US2855460A - Control device for audio reproducing systems including a cross-over network - Google Patents

Description

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Oct. 7, 1958 CONTRO NORMAN INVENTORS R. THRESHER ERNEST H.F|DELLOW United States Patent 0 CONTROL DEVICE FOR AUDIO REPRODUCING SYSTEMS INCLUDING A CROSS-OVER NET- WORK Norman R. Thresher and Ernest H. Fidellow,

Our invention is an electronic device designed primarily for use in association with conventional audio reproducing equipment including a signal receiving system. and a system for converting said signal into acoustical energy. Its primary object is. to so control the audio output of the associated equipment as to automatically exclude speech from its loudspeaker, admitting to audibility only the musical portions of broadcast programs or other signal sources.

To accomplish our purpose, the A.-F. signal is tapped off some convenient point in the associated system and inserted into the circuitry of our invention. From this input signal is developed a combination of D.-C. control voltages the net effective resultant of which is characteristically different when developed from speech signals than when developed from music signals. If said circuitry determines the inserted A.-F. signal to be speech, it is intercepted at some point in the audio system before it can be converted into acoustical energy; but if the determination be that the inserted signal be music, it is permitted to complete its course unimpeded, to energize the loud speaker voice coil and become audible.

The development of the discriminating control voltages in our invention is founded on the principle that, when a full spectrum of inserted audio frequencies is divided at an appropriate frequency, the ratio of upper-frequency energy to lower-frequency energy is greater in the case of music signals than in the case of speech signals. Therefore, the energy represented by the resulting ratio-differential may be effectively applied to discriminate between speech and music signals, respectively.

Upon devision at an appropriate frequency-level, speech signals develop an appreciably lower upper-frequency to lower-frequency energy-ratio than do the great preponderance of music signals, when the latter are subjected to a corresponding frequency-division, because r speech signals are largely confined to the lower frequencies insofar as energy-development is concerned; whereas music signals are comparatively fuller in spectrum, containing fundamentals much higher in frequency and richer. in harmonic content. Thus, if 400 C. P. S. be taken as an appropriate reference frequency, the energy which speech develops in the band above 400 C. P. S. as compared with that developed in the band below 400 C. P. S. is found to be unity or less, which is appreciably smaller than the corresponding ratio in the case of a representative music signal.

Application of the general principle above stated may be conveniently illustrated. If, by some appropriate means, a full A.-F. spectrum were to be divided about some reference frequency, as 400 C. P. 8., so that its lowerfrequency band were rectified to a positive DC. voltage, and the upper-frequency band of the. same signal were simultaneously rectified to a negative D.-C. voltage; and if these two components were to bemixed across a common load; a degree of" self-cancellation ofthe original signal would take place. A D.-C. potentialwould result, bearing a polarity and magnitude each dependingon the :fxat relative magnitudes of the two rectified components, which in turn are dependent upon the frequency-content of the A.-F. spectrum originally inserted.

The foregoing application of the general principle is utilized in the circuitry of one manifestation of our. invention, as will be detailed in the disclosure to follow. Therein, D.-C. voltages are developed whose net effective result is to convert inserted speech signals into a largely positive D.-C. control voltage, whereas music signals are converted into an exclusively negative D.-C. control voltage. Said discriminatory control voltage is applied to dietate the acoustical output of the associated equipment accordingly.

Furtherobjects of our invention include a reverse operation, wherein music signals are suppressed and speech signals alone are admitted to audibility. Such an arrangement is practical in certain applications, as where our system is employed by advertising agencies for monitoring the commercial announcements of their accounts, the receiver being muted during intervening musical selections.

A further object of our invention is to provide a system whereby musical portions of programs are reproduced at normal volume-levels, whereas the speech portions are pre-adjustably subdued in volume-level, as for uses in lounges, restaurants, or wherever background music may be desired without total suppression of the speech portions of programs. This application may become important as civilian defense activities should increase. Further, it affords a means whereby announcements may be monitored for news items, musical titles, and bulletins of possible import to the listeners, yet without obtrusion of the speech signals upon those who choose to ignore them. The accent may be reversed, emphasizing the speech portions while subduing the musical portions of speciallyprepared program material, as for use in shopping centers where stress on commercial announcements is desired.

An incidental function which our invention is capable of performing is to distinguish between a signal lying within an upper-frequency band and one falling within a lower-frequency band as means for variously operating a relay or similar device to respond accordingly. Alowpitched buzzer and a high-pitched bell at the rear and front door, respectively, of a dwelling might also be made to serve as signals to illuminate the particular entrance area at whichthe caller is ringing. The application may be directed to the opening and closing of garage doors at the sound of horns, to throw power switches upon detection of malfunctioning of industrial machinery, and the like.

The accompanying drawing illustrates one specific, convenient and economical mode for applying the concept and principles underlying our invention, special reference being had to a contraphase amplifier stage.

A contraphase amplifier is a descriptive term herein adopted for convenience of expression. It is used herein to denote a conventional electron tube functioning to divide an inserted A.-F. spectrum into an upper-frequency and a lower-frequency band, respectively, said division being a function of partialdegenerative currentfeedback. From said contraphase amplifier 1, two outputs in opposite phase are taken, from its cathode and plate, respectively, in a form of phase-splitter, said outputs being utilized to produce. contrary action in supplemental circuitry. The contraphase. amplifier differs from a conventional paraphase amplifier in that its respective outputs are neither of identical frequency-composition, symmetrical phase-relationship, nor necessarily of equal amplitude, as will be more fully disclosed, post.

The A.-F. signal representing the incoming program material is inserted into the circuitry of our invention between grid-and ground ofcontraphase amplifier tube 1.

A preliminary stage of voltage amplification may in some cases be necessary. The load on contraphase tube 1 is divided between plate load resistor 2 and cathode resistor 4. Cathode resistor 4 is shunted with cathode bypass capacitor 5, the latter being inordinately small in value as compared with normal design values in this application. Its precise value is selected with reference to associated'design values so that frequencies above approximately 400 C. P. S. are adequately bypassed in the cathode circuit. Inverse feedback is therefore obtained as to the unbypassed frequencies, degeneration being confined to the band below 400 C. P. S. A signal variation on the grid of tube 1 produces a plate-current variation through cathode resistor 4, but only in response to signals falling within the lower-frequency band, below 400 C. P. S. Said plate-current variation follows the grid, thereby reducing the effectiveness of the input signal in said lower-frequency band. Dual purposes are thereby served. By selecting appropriate amplitude reference-levels, the output across partially-bypassed cathode resistor 4 is limited to a lower-frequency band, below 400 C. P. S.; and, the plate output of tube 1 is limited to the complementary upper-frequency band of the inserted signal spectrum, above 400 C. P. S.

Contraphase tube 1 may be any general purpose triode with an indirectly heated cathode, but preferably a highmu triode with high transconductance. Appropriate modifications may be made in its cathode circuit, if necessary, either to increase or decrease its operating bias voltage. Unlike the case of a paraphase amplifier, wherein identical frequency-composition of the respective outputs is important for push-pull operation, no consideration need be given to the capacitance between the filament and cathode of contraphase tube 1.

As suggested, the fequency-division between the two outputs of contraphase tube 1 is made at approximately 400 C. P. S., which closely corresponds to middle A-fiat on the musical scale. 50% of speech energy is developed by frequencies in the band below 400 C. I. S. Cathode bypass capacitor 5 is selected just small enough in value to confine degeneration to the band below 400 C. P. S. To aid the sharpness of this frequency-division, plate coupling capacitor 3 is selected small enough in value to offer high reactance to frequencies below 400 C. P. S. Cathode coupling capacitor 6 is made large enough in value to readily pass frequencies down toward the bottom of the energy-producing range of speech, to about 150 C. P. 8., yet not so low as to allow musical bass notes to produce appreciable output from the quasicathode follower of tube 1.

The respective A.-F. outputs from the cathode and plate of tube 1 are opposite in phase and, as the drawing indicates, appear across resistors 7 and 8, respectively. Said resistances 7 and 8 may be represented by the complementary sections of one potentiometer, in practice, to facilitate adjustment of the relative impedances in the diode circuits of rectifiers 10 and 11, respectively.

Each output of tube 1 is rectified to a pulsating D.-C. voltage; the plate output, representing the energy produced by signals in the upper-frequency band, being rectified by diode 10 to a negative D.-C. voltage which appears across common load 9; the cathode-follower output, representing the energy produced by signals of the lower-frequency band of the same inserted spectrum, being simultaneously rectified by diode 11 to produce an opposing positive D.-C. potential across common load 9.

While the drawing shows the net effective resultant of the two D.-C. voltage components as a single resultant D.-C. control voltage across common load 9, (for eventual application to the grid of a relay-control tube or similar device), said dual. D.-C. voltage components may be independently preserved, in any combination of polarities, for separate application to equivalent control circuitry. The latter may include the driving of two independent relay-control tube grids; or the impression of one D.-C. voltage on a control grid, while introducing the other D.-C. voltage into cathode circuitry to have opposing effect on the biasing of the same tube; or other means for producing from the two D.-C. voltage components a similar net effective result.

With reference to the specific circuit of the drawing, the resultant D.-C. voltage across common load 9, after rectification, may be either positive or negative in polarity, depending upon the relative magnitudes of the two rectified component voltages forming across said common load 9. The latter voltages, in turn, are dependent upon the relative amplitudes of the A.-F. signal voltages across resistances 7 and 8, respectively. Since the last-mentioned resistances may actually be the complementary portions of the same potentiometer in practice, the relative amplitudes of the two A.-F. signal voltages which supply rectifiers 10 and 11 may be controlled by setting such potentiometers 7-8. Such arrangement, consequently, also would provide a convenient means for controlling the relative magnitudes of the two rectified components across common load 9.

The net resultant -D.-C. control voltage thus developed across common load 9 is effective in the present applica tion (i. e., to discriminate between inserted speech and music signals, respectively), because of the lower upperfrequency to lower-frequency ratio of energy in speech signals than in music signals, as hereinbefore detailed. Because of this differential in energy-ratios, speech provides greater cancellation of its own negative D.-C. component across common load 9 than does music. In fact, when said ratio falls below unity, as it does in the case of speech signals only, the net resultant D.-C. control voltage is actually positive. Music signals, on the contrary, develop across common load 9 a resultant D.-C. voltage negative in polarity, and greater in magnitude than speech signals are capable of there developing in the negative direction.

Though the use of a single contraphase amplifier stage 1 for producing both of the split-frequency band outputs, aforementioned, is attractive from the standpoints of design-simplicity and construction-economy, its use necessarily cooperates with the remainder of the circuitry of our invention in its development of a definitive discriminating control voltage. The reason resides in phase differences concomitant to splitting a frequency spectrum through the medium of a single electron tube, as in the manner hereinbefore disclosed. In the case of inserted speech signals, the plate (upper-frequency band) output of contraphase tube 1, which ultimately produces a negative D.-C. voltage component across common load 9, (and which should be kept to a minimum during speech signals for effective discrimination), is almost exclusively produced by harmonics. Speech harmonics, therefore, are out of phase with their fundamentals, since the latter lie within the range of the cathode-follower (lowerfrequency) output. On the other hand, the fundamentals of a high proportion of music signals fall, along with their harmonics, within the upper-frequency band (above middle A-fiat, for example), which yields the plate output of tube 1. Said music fundamentals are consequently in phase with the harmonics they produce. The advantage in having speech harmonics be 180 out of phase with their fundamentals, while a high percentage of music harmonics are in phase with their fundamentals, may be gathered from the following data.

During the positive half-cycle of a speech fundamental, its harmonics contribute nothing to the magnitude of the negative D.-C. component across common load 9. During its negative half-cycle, even harmonics develop some magnitude of negative component during 50% of the time-duration of said fundamental tone, but the odd harmonics contribute to said negative component only 33-40% of the time-duration of the fundamental. On the other hand, that high proportion of music fundamentals which produce harmonics in phase with themselves,

both forming part of the plate (upper-frequency) output of contraphase tube 1, contribute more generously to the magnitude of the negative D.-C. voltage component across common load 9. For example, a negative D.-C. voltage component is being fed to common load 9 during 100% of the negative half-cycle of a music fundamental lying within the upper-frequency range, with the harmonic voltage content being additive 50-67% of that time for all orders of harmonics. Thus, the phase-opposition between the cathode and plate outputs of contraphase tube 1, respectively, redounds to the advantage of music signals in their mission of developing a higher magnitude of negative D.-C. control voltage across common load 9 than speech signals are able to there develop.

The net eifective resultant of the respective outputs of the two diodes 10 and 11, which is shown in the circuitry of the drawing as a single resultant D.-C. voltage across common load 9, and which discriminates between inserted speech and music signals, respectively, may be applied in various ways to control the acoustical output of the associated equipment accordingly. One means for accomplishing this is shown in the drawing, wherein said resultant D.-C. control voltage is applied to drive grid 16a of relay-control tube 16. Instead of applying said control voltage directly to grid 16a, an RC network 121314 is interposed between said grid 16a and common load 9. The latter network is, basically, anordinary series time-delay comprised of resistor 13 and capacitor 14. Said delay network enhances the efiiciency of operation of our circuit in that it serves to dampen the relatively high instantaneous peak voltages developed in the upper-frequency range by speech signals upon occasion, especially upon over-emphasis of words, throat-clearing, and the like. The RC constant of network 1314 might, in practice, be of the order of 500-1000 millielement 13. Capacitor 12 is selected of such value as to offer high reactance to D.-C. pulsations in the effective energy-producing speech range, or up to approximately 3000 C. P. S.; and to offer progressively lower reactance to D.-C. pulsations of higher frequencies, which latter are produced exclusively by music signals. Thus, time-delay network 13-14 is fully operative in the circuit of our invention for all frequencies up through the effective energyproducing speech range, but becomes progressively less elfective in impeding pulsations of higher frequencies. Therefore, a single flute note, for example, even though of very short duration, may quickly develop a negative D.-C. pulse on grid 16a of relay control tube 16, thus aiding to a more material degree other musicsignals in their function of blocking said tube 16.

Capacitor 12, further, has a grid-leak biasing effect, when the resultant D.-C. voltage across common load 9 is positive in polarity, since current then flows in the grid circuit of relay-controltube 16. Through the greatly diminished cathode-to-grid resistance of tube 16,at such times, capacitor 12 quickly charges up to essentially the full value of said positive control voltage and results in grid 16a, which is connected to the low potential plat of capacitor 12, being held essentially at cathode potential. This grid-leak action limits the positive swing of control grid 16a, thereby adding to the life of tube 16. The attendant reduction in effectiveness of a positive D.-C. control voltage on grid 16a is of negligible importance to the desired operation of our circuit.

Therefore, the resultant D.-C. control voltage which is developed across common load 9, and which-discriminates between speech and music, respectively, is applied 6 through variable delay network 1213l4 to grid 16a of relay-control tube .16. Control .tube 16 is so biased by the potential developed across its cathode resistor 15 (which may in practice be made variable for convenience in adjustment) that the plate current through said tube 16, in the quiescent state, is just sufficient to .energize relay coil 17, thereby opening relay switch 17a. The latter action opens voice coil circuit line 18, or more practically, as shown in the drawing, introduces into voice coil circuit line 18 a power-absorbing impedance 19. Before any inserted A.-F. signal can thereafter become audible, switch'17a must again be closed, thereby again shorting out impedance 19. To accomplish this, a certain magnitude of negative D.-C. voltage is required to be impressed upon grid 16a of relay-control tube 16, to so alter its bias that the plate current through said tube 16 is reduced to the point where relay solenoid 17 is again deenergized, thereby returning switch 17a to its normally-closed position. Said D.-C. control voltage for impression upon grid 16a is developed in the circuitry of our invention across common load 9, as hereinbefore detailed.

Upon the insertion into our circuitry of A.-F. signals comprised of speech, the control voltage developed across common load 9 is positive in-polarity; or, when negative, it fails to attain such magnitude that, when applied to grid 16a of relay-control tube '16, the latters plate current would be sufficiently reduced to deenergize relay coil.17. Therefore, upon speech signals, the quiescent state persists, in which voice coil circuit linelS remains impeded, said speech signals being therefore inaudible.

On the contrary, inserted music signals develop a negative D.-C. control voltage across common load 9 of our circuitry, said negative D.-C. control voltage being sulficient in magnitude that, when impressed upon grid 16a of relay-control tube 16, it decreases the latters plate current sufiiciently to deenergize relay coil 17, thereby returning switch 17a to its normally-closed position. The latter action shunts abnormal impedance 19, which restores the voice coil circuit line 18 to its normal condition, thus permitting the energization of the voice coil by said inserted music signals.

Circuit refinements may of course be made, according to the collateral objects desired to be accomplished by our invention, or to elaborate upon the simple circuit as shown in the drawing for increased operating efficiency. Some brief examples follow.

To limit the loss of upper-frequency energy into the circuit of lower diode 11, the latter may be isolated from the circuitry of diode 10 by the insertion of an inductance between point 9a and the cathode of rectifier 11, reference being had to the accompanying drawing. The added choke should have a low D.-C. resistance, and should offer high inductive reactance to the pulsating D.-C. output of diode 10.

A capacitor may be added in shunt with resistor 7 to aid in the appropriate frequency-division of inserted program material into an upper-frequency and a lower-frequency band, respectively.

A normally-open relay switch may be substituted for normally-closed switch 17a shown in the drawing. Thereby music may be expunged from broadcast programs, while speech signals alone are reproduced. Or, by employment of a spdt switch in that position, a manually-operated toggle switch may be provided on the control panel of our device for selecting one mode of operation or the other, depending upon whether the normally-open or the normally-closed side of said spdt relay switch is thereby cut into the voice coil circuit line 18.

Further, a multiplicity of switches may be added to the relay to perform such functions as feeding one type of signal to a monitor speaker or secondary line of speakers, while the other type of signal is made to energize a network of principal speakers; or, to shunt the secondary winding of the associated audio output transformer 20 7 with a dummy resistive load in substitution for the associated voice coil when the latter is disconnected, for the better protection of said transformer 20; etc.

A vacuum tube relay circuit, or other completely electronic circuit, may be arranged in substitution for the mechanical relay device shown in the circuit of the accompanying drawing.

The power-absorbing impedance 19 may be made variable, for manually pre-setting the degree of suppression of the program material deemed to be of secondary importance in the particular application, whether said material be speech or music.

Other circuit refinements and adaptations will suggest themselves to designers of electronic equipment. The textual matter of the above disclosure is presented in elucidation of our basic conception, and nothing therein is intended as a specific limitation on the practical application thereof.

We claim:

I. Adjunctive to an associated system including a radio receiver or other signal device responsive to A.-F. signals with an audio amplifier and sound-reproducer, a selective electronic circuit connected to said amplifier through means limiting the peak energy of received signals, including means for establishing a reference-frequency, means for dividing the A.-F. content of a received signal about said reference-frequency effectively into a higherfrequency band and a lower-frequency band relative to said reference-frequency, means for averaging the respective energy-contents of said respective frequencybands, means for distinguishing between respective signals whose average energy lies preponderately in said higher-frequency band and preponderately in said lowerfrequency band, with further means for permitting or impeding the activation of the associated sound-reproducer by said received signal according to the type of signal as hereinbefore distinguished by said adjunctive circuit.

2. Adjunctive to an associated system including a radio receiver or other signal device responsive to A.-F. signals with an audio amplifier and sound-reproducer, a selective electronic circuit connected to said amplifier through means limiting the peak energy of received signals, including means for establishing a reference-frequency, means for dividing the A.-F. content of a received signal about said reference-frequency effectively into a higher-frequency band and a lower-frequency band relative to said reference-frequency, means for independently rectifying the energy of said respective frequency-bands into D.-C. voltages of mutually-opposing polarities, means for composing said respective D.-C. voltages into one resultant D.-C. control voltage bearing the polarity of its dominant D.-C. voltage component and equalling in magnitude the absolute voltage-differential existing between said respective component voltages, means operative upon excitation by a predetermined minimum value of said absolute voltage-differential of that polarity developed by the energy of said higher-frequency band, and a relay connected to the last mentioned means, said relay operating to select between activation and suppression of said associated sound-reproducer upon operation of said last mentioned means.

3. Adjunctive to an associated system including a radio receiver or other signal device responsive to music and speech signals with an audio amplifier and sound-reproducer, a selective electronic circuit discriminatory between received music and speech signals connected to said amplifier through means limiting the peak energy of received signals, including means for dividing the A.-F. content of a received signal comprising music or speech about a preselected reference-frequency effectively into a higher-frequency band and a lower-frequency band relative to said reference-frequency, means for averaging the respective energy-contents of said frequency-bands, means for establishing said reference-frequency at such appropriate frequency that the average energy of representative music signals falls predominantly in said higherfrequency band while conversely the average energy of representative speech signals falls predominantly in said lower-frequency band, means for distinguishing between respective received signals whose average energy lies preponderately in said higher-frequency band, as in music signals, and preponderately in said lower-frequency band, as in speech signals, with further means for permitting or impeding the activation of the associated sound-reproducer by the received signal according to whether said electronic circuit thus determines said signal to be music or speech, respectively.

4. A selective electronic circuit excited by a signal inserted from an external source through means limiting the peak energy of said signal, with means for establish ing a reference-frequency, means for dividing the frequency-content of said inserted signal about said reference-frequency effectively into a higher-frequency band and a lower-frequency band relative to said referencefrequency, means for independently rectifying and averaging the respective energy-contents of said frequencybands into D.-C. voltages of mutually-opposing polarities, means for composing said respective D.-C. voltages into one resultant DC. control voltage bearing the polarity of its dominant D.-C. voltage component and equalling in magnitude the absolute voltage-ditferential existing between said respective component D.-C. voltages, and means for applying said resultant D.-C. control voltage to control the operation of a relay according to the polarity and magnitude of said resultant voltage.

5. A selective electronic circuit excited by a signal inserted from an external source through means for limiting the peak energy of said signal, with means for establishing a reference-frequency, means for dividing the frequency-content of said inserted signal about said reference-frequency effectively into a higher-frequency band and a lower-frequency band relative to said reference-frequency, means for independently rectifying and averaging the respective energy-contents of said frequencybands into D.-C. voltages of mutually-opposing polarities, and means for applying said respective D.-C. voltages in combination to control the operation of a mechanism according to the respective polarities and magnitudes of said D.-C. voltages.

6. Adjunctive to an associated system including a radio receiver or other signal device responsive to music and speech signals with an audio amplifier and sound-reproducer, a selective electronic circuit connected to said amplifier through means limiting the peak energy of received signals, including means for dividing a received A.-F. spectrum comprising music or speech about a preselected reference-frequency effectively into a higherfrequency band a lower-frequency band relative to said reference-frequency, means for independently rectifying the energy of said respective frequency-bands into D.-C. voltages of mutually-opposing polarities, means for composing and averaging said respective D.-C. voltages into one resultant D.-C. control voltage bearing the polarity of that aforesaid component voltage dominant in average energy, means for establishing said reference-frequency at such appropriate frequency that, relative thereto, said division of music signals alone can produce a ratio of higher-frequency to lower-frequency average energy exceeding unity and a consequent resulting D.-C. control voltage opposite in polarity to that resulting from a corresponding division of speech signals, said electronic circuit including further means for applying said resultant D.-C. control voltage to control the operation of a relay according to the polarity of said resultant D.-C. control voltage, said relay correspondingly controlling the acoustic output of said associated sound-reproducer.

7. Adjunctiveto an associated system including a radio receiver or other signal device responsive to music and speech signals With an audio amplifier and sound-reproducer, a selective electronic circuit connected to said amplifier through means limiting the peak energy of re ceived signals, including means for dividing a received A.F. spectrum comprising music or speech about a preselected reference-frequency effectively into a higherfrequency band and a lower-frequency band relative to said reference-frequency, means for independently rectifying the energy-contents of said respective frequencybands into D.-C. voltages of mutually-opposing polarities, means for composing and averaging said respective D.-C. voltages into one resultant D.-C. control voltage bearing the polarity of that aforesaid component D.-C. voltage dominant in average energy and equalling in magnitude the absolute voltage-differential existing between said respective component D.-C. voltages, means for establishing said reference-frequency at such appropriate frequency that, relative thereto, said division of music signals produces a ratio of higher-frequency to lower-frequency average energy sufficiently greater than that producible by a corresponding division of speech signals to consequently develop in the polarity of said rectified higherfrequency energy a resultant D.-C. control voltage of a magnitude unattainable by speech signals, said electronic circuit including further means for applying said resultant D.-C. control voltage to control the operation of a relay according to the magnitude and polarity of said resultant voltage, said relay correspondingly controlling the acoustic output of said associated soundreproducer.

8. Adjunctive to an associated system including a radio receiver or other signal device responsive to A.-F. signals with an audio amplifier and sound-reproducer, a selective electronic circuit including a cathode-biased electron tube with a received A.-F. spectrum collaterally impressed on its grid by the said associated amplifier through means limiting the peak energy of received signals, with loading means for realizing a dual output respectively from the plate and cathode of said electron tube, means for establishing a reference-frequency, means for degenerating in the plate output of said electron tube audio frequencies below said reference frequency, means for degenerating in the cathode output of said electron tubeaudio frequencies above said reference-frequency, means for independently rectifying the energy of said respective outputs of said electron tube into D.-C. voltages of mutually-opposing polarities, means for composing and averaging said respective D.- C. voltages into one resultant D.-C. control voltage bearing the polarity of its dominant DC. voltage component and equalling in magnitude the absolute voltage-differential existing between said respective component D.-C. voltages, and means for applying said resultant D.-C. control voltage to control the operation of a relay according to the polarity and magnitude of said resultant control voltage, said relay correspondingly controlling the acoustic output of said associated soundreproducer.

9. In an electronic circuit with means for dividing the frequency-content of an inserted signal about a predetermined reference-frequency into a higher-frequency band 60 and a lower-frequency band relative to said referencefrequency, with means for independently rectifying and averaging the respective energy-contents of said frequencybands, and with means for controlling a mechanism according to the resulting ratio of average higher-frequency energy to lower-frequency energy, manually-operated means for variably regulating said ratio producible from a given inserted signal, said latter means operating to 10 vary the relative impedance in said respective rectifying circuits.

10. In an electronic circuit with means operating to control a mechanism according to the distribution of the total energy of an inserted signal frequency-spectrum respectively between its higher-frequencies and its lowerfrequencies relative to a predetermined reference-fire quency, means for dividing the energy of said inserted frequency-spectrum about said reference-frequency, said latter means including a cathode-biased electron tube with said inserted signal impressed on its grid, a capacitor shunting the cathode-biasing resistor of said electron tube, said capacitor being of such inordinately small capacitance to produce degenerative current feedback in the stage of said electron tube as to said lower-frequencies of the inserted signal but not sufiiciently small in capacitance to prevent ad-equate frequency-bypassing of said higher-frequencies of said signal, means for developing in the plate circuit of said electron tube from the undegenerated higher-frequencies of an inserted signal an output substantially equal in energy to an output simultaneously developed in the cathode circuit of said tube from the inadequately-bypassed lower-frequencies of the same inserted signal when said signal is at said reference-frequency, means coupling said plate output to its load offering progressively less impedance to frequencies above said reference-frequency, and means coupling said cathode output to its load offering progressively less impedance to frequencies below reference.

11. Means for dividing the contents of a frequencyspectrum about a predetermined reference-frequency cf fectively into two bands complementary in frequencycontent, said bands respectively comprising a higherfrequency band and a lower-frequency band relative to said reference-frequency, said means including a cathodebiased electron tube, means for dividing the load on said tube between its plate and cathode circuitry to produce substantially equal loading on each said respective circuit upon impression on the grid of said electron tube of a signal at said reference-frequency, a network in the cathode circuit of said tube of such component values as to be progressively more discriminatory against frequencies higher than said reference-frequency and operative to produce progressively increasing degenerative current feedback in the stage of said tube upon impression of signals at frequencies below said reference-frequency, said cathode network being further operative to variably bias said tube according to the frequency of the impressed signal, loading means for realizing an output from the plate of said tube comprising the undegenerated frequencies of said higher-frequency band, loading means for realizing an output from the cathode circuit of said tube comprising the frequencies of said lower-frequency band inadequately bypassed in said cathode network, means coupling said plate output to its said loading means progressively more discriminatory against frequencies below reference, "and means coupling said cathode output to its said loading means progressively more discriminatory against frequencies above reference.

References Cited in the file of this patent UNITED STATES PATENTS Re. 21,151 Adair July 18, 1939 2,089,637 Adair Aug. 10, 1937 2,250,596 Mountjoy July 29, 1941 2,424,216 Atkins July 22, 1947 2,575,109 Howes Nov. 13, 1951

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