US2009229A - System for reproducing sound from a sound record - Google Patents

Description

M 23, was.

J. H. HAMMOND, JR 2,009,229

SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD Original Filed Oct. 14. 1931 4 Sheets-Sheet l Jufly 23, 19350 SYSTEM FOR REPRODUCING SOUND FROMA SOUND RECORD J. H. HAMMOND, JR

Original Filed Oct'. 14, 1951 4 Sheets-Sheet 2' flttenuatmn Decibels I l I l I I I Freq ue ncy QZwM-Cs Wei nuts awuemboz Y 1935 J. H. HAMMOND, JR 2,009,22

' SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD Original Filed Oct. 14, 1931 4 Sheets-Sheet s RECORD $123 23, 1935 J. H. HAMMOND, JR

SYSTEM FOR REPRODUCING SOUND FROM A SOUND Original Filed Oct. 14, 1931 4 Sheets-Sheet 4 fier so that the higher Patented July 23, 1935;

SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD John Hays Hammond, Jr., Gloucester,

October 14, 1931, Serial No. 568,689

Application Mass.

Renewed October 5, 1933 28 Claims. (01. ms-100.1)

This invention relates to amplifying systems in which certain frequencies are discriminated against in accordance with the strength of the output signal, and provides for the elimination of certain desired high frequencies such as scratch and ground noise when the output signal of the system is low, but allows the passage of the high frequencies when the intensity thereof is high.

This invention relates to amplifying systems in which certain frequencies are discriminated against except when their intensity is above a certain value.

The invention also provides for varying the ratio of the high and low frequency notes in accordance with the output volume of the amplifrequencies are discriminated against when the output signal is small and the lower frequencies are discriminated against when the output signal is large.

This invention further provides means for varying the amplification of the system in accordance with the strength of the impressed signal whereby the volume ratio is caused to approximate that of the original production.

In order to control the ratio of amplification for different tone frequencies, a filter is included in the input circuit of the amplifier and means is provided for varying the characteristics of the filter in accordance with the volume of the output signal. Said means is so arranged that the filter is caused to discriminate against high frequencies when the output volume is low and to discriminate against low frequencies when the output volume is high.

The invention is particularly applicable to an amplifier for use with an electric phonograph pick-up or photoelectric pick-up and will be particularly described with reference thereto. It is obvious, however, that it is capable of various other uses.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto. the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which Fig. l is a schematic diagram of an amplifying system constructed in accordance with the present invention.

Fig. 2 is a schematic diagram of a modified form of the filter circuit shown in Fig. 1.

Fig. 3 is a series of curves illustrating the rela- 5 tion between the frequency and the transmitted decibels of the various combinations of circuits as shown in Fig. 2.

Fig. 4 is a schematic diagram of a modified form of filter circuit using magnetic inductance. 10

Fig. 5 is a curve depicting the magnetic changes in the circuit.

Fig. 6 is a schematic diagram of an amplifying system constructed in accordance with the present invention.

Like reference characters denote like parts in the several figures of the drawings.

In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic 20 in their application to similar parts as the art will permit.

Referring more particularly to the drawings, Fig. 1 shows an amplifying system which receives its energy from a phonographic pick-up In or a photo-electric cell II. This cell receives light from a lamp |2 which is energized by a source of power l3. The light from this lamp is focused by a lens M through an aperture |5 in an aperture plate l6 upon the sound record of a moving film IT. The light which passes through this film then impinges upon the photoelectric cell II. This cell is connected through a transformer i8 to two contacts 2| of a double-pole double-throw switch, 22, the other contacts 23 of which are connected to the phonographic pick-up in.

The blades of the switch 22 are connected to the primary of a transformer 24, the secondary of which is connected through a scratch or low pass filter network 25 to a pentiometer 26. This potentiometer 26 is connected across a transformer 21 the secondary of which is connected to the input circuit of a space discharge amplifier 3|. The grid return of this amplifier includes a resistance 34 and battery 33 and is connected to the moveable arm of a potentiometer 32.

A condenser 35 is shunted across the resistance 34 which is connected in circuit with a rectifier 36 and the secondary of a transformer 31. The primary of this transformer is included in the plate circuit of a space discharge means 38, the grid of which is connected through a blocking condenser M to the input circuit of the space discharge means 3|.

The output circuit of the space discharge means 3| is connected to the primary of a transformer 44 which is shunted by a resistance 45. The secondary of the transformer 44 is connected to a filter circuit 46 which includes condensers 41 and 48, the circuits of which are controlled by relays 5| and 52, respectively. When condensers 41 and 48 are connected in circuit, the filter 46 operates as a low pass filter and when the condensers are disconnected the transmission characteristics of the filter are altered so as to allow more of the high frequencies to pass. The secondary of the transformer 44 is also connected through a high pass filter network 53 to the primary of a transformer 54. The secondary of this transformer is connected through a potentiometer 55 to the input circuit of a space discharge device 51. The output circuit of this device includes the windings of the relays 5| and 52 in series.

The filter network 46 is connected to the primary of a transformer 6| the secondary of which is connected to the input circuit of a push-pull amplifier 62, the output circuit of which is connected through a transformer 63 to the moving coil of a loud speaker 64. The field winding 65 of this loud speaker is supplied with current from a battery 66.

In the operation of the form of the invention shown in Fig. 1 the switch 2| is thrown up if it is desired to use the moving picture projector, and down if it is desired to use the phonograph. In either case, the energy received from the photoelectric cell H or the pick-up device it passes through the transformer 24 and filter cir+ cuit 25 to the potentiometer 26. Here any desired amount of energy may be selected by manually operating the moveable contact of this device. The energy thus selected is fed through the transformer 21 to the input circuit of the space discharge means 3|. Some of this energy also passes through the blocking condenser 4| to the space discharge means 38 where it is amplified and passes through the primary of the transformer-31. The current in the secondary of this transformer is rectified by a rectifier 36 and passes through the resistance 34 in the direction of the arrow, thus building up a potential difference across this resistance which is dependent upon the strength of the input signal so that this potential difference increases with the increase of signal strength. As this potential increases it causes a decrease of the negative bias on the grid of space discharge means 3| thus decreasing its impedance, and therefore increasing its amplification ratio.

The amplified current from the space discharge means 3| then passes through the transformer 44 to the filter circuit 46, where any high frequency currents such as those produced by scratch and ground noise are eliminated when relays 5| and 52 are in the position shown. The energy from this filter circuit passes through the transformer 6| and is amplified by the push-pull amplifier 62. This amplified energy then passes through the transformer 63 to the loud speaker 64 where it is reproduced as speech or music.

Some of the energy from the secondary of the transformer 44 passes through the filter network 53 where the low frequency currents are eliminated. If there are high frequency currents present in the circuit, they pass through this network and the transformer 54 to the input circuit of the space discharge means 51 which is biased for plate rectification. The rectified current from the space discharge means 51 passes through the relays 5| and 52, and, when of sufiicient strength, breaks the circuits through the condensers 41 and 48 causing the filter 46 to operate as a high pass filter whereby high frequency currents are allowed to pass through this network. These currents together with the low frequency currents present are then amplified by the push pull amplifier 62 and reproduced in the loud speaker 64;

The adjustment is such that when no high fre quency currents are present in the speech or music the filter network 46 will operate to eliminate any undesirable ground noise or needle scratch which may be present. If high frequency currents are present in the speech or music, however, in' substantial amplitude, these will act to change the characteristics of the filter circuit 46 so as to allow them, together with any scratch or ground noise and the lower frequencies to pass through and be reproduced in the loud speaker. When these high frequency tones are present in sufiicient volume to operate the device, the scratch and ground noise will be so small in comparison that they will not prove objectionable in the speech or music reproduced in the loud speaker. The filter 46 discriminates against the lower frequencies when there are high frequencies present in sufficient intensity, thus increasing the brilliance of the sound with large volumes.

In the modified form of the invention shown in Figure 2, the secondary of the transformer 44 is connected in the input circuit of a space discharge means II, the output circuit of which includes an iron core inductance l2 and a plate battery 13. Connected to this output circuit is a low pass filter circuit 14 which includes two inductances l5 and 16, and two condensers 11 and 18. The circuits of these devices are controlled by two relays 8| and 82. The output side of the filter circuit 14 is connected through a potentiometer 83 to the primary of the transformer 6|.

Also, connected across the output circuit of the space discharge means H is a high-pass filter circuit 84, the output of which is connected through a transformer 85 to a potentiometer 86. The movable contact of this potentiometer is connected through grid leak and condenser 81 to the grid of a space discharge means 88. The output circuit of this device is connected to the windings of the relays 8| and 82.

In the operation of the modified form of the invention shown in Fig. 2, the pick-up'device and amplifier function as described in connection with Fig. 1. The energy which passes through the transformer 44 is then amplified by the space discharge means H and passes through the filter circuit '14 to the transformer 6|, thence through the push-pull amplifier 62 to the loud speaker 64 as already described.

When high frequency currents are present they pass through the high-pass filter 84 and the transformer 85. From the secondary of this transformer the energy passes to the potentiometer 86 where any desired portion of it may be picked up and fed,to the grid circuit of tube 88 where rectification takes place, this rectified current causing a negative potential to be built up upon the grid of the space discharge means 88. If the strength of the high frequency currents is sufficient, the bias produced will be sufficient to increase the impedance of the space discharge means 88 so that practically no current will be passed by it, thus causing the relays 8| and 82 to be de-energized as shown in Fig. 2. This causes the circuits through the condensers I1 and 18 to be broken and the inductances 15 and 18 short-circuited, thus making the filter circuit 14 inoperative so that all frequencies both high and low will be passed through it.

If, however, the high frequency currents are not present, or else of very low intensity, no energy will be passed through the filter circuit 84, and therefore there will be no current rectified by the grid leak and condenser 81. There will, under these conditions, be very little bias on the space discharge means 88 so that this will pass a large amount of current, thus operating the relays BI and 82 so as to cause the filter circuit 14 to become operative and cut out any high frequency tones such as scratch or ground noise which may be present.

It is understood that the system is not limited to the types of filter circuits shown in the accompanying drawings, but that any suitable or equivalent system may be employed or that the number and arrangement of the inductances and capacities as shown in these figures may be varied as desired.

In Fig. 3 the curve 9| represents the operation of the filter system I4 when both relays BI and 82 are energized. This curve shows the relation between the frequency and the attenuation in decibels. This is the curve for the normal operation of the filter circuit I4. By the proper design of the relays BI and 82, and the spring tensions of the armatures, it is possible to have one relay open sooner than the other, or for one or the other. of the relays to remain in an intermediate position. Thus, for example, if either relay 8| or 82 were part way up so as not to engage either contact, the system would function as shown by the curve 32. If one relay is entirely de-energized so that its armature engages the upper contact, and the other relay is energized so that its armature engages the lower contact, the operation of the system would be as shown by the curve 93. If one relay is entirely de-energized and the other relay partly so, so that its armature does not engage either contact, the operation of the system will be as shown by curve 90. If both relays are deenergized, the filter circuit 10 will be made entirely inoperative, and the operation of the system will be depicted by the straight line 95..

The operation of the system is not limited to the curves shown in Fig. 3, as by a proper selection of the constants of the filter circuit I0, and the proper design of the relays BI and 02, any desired curve between the limits of normal operation, shown by curve SI, and the straight line 95 may be obtained.

In the modified form of the invention shown in Fig. 4, one side of the secondary of the transformer M is connected through three choke coils I0 I, H32, and I03 to one side of the primary of the transformer GI. The other side of the secondary of the transformer 4 is connected through a battery I00 to the other side of the primary 0i. Across the secondary of the transformer Ml is connected a high pass filter circuit I05, the other side of which is connected to the primary of a transformer I06. The secondary of this transformer is connected to-the input circuits of three space discharge means I01, I00, and I09. The output circuits of these devices ahe connected throughchokecoils II I, I I2, and I I3 to three windings H4, H5 and H6 which are wound on the same cores as the choke coils IOI, I02 and I03. Across the output circuits of the devices I0'I, I00, I09 are condensers II'I, M0 and H9.

' invention, shown in Fig.

.densers H1, H8 and IIS and chokes III,

modified form of the 4, when no high frequency tone energy is present at secondary 44, the scratch or high frequency stray tones are prevented from reaching primary BI by filter action due to chokes IOI, I02, I03, and associated circuits. When high frequency tones pass through the high pass filter I05 and energize space discharge means I01, I08 and I09, operating as biased rectifiers, the plate currents increase, increasing magnetization of the cores of chokes. IOI, I02 and I03, and diminishing their choking action in a well known manner, illustrated by Fig. 5. Con- II2 and H3 serve to eliminate tone'frequencies from entering the output system by transformer action with H4, H5 and H6 as primaries, and IOI, I02 and I03, as secondaries. These choke and condensers also serve in minimizing change of impedance characteristics of WI, to variable impedances of the tubes I01, I08 and I09, so that only change in plate direct current is operative in controlling the filtering action.

This arrangement may be modified if desired In the operation of the by inserting a rectifier and low pass filter between transformer I06 and grids of tubes I01, I08 and. I09, so that tone currents are excluded from plate circuits of the tubes, with however, the plate current of the tubes rising and internal impedances of the tubes lowering with increase tone signal. In this case, con- II9 and chokes III, H2 and and the filtering characteristics of windings IOI, I02 and I03 will be altered in two manners, first by the variation in magnetizing force of their cores, and second by variable loading of windings H4, H5 and H6 which act as secondaries. As is well-known, lowering the secondary load resistance, in this case by deof high frequency densers I I1, H8, H3 may be omitted,

crease of the internal impedance of the tube,

results in a lowered equivalent primary impedance and lower choking action. The transformer effect of variable loading and the core magnetization effect thus additively cooperate in reducing the choke action as the high frequency tone energy increases.

As a result, with the circuit of Fig. 4, as shown or modified to permit transformer action, the transmission factor for high frequency energy from 44 to SI increases with increase of high frequency tone energy in a continuous manner, so

that an automatic scratch filter is provided with reduced filter action as the desired high frequency tones increase.

In the modified form of the invention shown in Fig. 6 an amplifying system is shown which receives its energy from a phonograph pick-up 2'I0, or a photo-electric cell 2. This cell receives light from a lamp 2I2, which is energized from a source of power 2I3. The light from this .lamp is focused by a lens 2M, through an aperture 2 I 5 in an aperture plate 2 I 0, upon the sound record of a moving film 2II. The light which passes through this film then impinges upon the photoelectric cell 2i I. This cell. is connected through a transformer 2I8 to two contacts 22I, of a double pole, double throw switch222, the other contacts 223 of which are connected to the phonograph pick-up 2 I0.

Theblades of the switch 222 are connected through transformer 224 and a variable filter circuit 225 to a potentiometer 226. The filter circuit 225 may consist of series inductances 23I, 232 and 233, and parallel condensers, 234 and I02 and I03, due

235, which are connected relays 236 and 237.

The potentiometer 226 is connected across the primary of a transformer 24!, the secondary of which is in the input circuit of a space discharge means 243. The grid return of the space discharge means 243 includes a resistance 245 and battery 244 and is connected to potentiometer N3. Resistance 245 is shunted by a. condenser 246 and is connected in circuit with rectifier 241 which is in series with the secondary of a transformer 248. The primary of this transformer is included in the plate circuit of a space discharge means 25!, the grid of which is connected through a blocking condenser 253 to the secondary of transformer 24!.

The output circuit of the space discharge means 263 is connected to the primary of a transformer 255 which is shunted with a resistance 255. The secondary of a transformer 255 is connected to the input circuit of a space discharge means 25]. The output circuit of this device is connected to to the contacts of two the primary of a transformer 258. The secondary of the transformer 258 is connected to the input circuit of a push-pull amplifier 26], the output circuit of which is connected to the primary of a transformer 262, the secondary of which is connected to the moving coil of a loud speaker 263 the field winding 26 3 of which is supplied with current from a battery 2%.

l The output circuit of the push-pull amplifier 268 is also connected through a low pass filter network 266 and transformer 26? to the input circult of a space discharge means 258 including a grid leak 271i. The output circuit of the space discharge means 258 is connected to the relays 235 and 237! the return from which passes to an adjustable tap on the plate battery 2'i2. A condenser 2'53 is connected across the relays 236 and In the operation of the modified form of the invention shown in Fig. 6, when it is desired to use the photoelectric pickup system the switch 222m thrown in the up position. Light from the lamp 2M? is then focused by the lens 2 !4 through the aperture 2i5 and upon the sound track of the film 2H. The fluctuating light which passes through this sound track then impinges upon the photoelectric cell 2 causing a corresponding pulsating current to flow in the primary of the transformer 2&8. The current from the secon-- dary of thistransformer then passes through the transformer 224 and filter network 225 to the potentiometer 225.

With the relays 236 and 231 in the closed position, as shown, the condensers 234 and 235 are connected and the filter network 225 will operate as a low pass filter and cut out any high frequency vibrations which may be present. The energy which passes said filter is applied to the input circuit of the space discharge means 243, the bias of which is determined conJointly by the setting of the potentiometer I43, the voltage of the battery 244, and the potential drop in resistance 245. Some of the energy from the secondary of the transformer 2 passes through the blocking condenser 253 which is connected to this current increases. This increases the gain ratio of the amplifier 243, thus increasing the output of this device, which in turn increases the sound produced by the loud speaker 262. In this way as the energy input to the space discharge means 243 is increased the gain ratio of this device will also be increased so that the amplification will vary in accordance with the signal strength, being greater for strong signals than for weak signals. Resistance 256 serves to keep the frequency characteristics of the amplifier independent of the amplitude characteristics.

The energy from the output circuit of the space discharge means 243 passes through the transformer 255 to the space discharge means 251 where it is further amplified and passes through the transformer 258 to the push-pull amplifier 26f where it is again amplified and sent through the transformer 262 to the loud speaker 263 where it reproduces the sound in the usual manner.

Some of the output energy from the pushpull amplifier 26| passes into the filter network 266 which allows low frequency currents to pass if they are present. These low frequency currents then pass through the transformer 26! from the secondary of which they pass to the input circuit of the space discharge means 268 in which they are rectified and fiow in the direction of the arrow through resistance 2M. Thus, as these currents increase in intensity, they cause the bias of the tube 268 to be increased, thereby re-.

ducing the plate current of this device. As. this current is reduced below a certain value, the relays 236 and 23? will be opened under the action of their springs, thus disconnecting the condensers 234 and 235 in the filter network 225. When this occurs this filter network will allow the high frequency currents to pass and will discriminate against low frequency currents.

It is thus seen that when there is very little energy passing through the system the condensers 234 and 235 will be operative thereby cutting out any high frequency vibrations such as scratch or ground noise which may be present. When the energy through the system increases so that there is a considerable volume of low frequency energy directed into the loud speaker, the relays 236 and 231 will'be opened thereby allowing the higher frequencies to pass through the filter network 225 together with the lower frequencies. The scratch and ground noise will also pass at this time, but as the volume of sound produced is large, these noises will not be objectionable.

It is evident, therefore, that when the total output is small and the scratch and ground noise would be heard clearly, they are eliminated; and when the output is large so that they would not be conspicuous, they are allowed to pass together with the tones which may be present in the speech or music.

If it is desired to use the phonograph pick-up m the switch 222 is thrown in the down position. The energy, from the pick-up device 2" then passes through this switch to the transformer 224. From; here on the operation is similar to that described in connection with the photoelectric system.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be lmderstood that various ommissions, substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A system of sound transfer utilizing a sound record comprising means controlled by the volume of the high frequency components of the sound for discriminating against certain frequencies when the total volume is small and against other frequencies when the total volume is large,

2. A system of sound transfer utilizing a sound record comprising means controlled by the volume of the high frequency components of the sound for discriminating against high frequencies when the total volume is small and against low frequencies when the total volume is large.

3. A system for producing sound from a sound record including pick-up means, transducing means and a sound propagating means, said system having a filter network associated therewith having variable transmission characteristics and means controlled by the strength of the high frequency components of the signal for varying said transmission characteristics and causing said system to discriminate against certain frequencies when the signal strength is large and against other frequencies when the signal strength is small.

4. A system for producing sound from a sound record including pick-up means, transducing means and a sound propagating means, said system having a filter network associated therewith having variable transmission characteristics and means controlled by the strength of the high frequency components of the signal for varying said transmission characteristics and causing said system to discriminate against low frequencies when the signal strength is large and against high frequencies when the signal strength is small.

5. A system for producing sound from a sound record comprising a pick-up device, a transmission channel and sound propagating means and means controlled in accordance with the distribution and strength of the high frequency components of the signal for causing said channel to relatively discriminate more against high frequencies when the high frequency components are weak or when the total signal strength is small.

6. A system for producing sound from a sound record comprising a pickp device, amplifier and sound propagating means, a filter network associated with said amplifier and having variable transmission characteristics, means progressively more responsive to the high frequency components of the signal for controlling said transm'ssion characteristics so that said filter is caused to discriminate against high frequency signals when the output volume is small and to progressively discriminate less against said high frequency components when the total volume increases or when the frequency distribution changes toward the higher frequencies.

'7. A system for producing sound from a sound record comprising an amplifier and a sound prop- .connected with the input circuit of said amplifier and controlled in accordance with the high frequency component of the signal in the output circuit of said amplifier to discriminate against high frequencies when said'output signal is small and to discriminate against low frequencies when said output signal is large.

8. A system for producing sound from a sound record comprising an amplifier and a sound propagating device, a filter network connected with the input circuit of said amplifier, said network having series elements and parallel elements, re- I lays for connecting and disconnecting said parallel elements and means controlled by the output signal strength for operating said relays.

9. A system for producing sound from a sound record comprising an amplifier and a sound propagating device, a filter network connected with the input circuit of said amplifier, said network having series elements and parallel elements, relays for connecting and disconnecting said parallel elements and means controlled by the low frequency components of the output signal for operating said relays.

10. A system for producing sound from a sound record comprising an amplifier and a sound propagating device, a filter network connected in the input circuit of said amplifier and normally operating to discriminate against high frequency signals, a relay for" controlling said network and causing the same to discriminate against low frequency signals and means including a low pass filter and a rectifier associated with the output circuit of the amplifier for causing said relay to operate when the low frequency component of the output signal exceeds a predetermined value.

11. In a system for producing sound from a sound record, a transducer, a filter circuit associated therewith and normally serving to suppress signals of certain frequencies and'a control circuit associated with said transducer, said control circuit discriminating in favor of the high frequency components of said signals and being adapted to reduce the suppression of said certain frequencies by said filter circuit in response to an increase in said certain frequencies or to a change in frequency distribution toward said certain frequencies.

12. In a system for producing sound from a sound record including an amplifier, a filter network associated therewith, and normally adapted to suppress high frequency signals, and means controlled-by the strength of said high frequency signals to cause said filter network to pass the same when they are present in excess of a predetermined amount.

13. In a system for producing sound from a sound record including a pick-up, a transducer and a sound producing device, a filter network for normally discriminating against signals of certain frequencies and means controlled in accordance with the strength of said signals for altering the characteristics of said network so that the amount of discrimination is diminished as the strength of said signals is increased.

14. In a system-for producing sound from a sound record including a pick-up, a transducer and a sound producing device, a filter network for normally discriminating against high frequency signals and means controlled in accordance with the strength of said high frequency signals for altering the characteristi -s of said network so that the amount of discrimination is diminished as the strengths of said signals are increased.

15. In an electric circuit, a filter adapted to suppress signals of certain frequencies and means controlled by the intensity of the suppressed signals for varying whereby the relative suppression is varied inversely as the strength of said signals is increased.

16. In a system for producing sound from a.

the characteristics of said filter sound record, a filter network tween said amplifier sound record, a filter network adapted normally to suppress signals of certain frequencies, a control circuit operated by said signals, a relay associated with said control circuit and means whereby said relay changes the characteristics of said filter network and permits said signals to be passed thereby.

17. In a system for producing sound from 9. adapted normally to suppress high frequency signals, a control circuit operated by said high frequency signals, a relay means whereby said relay changes the characteristic of said filter network and permits said high frequency signals to be passed thereby.

18. In a system for reproducing sound, a sound record, a pick-up therefor, an amplifier fed by said pick-up, means for controlling the gain ratio of said amplifier in accordance with the dynamics of said record, a translating device fed by said amplifier, a variable filter between said amplifier and translating device, and means controlled by the sound volume for varying the constants of said filter.

19. In a system for reproducing sound, a sound record, a pick-up device therefor, a dynamic amplifier fed by said pick-up device, a translating device fed by said amplifier, a variable filter beand translating device, a control circuit connected between said amplifier and filter, a high pass filter in said control cir cult, and means for varying the constantsof said variable filter by said control circuit.

20. A system for reproducing sound, a sound record. a pick-up device therefor, a dynamic amplifier fed by said pick-up device, a translating device fed by said amplifier, a variable filter be-' tween said amplifier and translating device normally discriminating against high frequency tones. a control circuit connected between said amplifier and filter, a high pass filter in said control circuit, and means for varying the constants of said variable filter by said control ciredit in such manner that when high frequency tones are present in sumcient volume to pass through said high pass filter, said variable filter also passes high frequency tones.

21. In a system of sound transfer utilizing a sound record, a translating device, a sound record, means for transferring energy between said translating device and said sound record including a variable filter, said variable filter comprising a pair of inductances, parallel branch circuits across the opposite sides of said inductances, each branch circuit comprising a pair of capacitances and a switch therebetween all serially connected, a relay for each switch and means for controlling said relays according to variations in the sound energy.

22. In a system of sound transfer utilizing a sound record, a translating device, a sound record, means for transferring energy between said translating device and said sound record including a variable filter, said variable filter comprising a pair of reactances of one kind, parallel branch circuits across the opposite sides of said reactances, each branch circuit com a reactance of opposite kind and a switch serially connected, a relay for each switch, and means for associated with said control circuit andcontrolling said relays according to variation in the sound energy.

23. In a system of sound transfer utilizing a sound record, a translating device, a sound record, means for transferring energy between said translating device and said sound record including a variable filter, said variable filter comprising a pair of reactances of one kind, parallel branch circuits across the opposite sides of said reactances, each branch circuit comprising a reactance of opposite kind, and a switch serially connected, a relay for each switch, a control circuit passing energy varying according to the sound, both relays being fed by said control circult, and means for causing one relay to operate before the other.

24. The method of operating an amplifier in t e reproduction of sound from a sound record which comprises controlling the relative volume of different frequency components in accordance with the frequency distribution and with the total volume of the sound energy.

25. In a system for producing sound from a sound record, a pick-up device, a transmission device and sound propagating means, means to vary the relative transmission characteristics of said device for different frequency components, and means governed exclusively by the high frequency components of the signal adapted to control said first means for causing said transmission device to discriminate more against high frequencies than against low frequencies, only when the signal strength of the high frequencies is below scratch levels.

26. In a system for producing sound from a sound record, a transducer, a filter circuit asso ciated therewith and normally serving to suppress the high frequency components of the signals and a control circuit associated with said transducer, said control circuit discriminating in favor of the high frequency components of said signals and being adapted to reduce the supprm-= sion of said components by said filter circuit in response to an increase in strength of the in frequency components or in response to a cge in frequency distribution oward the high frequencies. I

27. In a system for reproducing sound from a sound record, a transmission channel having a filter adapted to variably suppress the high frequency components of the sound, means responsive tothe sound energy to progressively reduce the suppression'of said high frequency components by said filter and means whereby high frequencies exert a greater influence than low frequencies on said last means.

28. In a system for reproducing sound from a sound record, a transmission channel having a filter adapted to variably suppress the high frequency components of the sound, a control channel supplied with sound energy from said record and adapted to progressively reduce the suppression of high frequencies by said filter as the energy transmitted through said control channel increases, and means associated with said control channel for discriminating in favor of high frequencies whereby the high frequencies exert a greater influence than low frequencies on said filter.

JOHN HAYS HAMMOND, Jr.

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