US3153702A

US3153702A - Volume compensated stereophonic phonograph

Info

Publication number: US3153702A
Application number: US8150A
Authority: US
Inventors: Ralph H Janowsky; John H Riggs
Original assignee: Wurlitzer Co
Current assignee: Wurlitzer Co
Priority date: 1960-02-11
Filing date: 1960-02-11
Publication date: 1964-10-20
Anticipated expiration: 1981-10-20

Description

Filed Feb. l1, 1960 R. H. JANowsKY ETAL VOLUME COMPENSATED STEREOPHONIC PHONOGRAPH 01m/mel E VVV' All!

Oct. 20, 1964 United States Patent (IT-)ii ice Bassist Patented Oct. 20, 1964 3,153,702 VLUME COMPENSATED STEREPHNXC PHNGGRAPH Ralph H. .lanowshy, Lockport, and John H. Riggs, Kenmore, NSY., assignors to The Wurlitzer Company,

Chicago, lll., a corporation of @hie Filed Feb. 11, 1960, Ser. No. 3,15% 3 Claims. (Cl. 179-1) This invention relates to stereophonic sound systems adapted to automatically play a sequence of stereophonic recordings, such for example as stereophonic records. Stereophonic records are played automatically by coin controlled phonographs or jukeboxes and by automatic background music systems.

Such automatic sound systems are designed to operate unattended to reproduce a succession of recordings at a volumetric level which is sufficiently high to assure enjoyment of the music by those for whom the recordings are played. Yet, it is also extremely desirable that the loudness level at which the recordings are reproduced be limited sufliciently to avoid disturbance or irritation of people within the audible range of the reproduction system.

The problem of maintaining the volumetric output level of an automatic phonograph within the optimum limits while the machine operates unattended over long periods is complicated by the fact that diterent records are recorded to have different degrees of inherent loudness. Thus, a degree of ampliication which provides an optimum loudness in the reproduction of a record having a relatively low inherent loudness may produce excessive loudness in the acoustical reproduction of a recording having a relatively high inherent loudness.

The matter of adapting an automatic phonograph, which plays monophonic records exclusively, to compensate automatically for different degrees of loudness of the records played has been accomplished satisfactorily. However, the problem of providing for automatic compensation for different degrees of inherent loudness in stereophonic records presents many complicated problems in the designing of automatic stereophonic phonograph systems. These problems which are peculiar to stereophonic phonograph systems make the expedients used in monophonic systems to compensate for difterent degrees of inherent loudness of monophonic records unsuitable for use in stereophonic phonograph systems.

One object of the invention is to provide, for reproducing stereophonic records, a new and improved stereophonic sound system which preserves the mutual independence of two sound channels used in the system, and hence maximizes the stereophonic effectiveness of the reproduced sounds, while at the same time operating automatically to provide a highly effective control of the acoustical loudness of the system to compensate for different degrees of loudness of the successive records played.

Another object is to provide an automatic stereophonic phonograph or sound system of the character recited in the preceding object which responds accurately and with great etiiciency to dilferences in the inherent loudness of recordings, to accurately compensate for the differences in the inherent loudness of the recordings to maintain an optimum acoustical output level in the stereophonic reproduction of the recordings, while the the same time preserving the full stereophonic character of the reproduced sound.

A further object is to provide, in an automatic phonograph, for attenuating the sound signals in an improved manner which is automatically controlled to continuously compensate accurately for the degree of inherent loudness of the successive records played by the phonograph.

Other objects and advantages will become apparent from the following description, taken with reference to the single ligure of the drawing, which constitutes a diagrammatic illustration of a stereophonic phonograph forming the exemplary embodiment of the invention.

Referring to the drawing in greater detail, the automatic, stereophonic phonograph 10 forming the exemplary embodiment of the invention to be described is illustrated diagrammatically in the single figure of the drawing.

In the phonograph itl a succession of records 12 are automatically positioned on a turntable 14 and rotated in association with a stereophonic pickup 16 which supplies independent electrical sound signals through two separate outlets or terminals 18, 2t) of the pickup.

The electric sound signals supplied to the respective pickup outlets l, 20 are separately amplified respectively in two electronic amplifying channels identified in the drawing by the legend Channel A and Channel B, and operating to drive stereophonic loud-speakers 22, 2.4. Thus, the pickup output 18 is coupled through a capacitor 26 with a preamplifier 23 in Channel A which is connected through a conventional tone control 3i) with the Channel A amplifier 32, which drives the loud-speaker 22. Similarly, the pickup outlet 20 is coupled through a capacitor 34 with a preamplifier 36 in Channel B which is connected through a tone control 38 with an amplifier 40, which drives the loud-speaker 24.

As previously intimated, stereophonic records, like monophonic records, have different degrees of inherent loudness. Automatic phonographs, such as the phonograph 10 illustrated, normally operate unattended over long periods of time. In order to maintain the loudness of the acoustical reproduction of the records Within optimum limits, it is desirable to provide some compensation in the system for the inherent loudness of the recordings being played. The problem of accomplishing this desired end is complicated in stereophonic phonograph systems by a number of factors. These include the necessity for maintaining the operating independence of the two sound channels in order to preserve the inherent advantages of stereophonic reproduction of recordings. The expedient of providing automatic volume compensation in each sound channel in accordance with the strength of the signal being amplied in the channel is unsuitable, in that the stereophonic effectiveness of the sound reproduction would be greatly diminished, even though the means used to provide automatic volume compensation in the two channels are structurally and operationally independent of each other. Thus, in order to realize the full advantages of stereophonic sound reproduction, it is necessary that either of the channels be capable of producing relatively loud acoustical sounds.` Thus, in a sense, a contrast in the loudness of sounds generated by the two sound channels is an essential characteristic of fully eifective stereophonic sound reproduction. T o provide automatic volume compensation in each sound channel which is operationally independent of automatic volume compensation in the other channel would result in an undesirable diminution in the differential loudness of the acoustical outputs of the two channels relative to the differential strength or loudness of the electrical sound signals supplied to the two channels.

Further complications arise in properly compensating for different degrees of inherent loudness in stereophonic recordings from the fact that a marked difference in the strength or loudness of the sound signals in the two sound channels may persist for an appreciable period of time, as in the playing of stereophonic recordings of some orchestrations.

The degree to which the acoustical reproduction of a stereophonic recording is excessively loud is a function enea-,vea

of the loudness of the sound produced by the one of the two sound channels which is receiving the stronger input signals from Ithe recording. In accordance with the invention, a highly effective compensation for the inherent loudness of the record being played is provided in a stereophonic phonograph or similar sound system in a manner which preserves the full stereophonic effectiveof the sound reproduction. This is achieved, as will presently appear, by providing volumetric compensation in both channels which is continuously controlled automatically, in accordance with the stronger of the two signals in the respective channels and in a manner which preserves the operational independence of the channels.

Thus, having reference to the drawing, it will be noted that the input side of the coupling capacitor 26 in Channel A is grounded through two resistors 42, 44 connected in series and serving as a voltage divider. A tap 46 to adjacent ends of the resistors 42, 44 is coupled through a capacitor 48 with a volume control amplifier 50 for Channel A.

Preferably, the control amplifier Si) comprises two

transistors

52, 54 connected in cascade between the input coupling capacitor 48 and an output coupling capacitor 56. A power voltage is applied to the amplifier 56B through a conductor 58 connected through a resistor 60 with a power line 62.

The volume control amplifier 64 for Channel B is similar in construction and in its operation to the volume control amplifier 50 for Channel A. The input of the volume control amplifier 64 is coupled through a capacitor 66 and a voltage divider formed by two resistors 63 and '70 with the input side of the input capacitor 345 in Channel B. The circuit of the amplifier 64 includes two transistors 72 and 74 connected in cascade between the input coupling condenser 66 and the output coupling condenser 76. A power voltage is applied to the amplifier 64 by the previously mentioned conductor 58.

The outputs of the two voltage control amplifiers Si), 64 are connected through two rectifiers 73, 3f) with the input side of a filter circuit 82. As shown, the filter circuit 82 comprises a resistor 84 having its input and output ends coupled to ground through two

capacitors

36, 88. A resistor 90 is shunted across the capacitor 88.

The connection of the two rectifiers 78, 8f3 between the outputs of the two volume control circuits Sil, 64 avoids interference of these circuits with each other, while at the same time applying to the input of the filter circuit 32 the electrical output of the one of the amplifiers Sii, 64 which is excited by the stronger of the signals from the two

outputs

18, 20 of the pickup 1d. It may be noted in passing that, if desired, a preamplifying stage can be provided between the pickup outlet 18 and the resistor 42 in Channel A, with a similar preamplifying state being provided between the pickup outlet 2f) and the resistor 68 in Channel B.

The lter circuit 82 has an electrical integrating or averaging action in providing an electrical output at its outlet end 92 which is a function of the output of the more excited one of the

control amplifiers

50, 64 over a short interval of time. By way of example, a suitable filter 82 is formed by a resistor 84 of 47 kilohms,

grounding capacitors

86, 88 of 100 microfarads each and a shunting resistor 9i? of 470 kilohms. A filter 82 formed of components having the exemplary values just recited provides an electrical output which is a functional average of the electrical input to the filter over a period of time that is short in relation to the time required to play a recording but at the same time rather extensive in relation to the time typically required in music to play a note of music. ln fact, the period over which the described filter 82 will average functionally the input to the filter is sufiiciently long to extend over the playing of a number of successive musical notes of normal duration.

The electrical output of the filter circuit 82 is used to control automatic volume compensation means provided in both Channel A and Channel B.

Thus, as illustrated in the drawing, improved signal attenuating means 94 provided in Channel A comprises an attenuating resistor 96 connected between the capacitor T26 and the preamplifier 28. The output side of the attenuating resistor 96 is connected to ground through a bleed resistor 98 and a discharging rectifier 10i). The effective admittance of the rectifier lfl with respect to the signal strength at the output end of the resistor 96 is controlled by the electrical output of the lter circuit 32, which is connected through a rectifier 102 to discharge through the attenuating or bleed rectifier 100. Thus, as shown, the output side of the rectifier 102 is connected to a tap M34 between the bleed resistor 9S and the discharge rectifier idf).

in operation, the filter circuit 82 applies an electrical bias to the discharge rectifier Mit), thus tending to cause the rectifier itt@ to conduct.

Admittance of the bleed rectifier lil@ to the sound signal strength at the output end of the resistor 96, and hence the extent to which this sound signal is bled off through the resistor 93, is controlled by the degree to which the rectifier liifi is biased -to conduct direct current by the filter circuit 82. Hence, increases in the output of the filter circuit 82 effects proportional increases in the degree to which the sound signal strength is bled off through the resistor 98, with an accompanying attenuation of the sound signals by the attenuating resistor 96, to produce the desired volume control in Channel A, which compensates for the inherent loudness of the record being played.

The loudness of Channel B is controlled in a similar manner. rl`hus, as shown7 an attenuating resistor 106 is connected between the capacitor 34 and the preamplifier 36. A bleed resistor 10S is connected from the output end of the resistor 166 to ground through a bleed or attenuating rectifier 119. The output of the filter circuit 82 is connected through a rectifier 112 with the input side of the bleed rectifier il@ to control the admittance of the latter to the sound signals, and hence control the attenuation of the signals through the resistor 106, in accordance with the output of the filter circuit 82, which operates in a manner described to provide the desired overall compensation for the inherent loudness of the record being played.

It will be understood that the invention is not necessarily limited to the particular embodiment illustrated, but includes variants and alternatives within the spirit and scope of the invention as defined by the claims.

The invention is claimed as follows:

1. In a stereophonic amplifier for playing program sources of different inherent loudness and having two amplifying sound channels, the combination comprising two volume control networks having connections with said respective sound channels to vary controllably the volume of electronic sound signals which are transmitted through said respective channels; each of said volume control networks including circuitry that is responsive to a variable control voltage applied thereto to effect a controlled modification of the loudness of the sound signals passing through the corresponding channel, which modification is substantially uniform in degree for all sound signals passing through the associated channel and which is a function of the control voltage applied to the volume control network; a voltage integrating network having an input side and an output side and including circuitry which responds to the application of a variable voltage to the input side of the integrating network to produce an output voltage which is a function of the voltage, averaged over a period of time that is sufficiently long to encompass the playing of a number of musical notes of normal duration, that is applied to the input side of the integrating network; means including two rectifiers connecting the input side of said voltage integrating network to said respective sound channels ahead of the connections with the sound channels of said respective control networks to maintain the independence of said channels and at the same time apply to the input side of said integrating network a voltage which is a function of the loudness of the louder of the two sound signals in said channels, and means including two rectitiers connecting the output side of said integrating network in controlling relation to said respective control networks.

2. In a stereophonic music system, the combination of two separate parallel channels for electronic music signals, two volume control networks having connections with said respective channels to vary controllably the volume of electronic music signals which are transmitted through said respective channels; each of said volume control networks including circuitry that is responsive to a variable control voltage applied thereto to effect a controlled modification of the loudness of the electronic music signals passing through the corresponding channel, which modication is substantially uniform in degree for all sound signals passing through the corresponding channel and which is a function of the control voltage applied to the volume control network; a voltage integrating network having an input side and an output side and including voltage integrating circuitry which responds to the application of a variable voltage to the input side of the integrating network to produce an output voltage which is a function of the voltage applied to the input side of the integrating network and which output voltage is increased and decreased by said voltage integrating circuitry only in response to increases and decreases respectively in the voltage applied to the input of the integrating network and averaged over a period of time equal to the average time required to play a number of normal musical notes in succession, means including two rectiliers connecting the input side of said integrating network to said respective sound channels to maintain the independence of said channels and at the same time apply to the input side of said integrating network a voltage which is a function of the loudness of the louder of the two sound signals in said channels, and means connecting the output side of said integrating network in controlling relation to said respective control networks, each of said last mentioned connecting means comprising a resistor connected -to the respective amplifying channel, a rectifier connecting said resistor to the output side of said integrating network, and a rectifier shunting to` ground the junction of said resistor and said just-mentioned resistor, said last two rectiiers being similarly poled from the output side of said integrating network to ground.

3. In a stereophonic amplier for playing program sources of different inherent loudness and having two amplifying sound channels, the combination comprising two volume control networks having connections with said respective channels to vary controllably the volume of electronic music signals which are transmitted through said respective channels, each of said volume control networks including circuitry that is responsive to a variable control voltage applied thereto to effect as a function of the applied control voltage a controlled modication of the loudness of all the electronic music signals passing through the corresponding channel; a voltage integrating network including a choke resistor having an input side and an output side, a first ballast capacitor connected between the input side of said choke resistor and ground, and a second ballast capacitor and a bleed resistor connected in parallel between the output side of said choke resistor and ground; a pair of rectifier means `connecting the input side of said choke resistor to said respective sound channels to maintain the independence of said channels and at the same time transmit -to the input side of said choke resistor a voltage which is a function of the loudness of the louder of the two sound signals in said channels, and means connecting the output side of said choke resistor to Isaid respective control networks to elfect control of said control networks in accordance with the voltage on the output side of said choke resistor.

' References Cited in the iile of this patent UNITED STATES PATENTS 2,249,606 Friebus July 15, 1941 2,336,880 Mitchell Dec. 14, 1943 2,536,664 Sinnett Ian. 2, 1951 2,703,825 MacDonald Mar. 8, 1955 2,714,633 Fine Aug. 2, 1955 2,799,735 Breckman et al July 16, 1957 3,077,519 Riggs et al Feb. 12, 1963

Claims

1. IN A STEREOPHONIC AMPLIFIER FOR PLAYING PROGRAM SOURCES OF DIFFERENT INHERENT LOUDNESS AND HAVING TWO AMPLIFYING SOUND CHANNELS, THE COMBINATION COMPRISING TWO VOLUME CONTROL NETWORKS HAVING CONNECTIONS WITH SAID RESPECTIVE SOUND CHANNELS TO VARY CONTROLLABLY THE VOLUME OF ELECTRONIC SOUND SIGNALS WHICH ARE TRANSMITTED THROUGH SAID RESPECTIVE CHANNELS; EACH OF SAID VOLUME CONTROL NETWORKS INCLUDING CIRCUITRY THAT IS RESPONSIVE TO A VARIABLE CONTROL VOLTAGE APPLIED THERETO TO EFFECT A CONTROLLED MODIFICATION OF THE LOUDNESS OF THE SOUND SIGNALS PASSING THROUGH THE CORRESPONDING CHANNEL, WHICH MODIFICATION IS SUBSTANTIALLY UNIFORM IN DEGREE FOR ALL SOUND SIGNALS PASSING THROUGH THE ASSOCIATED CHANNEL AND WHICH IS A FUNCTION OF THE CONTROL VOLTAGE APPLIED TO THE VOLUME CONTROL NETWORK; A VOLTAGE INTEGRATING NETWORK HAVING AN INPUT SIDE AND AN OUTPUT SIDE AND INCLUDING CIRCUITRY WHICH RESPONDS TO THE APPLICATION OF A VARIABLE VOLTAGE TO THE INPUT SIDE OF THE INTEGRATING NETWORK TO PRODUCE AN OUTPUT VOLTAGE WHICH IS A FUNCTION OF THE VOLTAGE, AVERAGED OVER A PERIOD OF TIME THAT IS SUFFICIENTLY LONG TO ENCOMPASS THE PLAYING OF A NUMBER OF MUSICAL NOTES OF NORMAL DURATION, THAT IS APPLIED TO THE INPUT SIDE OF THE INTEGRATING NETWORK; MEANS INCLUDING TWO RECTIFIERS CONNECTING THE INPUT SIDE OF SAID VOLTAGE INTEGRATING NETWORK TO SAID RESPECTIVE SOUND CHANNELS AHEAD OF THE CONNECTIONS WITH THE SOUND CHANNELS OF SAID RESPECTIVE CONTROL NETWORKS TO MAINTAIN THE INDEPENDENCE OF SAID CHANNELS AND AT THE SAME TIME APPLY TO THE INPUT SIDE OF SAID INTEGRATING NETWORK A VOLTAGE WHICH IS A FUNCTION OF THE LOUDNESS OF THE LOUDER OF THE TWO SOUND SIGNALS IN SAID CHANNELS, AND MEANS INCLUDING TWO RECTIFIERS CONNECTING THE OUTPUT SIDE OF SAID INTEGRATING NETWORK IN CONTROLLING RELATION TO SAID RESPECTIVE CONTROL NETWORKS.