly definite limit to the range of intensity of spoken or musical sounds that can be satisfactorily recorded by present known means, such as the phonograph record and the photographic. film. This .is due inpart at least, to overload distortion at large amplitudes and to the suppression of important high frequency components by the insufiicient resolving power of the recording material, the phonograph disc, the photographic film, etc. It is desirableto greatly increase the inten-' sity range of recording, for example, in the case of talking moving pictures and the good quality reproduction of orchestra Il'lllSlC.

An object of this invention is to provide a method of and means for accurately recording sounds having a wide-range of amplitudes using resent known means.

A further obJect is to provide a. method.

of and means for accurately reproducing the original sounds from thefrlfecords obtained in such a recording process.';

The invention provides for making two records of the sounds, (a)*.'a record of the sound reduced to an arbitrary or artificial standard intensity irrespective of the actual intensity of the sounditself, and '(b) a record of the intensity of the sound. Furthermore, it provides that in "the production of the (alrecord the instantaneous am litudes of the recorded sound; Variations s all be controlled by the same energy which produces the (6) record. In the reproduction, the two records are utilized. the output of the (a) record being controlled by the output of the (6) record in such a way that variations in intensity, which were removed in the production of the (a) record, are

reinserted and an exact reproduction of the original sounds both in wave form and in intensity is obtained.

These methods. 'appl most readily to elec trical means of recor ing and reproducing sounds and \vill'beillustrated in that way, although they are not necessarily limited to such means. -A recording circuit comprising a telephone transmitter, an amphfier, a vacuum tube rectifier and a low pass filter may be used for transforming the sound energy into electrical energy and forfurnishing the current for o crating a suitable recording device for ma ing the (6) record. The variations in the rectified current output of this circuit wil be directly pro or- .tional to the variations in the intensity 0 the sounds received by the transmitter and the (6) record will, therefore, bean accuraterecord of these variations in intensity. In obtaining the (a) record, that is, a record of the sound reduced to a standard constant intensity, the invention makes use of the fact that the amplification of a. thermionic amplifier of the audion type depends upon the voltage impressed upon the grid or in put circuit. A recording circuit comprising a telephone transmitter, an amplification regulator and an amplifier in connection with a suitable recording device is used for making the (a) record. The telephone transmitter used in the (a) circuit may be the same one used in the (b). circuit, or a separate transmitter may be used for each circuit as shown in the accompanying drawing. The output of the low pass,- filter 'in the auxiliary recording circuit used for making the (6) record, described above, is used for furnishing low frequency, rectified voltage to regulate the potential on the grid of regulator, the regulation, however, being .the

reverse of that ,in the recording system. The output of the (a) record is also impressed on the input circuit of the "amplification regulator. Then, the variations in represente representation of the amplification regulator used in the recording and reproducing circuits shown in Figs. 1 and 4, respectively. Fig. 3 shows the characteristic curves of an electron discharge device for illustrating the operation of the amplification regulator shown in Fig. 2. 'Fig. 4 is a diagrammatic representation of a sound reproducing arrangement embodying the invention. Fig.

- 5'shows a section of film indicating one form of sound record obtained using the arrangement shown in Fig. 1.

Referrin to Fig. 1, a source of variations, by the telephone transmitter 1 is connected to the input circuit of the amplification regulator 3, the output circuit of which is connected to the input circuit of the amplifier 4. The output circuit of the amplifier 4 is connected to the movable wires of alight valve 5 arranged to vary the quantity of light from'a source 6 falling on a film 7, in accordance with the variations of current received. Similarly, the source of signals, represented by the transmitter 8 is connected to the input circuit of the amplifier 9, the output circuit of which is connected to the input circuit of a vacuum .tube rectifier 10. The output circuit of the rectifier 10 .is connected to the input circuit of a low pass filter L'PF, the output circuit of which is connectedto the movable wires of a light valve 11 arranged to vary the quantity of light from a source 12 falling on the film 7, in accordance with variations in the current received. The output circuit of the low pass filter LPF is also connected to the control terminals of the amplification regulator 3.

The transmitters 1 and 8 are preferably of the t e described in the article entitled The ensitivity and Precision of the Electrostatic Transmitter for Measuring Sound Intensity, by E. C. Wente, published in the Physical Review for May, 1922, and their circuits are preferably as described in that article. The amplification regulator 3 is described later.

uum tube type. .The rectifier 10 may also be of the three electrode vacuum tube type,

The amplifiers 4 and 9 maybe of the well known-three-electrode vac-' the grid of which is maintained predominantly negative. The recorders 5 and 11 may be any suitabletype but are preferably of the type shown in Fig. 1 and illustrated and described in detail in the copending application of E. C. \Vente, Serial No. 635,886, filed May 1, 1923, which type is adapted for making sound records on photographic films. The low pass filter LPF may be of the type disclosed in U. S. Patent to G. A. Campbell, No.-1,227,113, dated May 22, 1917, and preferably designed to pass frequencies ranging from zero to the neighborhood of 10 cycles, or in some cases up to 50 cycles depending on the nature of the sound to be recorded.

The circuit and apparatus having been generally described, its exact nature will be more clearly understood by a detailed description of its operation. Sound variations received by the transmitter 1 are supplied to the input circuit of an amplification regulator 3, repeated in its output circuit, and amplified by the amplifier 4. The corresponding variations in current in the output circuit of the amplifier 4 are transmitted through the conductors of the light waves 5 causing variations in the width of the slot in the valve 5 corresponding to the variations in current received, thereby va-. rying the quantity of light from the source 6 transmitted through the slot. This light is focused on a continuously moving film 7 to produce a series of striations of varying intensity, corresponding to thesound variations, constituting the (a) record of the sounds to be recorded. In a similar manner, sound variations received by the transmitter 8 are supplied to the input circuit of an amplifier 9 and repeated in its output circuit. The variations in the outputlcircuit of the amplifier 9 are supplied to the input circuit of the rectifier 10, and the corresponding rectified variations in its output circuit are transmitted through the low pass filter LPF to the light valve 11, which in the same manner as described for light valve 5, causes the (6) record to be recorded on the film. The variations recorded on this record will be directly proportional to the variations in intensity of the sounds received by the transmitter 8. The output of the low pass filter LPF besides furnishing the current for operating the recorder 11 for making the (6) record is connected to the input circuit of the amplification regulator 3 in the circuitfor making the (a) record to furnish a slowly varying rectified voltage to the grid of the regulator to control its amplification. The amplification regulator, which 1 is described in detail below, operates in the recording system 'so'as to cause weak ami 'plifications of loud sounds and strong amplificationsof faint sounds. "Thus, the (b) record will be a-re'cordof the variations in intensity of the sounds receiv'ed-b y the trans-- mitter, while the (a) record will be a record of-the sounds reduced to'aconstint standard intensity. The two records may be on the same unit (possibly even on the same track); as illustrated in Fig. 1, or they may" be made on different units suitably synchronized. The former method which is the preferred method, has been specifically illustrated.

It may be necessary to cause operation of A the circuit usedfor making the (a) record is K times the frequency, the time lag is second.

fThe theory covering t e operation of the regulator can be best shown by consideration of the characteristic curves 0 a vacuum tube amplifier as shown in Fig. 3. Suppose a vacuum tube is connected to a low impedance output the amplitude of the superimposed alternating current waves being small .enough not to be distorted by this impedance relation, then its characteristic curves will be like those shown in Fig. 3. Theupper curve gives the relation between the internal re-- sistan'ce of the tube and the grid potential,

and the lower curve the relation between the amplification of thetube and the grid potentia The amplification is where a is the amplification constant of the tube, R is the external resistance, and R is the internal resistance of the tube. As shown by the curves, the amplification is approximately inversel pro ortional to the internal resistance of t e tu e, and over a considerable range can be made to be proportional to the grid voltage. Therefore, a negative voltage applied to the grid willcause a decrease in the plate current, an increase in the internal resistance, and hence a decrease in the amplification in proportion to the applied grid potential within the range indicated.

Referring now to the circuit of the ampli: fication re lator shown in Fig. 2, 13' is a vacuum tu amplifying device comprising a cathode 14, anode'15 and a control electrode 16. The cathode 14 is heated to 'incandescence by battery 17, and is maintained positive with respect to control electrode 16 battery 18.- The input circuit of the will now amplifier 13'inclu'de's the cathode 14, resistance 19,) esistance 20, battery 21, and the control electrode 16. The output circuit of the am lifier 13 includes the anode 15, the adjusta le resistance 22, the battery 18, and the cathode 14. The adjustable resistance 22 may be used for varying the external resistance in the output circuit.

In operation in the circuit as shown in Fig. 1 sound variations from the transmitter 1 are impressed on the input circuit across the resistance 20 and are repeated in the output circuit of the tube. he output of the low pass filter LPF, is connected across the resistance 19 to furnish the varyingrectified control voltage for varying the grid 1 potential. The leads from the low pass filter LPF are so connected, that an increase in the drop across the resistance 19, caused by an increase in the current received from the low pass filter LPF, will cause an increase in the negative voltage applied to the grid, an increase in the internal resistance of .the tube, and therefore a decrease in the amplification. However, as mentioned above, when the. amplication regulator is used in the reproducing circuit shown in Fig. 4, the leads from the amplifier 32 are so connected across the resistance 19 that an increase in the drop across the resistance 19, caused by an increase in the amplified current received in the reproduction of the (1)) record, will cause a decrease in the negative voltage applied to the grid, 9. decrease in.

the internal resistance of the tube, and, therefore, an increase in the amplification. When the amplification regulator is used in the recording system-of Fig. 1, the direct current component of its output current is prevented from passing to the amplifier 4, by the condenser 23. Likewise, when the regulator is used in the reproducing circuit of Fig. 4, the direct current component of its output current is prevented, from passing to the amplifier 34 by the condenser 23. Thus, in the recording system shown in Fig. 1, loud sounds received .in the transmitter which cause weak amplification and faint sounds strong amplification, while in the reproducing system shown in Fig. 4, the regulating action is reversed This regulating device may be made part of the first stage of the amplifier, as shown in Fig. 2, or maybe used as a separate unit in conjunction with an amplifier. The regulation can be applied to more than one step if desired, hence a tamed.

The re roducing system shown in Fig. 4 described. The film 24 is shown positioned between a light source 25 and the

photoelectric cells

26 and 27. This film,

very large range of amplification can be obshown in more detail in Fig. 5, is a positive made from a negative film produced in the recording process, and contains on its surin theopaque screen 29, and transparencies in the film 24, are focused by lenses 3'0 and 31 upon the

photoelectric cells

26 and 27, respectively. The photoelectric cell 26 is connected to the input circuit of the amplification regulator 32. The photoelectric cell 27 is connected to the input circuit of an amplifier 33, the output circuit of which is also connected to the input circuit of the amplification regulator 32. The output circuit of the amplification regulator 32 is connected to the input circuit of another ampli:

fier 34, the output circuit of which is connected to the sound reproducer 35. The amplifiers 33 and 34 and the amplification regulator 32 are similar to the corresponding apparatus described in connection with Figs. 1 and 2. The sound reproducer 35-1nay be of any suitable type for example, such as a. telephone receiveror loud speaker.

The circuit and apparatus used in Fig. 4 having been generally described, its enactnature will be more clearly understood by a detailed description of its operation. The light rays from the source 25 transmitted through the lens28 apertures in the opaque screen 29, and the transparency of the film 24, and focused on the photoelectric cell 26, cause the current from the battery 36 How- :ing through the photoelectric cell 26 to vary in accordance with the striations correspnd- F ing to the (a) record on the film 24,which variations are impressed upon the input circuit of the amplification regulator 32.

Similarly, the light rays from the source 25 transmitted through the lens 28, other apertures in the opaque screen-129, and the transparency of the film 24, and focused on the photoelectric cell 27 by the lenses 30 and 31 cause the current from the battery 37 flowing through photoelectric cell 27 to vary in accordance with the striations corresponding to the (b) record on the film 24. These variations are impressed upon the input circuit of amplifier 33, repeated in its output circuit, and supplied to the grid of the amplification regulator 32, ;varying the amplification in accordance with the variations in the (1)) record. The operation of the amplification regulator is the reverse of that obtained in the recording, as explained above in connection with the description of the operation of the amplification regulator shown in Fig. 3, the variations in intensity, which were removed in the product-ion of the (a) "record in the recording system, being reinserted. The variations the output circuit of the amplification regulator 32 are amplified by the amplifier 34 and supplied to the sound reproducer 35, which reproduces the original sounds recorded over a wide range.

or intensity.

tric cell 26 and the amplification regulator 32 to have a slight phase lead over the 0 eration of the circuit including the photoe ectric cell.27 and the amplifier 33 to insure due action of the amplification regulator. This time lag may be produced by mechanical adjustment, by means of. an electrical network, or by any system which possesses a hase lag proportional to the frequency. The systems tabove illustrated and described should be construed merely as typical and not as limiting the invention, the scope of which is defined in the appending claims. Although for convenience of description, the (a) record has been referred to in the "specification as reduced to a constant standard intensity or amplitude, this intensity oramplitude need not be constant, but may be arbitrarily 'changed to any desired value.

What is claimed is:

1. The method of recoi ding waves which comprises producing a record of the variations in amplitude of the waves and pro ducing another record of the structure of said waves modified as to amplitude.

2. The method of recording waves which comprises producing a. record of the varying amplitudes of. the waves and producing another record of the harmonic structure of said waves reduced to an arbitrary standard amplitude.

3. The method of recording waves which comprises producing a record of the am litudes of the waves and producing anot ier record of the instantaneous phase variations of said waves, said other record being reduced to an arbitrary amplitude.

4. The method of recording sound, which comprises producing a record of the variations in intensity of the sound and producing a second record of the sounds reduced to an arbitrary standard intensity.

5. The method of recording sound waves which consists in producing arecord of the amplitudes of the sound waves,'-. and produc- 7. The method of recording waves which consists in amplifying the waves, regulating the degree of amplification of said waves in accordance with variations in am litude of said waves, utilizin said ampli ed waves for making a recor of the harmonic structure of said waves, and producing another record of the variations in amplitude of said waves.

source of waves of vary 8. The method of recordin waves, which comprises producing a uni- 'rectional pul-' sating current varying in accordance with variations in the amplitude of the waves,

utilizing said current to make a record of said variations in amplitude, amplifying said waves, utilizing said current also to nontrol the degree of am lification inversely as the amplitude of sai waves and utilizing the amplified waves for ma 'ng a second record of the waves.

9. In a recording system, a source of waves, means for recording the variations in am litude of said waves, and means..for

' the structure of said waves, means for controlling the amplitude of said waves in accordance with the intensity of sounds, and means. for recording variations in said sound intensities.

12. A recording system comprising a amplitudes, an amplifier supplied with said waves, means for regulating the degree of amplification imparted to said waves, a wave responsive device arrangedto control said regulating means in accordance with variations in intensity of said waves and a recording device controlled by said amplifier.

13. A recording system which comprises a source of waves of varying amplitudes, an am lifier supplied with said waves, means or regulating the degree of amplification of said waves, a wave responsive device arranged to control said regulating means in accordance with variations in amplitude of said waves, a recording device controlled b said amplifier, and means for recording t e variations in amplitude of said waves.

14. In combination, a source of waves, an amplifier supplied with said waves, means for supplying a uni-directional, pulsating voltage varying in accordance with the amplitude of said waves to said amplifier for regulatingthe degree of amplification of said waves, and a recording device. controlled by said amplifier. l

15. In a recording system, a sourceof waves, an amplifier supplied with said waves, means for *producing a uni-directional, pulsating current of low frequency varying in accordance'with variations in amplitudeofsaid waves, a recording device controlled by said current,- the degree of amplification of said waves supplied to said amplifier being also controlled b said cur rent, and a second recording evice controlled by said amplifier.

16. In a recording system, a source of. sound waves, means for obtaining an amplified, rectified current varying in accordance with variations in the amplitude of said waves, a recording device controlled by said varying current, an amplifying device supplied with said waves. a regulating device supplied with said rectified current for con-' trolling the amplification of said waves suppl 1ed to said amplifying device in accordance w1th variations in said current, and a second Eecording device controlled by said ampli- 17. In a recording system, a source of i sound waves of varying intensity, a regulatmg device supplied with said waves, means for varying the amplification of said waves supplied to said regulating device inversely as the intensity of said waves, means for recording the waves as modified by said first mentioned means, and means for making a a record of variations in amplitude of said sound waves 1 18. A method of producing a wave from wave records which comprises regulating the output of a record of certain characteristics of a wave with the outputof a record of other characteristics of said wave, and controlling a receivingdevice with the resultant ontput of said records so that said wave is reproduced with all of said characteristics.-

19. A method of reproducing sound from two sound records upon which are recorded different characteristics of the same source of sound waves, one of said records representing the harmonic structure of a sound wave and the other of said records representing the varying amplitudes of said wave which comprises transforming the output or each of said records into corresponding-electrical variations, impressing the variations corresponding to the output of the first mentioned record on the input circuit of an amplifying device superimposing thereon the variations corresponding to the output of the second mentioned record of the amplitudes of said wave, regulating theamplification of said variations corresponding to said first mentioned record with the variations correa 0 I spondlng to said second mentioned record another record representing other characteristics of the same wave, a receiving device,-

and means for controlling said receiving device with the output of said records whereby a wave is produced having all of the characteristics of said wave.

21. In a reproducing system a record representing the varying amplitude of a wave,-

.w'a've, a receiving device, and means for controlling said receiving device with. said records whereby said wave is reproduced accurately in wave form and amplitude.

23, In a reproducing system, a record of the varying am litudes of a sound wave, another record 0 the structure of said wave means for controlling the output of said second mentioned record with the output of said first mentioned record so as to obtain a resultant output having the same amplitudes and thesame wave form as said sound wave, and means for transforming said output into sound energy. I

24. In a reproducing system, a record of the varying amplitudes of a sound wave another record of the harmonic structure of said wave, means fortransforming the output 6: each 61 as wares 'into electrical vdri- V ations, means for amplifying the variations correspondin to the output of the first men-' resultant outputfandmeans' for trans or ing said output into sound energ.

25. In a reproducingsystem, a record of .the varying amplitudes of a sound wave,

another record of the harmonic structure of said wave, means for transforming the outputof each of said records into electrical variatio'n's', means for regulating the amplification 'of the variations corresponding to the second mentioned record with the varia tions corresponding to the'first-mentioned record, and means for transforming the re-' sultant variations into sound energy.

In witness whereof, I hereuntosubscribe.

my name this 29th day of April A. D..' 1924.

CHARLES F. SACIA.