US3798373A - Apparatus for reproducing quadraphonic sound - Google Patents

Apparatus for reproducing quadraphonic sound Download PDF

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US3798373A
US3798373A US00155976A US3798373DA US3798373A US 3798373 A US3798373 A US 3798373A US 00155976 A US00155976 A US 00155976A US 3798373D A US3798373D A US 3798373DA US 3798373 A US3798373 A US 3798373A
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signals
signal
composite
auxiliary
amplitude
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B Bauer
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CBS Broadcasting Inc
Sony Music Holdings Inc
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Columbia Broadcasting System Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S3/00—Systems employing more than two channels, e.g. quadraphonic
    • H04S3/02—Systems employing more than two channels, e.g. quadraphonic of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other

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  • ABSTRACT Apparatus for decoding four separate channels of information transduced from a medium having only two separate tracks and presenting it on four loudspeakers to give the listener the illusion of sound coming from a corresponding number of separate sources.
  • the realism is enhanced by a decoding system which accepts the two outputs from the medium, which may be a stereophonic disc record, separates them into four independent channels each carrying predominantly the information contained in the four original recorded sound signals, and, utilizing a wave-matching technique derives control signals for controlling the gains of amplifiers associated with the four loudspeakers.
  • the control circuitry improves the separation of the four independent channels, particularly the generally front from the generally back" signals.
  • the front-to-back separation is improved by intermixing some of the left output signal into the right output signal, and vice versa, at both the front and the back sets of decoder output terminals.
  • This invention relates to systems for recording and reproducing four separate channels of information on a medium having only two independent tracks, and more particularly to apparatus for reproducing such information and presenting it on four loudspeakers to give the listener the illusion of sound coming from a corresponding number of separate sources. More particularly, the present invention is concerned with a decoder for improving the realism of sound decoded from a matrixed quadraphonic record, recorded on a twotrack medium in accordance with the method described in aforementioned copending application Ser. No. 124,135 and similar systems.
  • a quadraphonic encoder for this purpose is illustrated in FIG. 8 of the aforementioned application Ser. No. 124,135, but it is to be understood that the decoder to be descried herein is operative to reproduce signals encoded with encoders of other configurations, for example, the encoder described in co-pending application Ser. No. 384,334.
  • the encoder produces two composite signals that can be recorded on a two-track medium, such as magnetic tape or a disc record, utilizing conventional recording techniques.
  • the two output channels which for convenience will hereinafter be designated R and L (for total or transmitted left and right signal, respectively) may be recovered from a phonograph record with a conventional phonograph pickup, or alternatively, transmitted directly from the encoder, and applied to a decoder which transforms them into four new signals, predominant components of which correspond to the original signals L L R; and R applied to the encoder, except that they may have a different phase orientation than the original signals.
  • An essential feature of the decoder is a combination of all-pass phase-shifting networks, usually employed in groups of two or more, for positioning the components of the two composite signals to permit combination thereof by addition and subtraction.
  • Each network of a group has a basic phase-shift angle, 1', which is a function of frequency, and an incremental angle, A, which is essentially constant over the frequency range of interest.
  • the angle A is normally zero to although it will be evident from the description to follow that other values may be used with equivalent es a
  • the nature of the encoded signals, and the signifi cance of the phase-shifting networks will be better understood from a brief description of the encoder illustrated in FIG. 8 of the aforementioned application Ser. No. 124,135, which is repeated herein as FIG. 1.
  • the encoder has four input terminals 10, 12, 14 and 16 to which four input signals L,, L,,, R, and R depicted as in-phase signals of equal amplitude, are respectively applied.
  • the total L, signal is added in a summing junction 18 to 0.707 of the R signal, the output of this summing junction being applied to a phase-shifting network 20 which introduces a reference phase-shift I which, as was noted earilier, is a function of frequency.
  • the full R, signal at terminal 16 is added in summing network 22 to .707 of the L signal appearing at input terminal 12, and the output passed through the ill-network 24, which also provides the reference phase-shift '11.
  • the L,, and R signals are also applied to respective ill-networks 26 and 28, each of which provides a phase shift of 111 90.
  • the angular notation used refers to lagging angles, but as long as there is consistency in notation, it makes no difference to the operation of the system whether the angles are lagging or leading.
  • the full signal appearing at the output of network 20 is added in a summing circuit 30 to 0.707 of the signal appearing at the output of network 26 to produce at its output terminal 32 a composite signal designated L
  • the full signal from network 24 is added in summing junction 34 to 0.707 of the signal from network 28, the latter in this case being in the positive sense.
  • the signal appearing at the output terminal 36 is the composite signal R
  • the signals L and R may be recorded on any two-channel medium such as a two-track tape or stereophonic record for later reproduction, or may be transmitted by FM multiplex radio.
  • the composite signals appearing at output terminals 32 and 36 are portrayed as phasor groups 38 and 40, respectively, which may be characterized in complex notation, as follows:
  • the phasor 0.707L in phasor group 40 lags behind the similarly numbered phasor in phasor group 38, and conversely, to arrange phasor 0.707R in phasor group 38 to lag behind the corresponding phasor in group 40.
  • Co-pending application Ser. No. 1 18,271 describes a system for decoding of the signals L and R depicted in FIG. 1, in which they are respectively applied to a pair of phase-shifting networks, one network of each pair introducing a phase-shift of (11 and the other network of each pair introducing a phase-shift of (w 90).
  • the two phasor groups appearing at the outputs of the LII-networks to which the L signal is applied are in quadrature relationship, as are the two phasor groups appearing at the outputs of the ill-networks to which the R signal is applied.
  • the phasors at the outputs of the four ill-networks are properly positioned for selective addition and subtraction to derive four separate output signals predominantly containing the original signals L L R and R respectively, for reproduction over four corresponding loudspeakers.
  • These decoded signals are not pure or discrete original signals, however, each being diluted" by two other signals. Nevertheless, when all four channels of the original program contain musical signals in concert, and the four decoded signals are reproduced o ver respective loudspeakers placed in the corners of the room or listening area, then as far as the listener is concerned there is sufficient mixing of the sounds in the room that the resulting overall sound effect is quite similar to the sound of the original four discrete channels, and a credible simulation of the original four-channel program results.
  • control systems for achieving signal enhancement are described in co-pending applications Ser. Nos. 384,334 and 25 l .636. It is a primary object of the present invention to obtain greater quadraphonic realism than that attainable with previously described methods while, at the same time. simplifying the circuitry for accomplishing it.
  • the logic is designed to compare the voltages in adjacent channels and to derive control signals for reducing the gains of the output amplifiers for such channels whenever the voltages are in-phase or in quadrature phase condition, thereby to eliminate the side-effect signals. That is. the logic senses the presence of side-effect signals and causes the gains of the appropriate output am plifiers to be correspondingly increased so that the total acoustical power contributed by the active loudspeakers resmins unchanged.
  • Substantially constant amplitude signals for comparison of the voltage in adjacent channels, regardless of changes in level of the program, are obtained by applying a pair of signals derived from the decoder respectively corresponding to the composite input signal R and the composite signal L shifted by from its input phase condition, to respective gain control amplitiers which include means for maintaining the amplitude of their outputs substantially constant.
  • the output signals from these auxiliary gain control amplifiers are selectively added and subtracted to produce two additional signals, also of substantially constant amplitude, resembling two signals produced in the decoder and ultimately applied to two of the four loudspeakers.
  • the four signals thus produced are separately rectified and the resulting wave forms compared in pairs in a pair of subtracting junctions, for example, the outputs of the junctions again rectified, and one of the rectified outputs subtracted from the other two produce a signal of one polarity or the other indicative of the presence of side-effect signals.
  • Signals of one polarity control in unison the gains of the gain control amplifiers associated with the two front" loudspeakers, and signals of opposite polarity control the two back" loudspeakers in unison.
  • the ability of the logic to discriminate between generally front and generally back signals is enhanced by comparing the substantially constant amplitude signal from one of the above-described gain control amplifiers, preferably the one to which the R composite signal is applied, with the output of a third auxiliary gain control amplifier (which also has a substantially constant amplitude output) to which the L composite signal is applied.
  • the comparison is made by obtaining the sum and the difference of the two outputs, separately rectifying the sum and difference signals, and obtaining the difference of the two rectified signals. That portion of the latter difference signal which exceeds a predetermined level is added to the control signal generated by the wave-matching logic described in the preceding paragraph for application to the output gain control amplifiers.
  • the front-to-back discrimination of the decoder is enhanced, without the use of a logic and control circuit, by blending or mixing the signals in some of the output channels of the matrix decoder with signal in some of the other channels. More particularly, a fraction of the signal in the left front" channel is added to the right front" signal, and a like or different fraction of the signal in the right front” channel is muxed with the left front signal. Similarly, fractions of the signals in each of the left back and right back channels are intermixed with the full signal in the other.
  • FIG. 1 is a schematic diagram of an encoder for encoding four original sound signals into two composite signals, to which reference has already been made in discussing the background of the invention;
  • FIGS. 2A and 2B taken together is a schematic diagram of decoding apparatus embodying the invention.
  • FIG. 3 is a plot of the output of the front-back logic circuitry of the system of FIG. 2 as a function of panning a constant signal around a circle;
  • FIG. 4 is a plot of the output of the wave-matching logic of the system of FIG. 2 as a function of panning" a constant signal throughout a circle;
  • FIG. 5 is a plot of the values of the phasors for the four channels as a function of the bearing angle for eight positions of a panned signal.
  • FIG. 6 is a series of phasor diagrams useful in explaining the operation of the channel intermixing feature of the decoder of FIG. 2.
  • the decoder of the present invention is similar in many respects to the decoder described in aforementioned application Ser. No. 384,334 certain details of which, in turn, are described in application Ser. No. 118,271.
  • the input signals to the decoder designated L and R and depicted by the phasor groups 38 and 40, respectively, are applied to respective input terminals 42 and 44.
  • the L signal is applied in parallel to a pair of all-pass phase shifting networks 46 and 48 which introduce phase shifts of (41 0) and (ill 90). respectively, and the R signal is similarly applied to a pair of all-pass networks 50 and 52 which provide phase shifts of (d; 90) and (111 0).
  • phase-shift networks are operative to produce four signals at the output terminals or leads 54, 56, 58 and 60, depicted by the phasor groups 62, 64, 66 and 68, respectively.
  • the designations of the components of the phase-shifted signals are primed.
  • the signals appearing on conductors 56 and are each multiplied by the coefficient 0.707 and added together at a summing junction 70 to produce a new signal at the output terminal 71 thereof, while the signals on conductors 54 and 58 are multiplied by the coefficient O.707 and added together in a summing junction 72 to produce a second new signal at its output terminal 73.
  • the signals on conductors 54, 71, 73 and 60 are amplified by amplifiers 74, 76, 78 and 80, respectively. and applied to corresponding loudspeakers 82, 84, 86 and 88 where they are reproduced as sounds which correspond to the configuration of phasor groups 90, 92, 94 and 96, respectively.
  • quadraphonic realism can be improved by blending or mixing the outputs of some of the channels with the outputs of other channels before amplification.
  • This blending operation is accomplished be means of four summing junctions 98, 100, 102 and 104 each of which is operative to add the signal from one channel to a fraction of the signal of another channel. More specifically, junction 98 adds a fraction, designated n, of the signal appearing on conductor 60 to the signal appearing on conductor 54, the output of the summing junction being applied to amplifier 74. Similarly, the junction 100 adds a fraction, n, of the signal on conductor 54 to the signal on conductor 60, the sum being applied to amplifier 80. Similarly, summing junction 102 adds a fraction, designated m, of
  • the phasor groups 90, 92, 94 and 96 are, for clarity, shown for the condition where the fractions m and n are zero, that is, for a matrix without blend, and that the logic and control circuitry to be described hereinbelow, which is an extension of the control circuitry described in copending applications Ser. Nos. 118,271 and 124,135, can be used with a decoding matrix with or without blend; the effect on the corresponding phasor groups of intermixing some of the left output into the right channel and vice versa, in both the front and back sets of loudspeakers, will be described later with reference to FIG. 6, following a description of the balance of the system of FIG. 2.
  • the phasor groups 90, 92, 94 and 96 which characterize the sounds emanating from the four loudspeakers 82, 84, 86 and 88, respectively, and which are usually placed in a listening room or area so that the signals L,', L,,, R,” and R," are localized at the left front, left back, right back and right front corners, contain dominant signals L L,,, R,,' and R;; however, they each also contain diluting or side-effect signals from two other channels.
  • these side-effect signals are relatively unobjectionable in the thus far described matrix configuration, the perfection of quadraphonic sound reproduction is enhanced if the gains of those channels which contain only side-effect signals are controllably diminished.
  • the. electronic logic is operative to develop control signals for the gain control amplifiers by operating on three signals developed in the matrix of FIG. 2A, preferably the signals appearing on conductors 60, 56 and 54.
  • the signals from conductors 60, 56 and 54 are first coupled through respective, substantially identical high pass filters 110, 112 and 114 designed to reject frequencies below about SOI-Iz-frequencies which nor mally should not be involved in the logic action.
  • the transmission characteristic of the filters above the cutoff point is preferably adjusted so as to optimize the logic control action in accordance with the sensitivity of the ear to the loudness of various sounds.
  • the signals delivered by the filters are applied to the input terminals of respective gain control amplifiers 116, 118 and 120 which have identical or closely similar gain versus control voltage characteristics. It will be observed that the signals from conductors 60 and 56 applied to amplifiers 116 and 118, respectively, are obtained from the outputs of all pass phase-shift networks 52 and 48, respectively, whereby corresponding components of the R and L composite signals are shifted in phase relative to each other by 90. This phase relationship permits the signals delivered by gain control amplifiers 116 and 118 to be added and subtracted to derive two new signals having properties advantageous to the desired performance of the logic.
  • each of the signals from amplifiers 116 and 118, appearing at terminals 130 and 132, respectively, are added in a summing junction 122 to produce at its output a new signal represented by the phasor group 124, in which the component L, is predominant.
  • O.707 of the signal from amplifier 118 is added in another summing junction 126 to 0.707 of the signal from amplifier 116 to produce at its output terminal another new signal represented by the phasor group 128, in which the component R, is predominant.
  • the predominant component of the signals appearing at terminals 130 and 132 are R, and L,, respectively.
  • the four signals just described are rectified by respective rectifiers 134, 136, 138 and 140, which are preferably full-wave rectifiers, each of which includes respective time constant circuits 142, 144, 146 and 148, each designed to provide a rapid attack time, of the order of about 1 millisecond, and a relatively slower decay time, of the order of about milliseconds.
  • the four rectified signals are added together in a summing junction 150 and the sum signal is applied to the control electrodes 1 16a, 118a and 120a of gain control amplifiers 116, 118 and 120.
  • Application of the sum of the rectified signals in the illustrated feedback relationship automatically and simultaneously adjust the gains of the amplifiers in response to changes in the strength of the signals being-processed, thereby to maintain the amplitude of the rectified signals essentially constant.
  • rectifiers 134, 136, 138 and to develop the gain control signal are also applied to rectifiers 152, 154, 156 and 158, respectively, which are preferably fullwave rectifiers and the rectified outputs therefrom then subtracted in pairs in subtracting junctions 160 and 162.
  • the rectified signal appearing at terminal 132 is subtracted in junction 160 from the rectified signal appearing at terminal 130 and the rectified signal represented by phasor group 124 is subtracted in junction 162 from the rectified signal corresponding to phasor group 128.
  • rectifiers 152-458 are shown as not having resistor and capacitor time constant circuits; this is deliberate to indicate that these rectifiers desirably have a short time constant. In fact, if ideal phaseshift networks were available, no time constant elements would be required because the waves to be matched would be in perfect alignment with each other; however, because of circuit imperfections, these rectifiers may be designed to have a relatively short time constant, of the order of a fraction of a millisecond to a few milliseconds, which may, in fact, be provided by the capacitance of the circuit leads.
  • the output signals from junctions 160 and 162 are again rectified by rectifiers 164 and 166, respectively, (which preferably are also full-wave rectifiers) having associated time constant circuits 168 and 170 the resistance and capacitance values of which are selected to provide a rise time of the order of l millisecond and a decay time of the order to 20 milliseconds. It should be understood, however, that wide variations in these values may be used without substantially affecting the operation of the invention.
  • the output signal from rectifier 166 is subtracted in a subtracting junction 172 from the output signal from rectifier 164 and the difference signal appearing at its output terminal 174, which represents the contribution of the wave-matching logic to the control signals for the gain control amplifiers 74-80 in FIG. 2A, is applied as one input to a summing junction 176.
  • junction 172 For this signal condition, then, rectification of the outputs of junctions 160 and 162, and subtraction thereof in junction 172, will produce a positive signal at terminal 174.
  • Other signal conditions may result in correlation and cancellation in junction 160 so as to produce zero output therefrom, while at the same time the signals applied to junction 162 may be incoherent and thus produce an output signal, with the consequence that the output signal from junction 172 would be of negative polarity.
  • the signal delivered by junction 172 (which may be positive or negative) applied to one input of summingjunction 176 (the second input to which will be subsequently described) and the output thereof is applied in parallel to transmission elements 178 and 180.
  • Transmission element 178 is a network that is operative to transmit a control signal therethrough without change in sign and has a transfer function designed to avoid overloading the controls of the gain control amplifiers 74-80.
  • Transmission element 180 is similar to transmission element 178 except that it includes means for inverting the sense of signals applied to it. Therefore, the signals delivered by transmission element 178 and 180 in response to a given input signal are of the same magnitude but of opposite polarity.
  • the output signal from transmission element 178 is applied via conductor 179 to the control electrodes of gain control amplifiers 74 and 80, and the output of transmission element 180 is applied over conductor 181 to the gain control electrodes of amplifiers 76 and 78.
  • a positive signal appearing at the output of junction 176 passes through transmission element 178 without change of sign, and upon application to the control electrodes of amplifiers 74 and 80 increases their gains and enhances the signals L and R," emanating from loudspeakers 82 and 88, respectively.
  • the positive signal at the output of junction 176 is inverted by transmission element 180 with the consequence that when it is applied to the control electrodes of amplifiers 76 and 78, the gains thereof are decreased, thereby to attenuate the side-effect signals in their associated loudspeakers 84 and 86.
  • the gain control amplifiers 7480 preferably have time constants such as to permit relatively rapid increase in gain in response to application of positively going control signals and a relatively slow decrease in gain when the gain control signal decreases, in accordance with the teaching of applicant's aforementioned co-pending application Ser. No. 118,271.
  • the action of thepresent wave-matching logic is as described in application Ser. No. 118,271 except for the utilization of automatic gain control amplifiers 116 and 1 18 to provide signals of substantially constant amplitude for wave-matching, and the manner in which the output signal from the wave-matching logic interacts with the output of a second logic circuit for providing improved separation between front and back signals, now to be described.
  • the front-back logic utilized in the present system is similar in some respects to the front-back logic described in applicants aforementioned co-pending application Ser. No. 124,135, and the disclosure thereof is hereby incorporated by reference.
  • the signals for the front-back logic are derived from the outputs of automatic gain control amplifiers 116 and 120, one of which it will be noted is common with one of those used to derive the signals for the wave-matching logic, and which provide relatively constant level output signals corresponding to the phasor groups 68 and 62, respectively.
  • L, and R signals in these two phasor groups are in phase with the consequence that if a front center signal is applied to the L, and R, terminals of the encoder of FIG.
  • the output signals from gain control amplifiers 116 and 120 are applied to the two inputs of an adding junction 190, and also to the two inputs of a subtracting junction 192 in which the signal from the amplifier 116 is subtracted from the signal appearing at the output of amplifier 120.
  • the sum signal appearing at the output terminal 194 of the summing junction, and the difference signal appearing at the output 196 of the subtracting junction, are rectified by respective rectifiers 198 and 200 (which are preferably full-wave rectifiers) which may be provided with time constant circuits 202 and 204, respectively.
  • the outputs of rectifiers 198 and 200 are applied to the positive and negative terminals, respectively, of subtracting junction 206 which produces a difference signal at its output terminal 208 which is available to perform a logic function.
  • the front-back logic circuit and its function thus far described is similar to that in co-pending application Ser. No. 124,135 with one importantexception.
  • the voltage input control of the front-back logic was provided with logarithmic amplifiers which, because of the limitations of practical amplifiers of this type limited the sensitivity and range of control that could be exercised with signals of widely varying levels.
  • the use of automatic gain control amplifiers 116 and 120 to keep the signal level at a high, substantially constant value greatly enhances the action of the front-back logic.
  • the present embodiment of the front-back logic also differs from the previously described embodiment in b.
  • the second column gives the relative signal voltage at the L terminal and its phase position.
  • the third column gives the relative signal voltage at the R terminal and its phase position.
  • the fourth column gives the absolute value of the junction 206 is applied to a parallel back-to-back juncphasor Sum of the left and right signals L and R tion of rectifiers 210 and 212, and the output of this junction after suitable amplification by an amplifier ee fifth column gives the absolute value of the 214, applied to the other terminal of summing junction PhaSor difference r and 1- (ahsolute values are 176.
  • the rectifiers 210 and 212 are appropriately bi- Used in the Computation Since the phasors are rectiaged (not shown) o f ti as a li to permit fled prior to subtraction, this being tantamount to only front-back control signals exceeding a predeter- Obtalhlhg an absolute Valuemined am litude to be a li d t h j i 176, Th f.
  • the first column is the bearing angle of panning in degrees, with 0 corresponding to center front; 45 to right front; to right back; and to center back, etc.
  • the voltage generated at the output terminal 174 of the wave-matching logic has been calculated and the results plotted in FIG. 4.
  • the solid line circle 230 represents unity voltage, and it is seen that there are four symmetrical lobes 232, 234, 236 and 238 each having a maxima of unity and centered at 45, 135, 225 and 315,
  • the sum of the signal produced by the wave-matching logic (the action of which on the gain control amplifiers 74-80 has been described previously) has added to it in junction 176 the signals from the front-back logic represented by lobes 220 and 222 The resulting sum signal is applied through transmission elements 178 and- /or 180 to the control electrodes of the gain control amplifier to achieve enchanced separation between front and back signals.
  • the phasors appearing in the squares labeled R and L,, and L; correspond to phasor groups 94, 92 and 90, respectively.
  • the desired signals at the front loudspeakers are equal and in phase, while the undesired side-effect signals are equal and out-of-phase. If the latter two signals are attenuated, then only the desired front signals remain.
  • the 45 position which corresponds to input to the right front channel, it is noticed that the side-effect signals are equal and at 90 to each other.
  • the desired signals are of equal amplitude (0.866) and are within of each other, while the side-effect signals in both cases are equal and out-of-phase.
  • the unwanted signals are equal and either in quadrature or out-of-phase relationship.
  • Amplitudes the phasors of the signals from TABLE 11 are depicted in FIG. 5 for eight positions of the panning control, spaced 45 apart.
  • the direction of the arrows in the central square refer to the panning position (that is, the arrow labeled 0 represents a center front signal, which would be applied equally to the left front and right front channels, and the 180 position would represent a center back signal which would be applied equally to the left back and right back channels), and 1 the arrows appearing in each of the eight surrounding adjacent channels and to control the gain of the output amplifiers for such channels to be attenuated whenever these voltages are in quadrature or in an out-of-phase condition, side-effect signals will be completely eliminated, while at the same time the wanted signals are properly emphasized. This is precisely the action of the combined wave-matching logic and the front-back logic described above. I
  • phasors 90-96 are reproduced, in solid lines, and enlarged to show more detail, and the dash-line phasors are the ones resulting from cross-blending portions of the phasors from L,” into R,”, and vice versa, and from cross-blending portions of the phasors from L,” into R,,”, and vice versa.
  • the amount of cross-blend illustrated in FIG. 6 is 50 percent, primarily for clarity of illustration, the usual amount of blending being in the vicinity of and percent for m and n.
  • the crossblending causes a center front signal to be increased to a value of 1.06C, in the two front channels, and a center back signal in the two front channels to be greatly diminished, namely, to 0.353C;,'.
  • a center back signal is increased to l.O6C, in the back channels, and a center front signal C, is reduced in the back channels to 0.353C,.
  • the initial favorable positioning of the front and back phasors resulting from intermixing simplifies the task to be performed by logic circuitry and thus serves an important purpose whether used simply as a feature of the matrix decoder, or as a feature of a matrix decoder combined with more sophisticated, and consequently more expensive, logic and control circuitry.
  • the matrix of FIG. 2A is a linear additive device, and the cross-blending operation but another additive operation, the circuitry of the matrix may be simplified somewhat without degrading the above-described operation.
  • the input to gain control amplifier 76 is composed of and the input to amplifier 78 is junctions 70 and 72 can be designed to perform the required operations thereby to eliminate the need for junctions 102 and 104.
  • matrix decoding means including first and second input circuits to which said first and second composite signals are respectively applied, said input circuits including means for shifting the phase of one of said composite signals relativet'o the otherby subs tantially f5r positioning said common signals in one of said relatively phase-shifted composite signals either in phase coincidence of in phase opposition with corresponding ones of said common signals in the other of said relatively phase-shifted composite signals,
  • Apparatus according to claim 1 wherein at least some of the said fractions have a value in the range of 0.25 and 0.35.
  • matrix decoding means including first and second input circuits to which said L, and R, composite signals are respectively applied, said first and second input circuits respectively including first and second pairs of all-pass phaseshifting networks to both of which the corresponding input signals is applied, a first phaseshifting network of each pair being operative to shift the phase of the applied signal by a predetermined reference angle and the second phaseshifting network of each pair being operative to shift the phase of the applied signal by an angle differing from said reference angle by substantially 90, first, second, third and fourth output channels adapted to be coupled to the loudspeakers positioned at the left front, right front, left back and right back corners, respectively, of said listening area, means for coupling the composite signals from the first network of said first and second pairs, respectively containing said L, and R; components as predominant components, to said first and second output channels, respectively, first means for combining substantially equal proportions of the composite signals from the second network of said first pair and from the first network of said second pair and for coupling to said third channel a composite signal containing said L component as
  • said first, second, third and fourth output channels respectively include first, second, third and fourth gain control amplifiers connected for respectively coupling said first,
  • control circuit for controlling the gains of said gain control amplifiers to enhance the realism of the four channel sound reproduced by the loudspeakers, said control circuit comprising:
  • control signal generating means connected to receive composite signals from the second network of said first pair and from the first network of said second pair and operative to derive therefrom first, second, third and fourth auxiliary composite signals of substantially constant amplitude regardless of the amplitudes of said composite signals and respectively containing the information contained in the composite signals in said first, second, third and fourth channels, first circuit means for comparing said first and second auxiliary composite signals and operative to produce a first signal indicative of whether they contain substantially equal amplitude signals in phase coincidence or in phase opposition,
  • Apparatus in accordance with claim 9, further including means for comparing the sum and the difference of said first auxiliary signal and the composite signal from the first network of said first pair and operative to produce a second control signal of a given polarity or opposite polarity depending on whether the sum exceeds the difference, or vice versa, and means for combining said second control signal with the control signal from said control signal generating means for application to said gain control amplifiers to enhance the separation between signals contained in said first or said second channels, or in both of said first and second channels, relative to signals contained in said third and said fourth channels, or in both of said third and fourth channels.
  • control signal generating means includes first and second auxiliary gain control amplifiers each having input and output terminals and a control electrode,
  • first and second auxiliary gain control amplifiers are operative to produce first and second auxiliary composite signals, respectively, at their respective output terminals corresponding to the composite signals applied thereto,
  • Apparatus further including a third auxiliary gain control amplifier for coupling the composite signal from the first network of said first pair to said means for comparing the sum and difference of it and said first auxiliary signal, said third auxiliary gain control amplifier having input and output terminals and a control electrode, and means coupling the composite signal from the first network of said first pair to the input terminal of said third auxiliary gain control amplifier, and wherein said last-mentioned circuit means is connected to the control electrode of said third auxiliary gain control amplifier and operative to maintain substantially constant the amplitude of the amplified composite signal appearing at the output terminal of said third auxiliary gain control amplifier regardless of changes in amplitude of said L signal.
  • first and second signal subtracting junctions to which said rectified first and second and said rectified third and fourth signals are respectively applied and which are respectively operative to produce said first and second signals respectively proportional to the difference between said first and second rectified signals and between said third and fourth rectified signals.
  • Apparatus according to claim 13 wherein said means for comparing the sum and difference of said first auxiliary signal and the composite signal from the first network of said first pair comprises a summing junction and a subtracting junction, each having first and second input terminals and an output terminal,
  • first. second, third and fourth output channels respectively include first, second, third and fourth gain control amplifiers for respectively coupling said first, second, third and fourth composite output signals for a respective loudspeaker, and further including a control circuit for producing a control signal for selectively controlling the gains of said gain control amplifiers to enhance the front-to-back channel separation, said control circuit comprising:
  • said sum and difference comparing means comprises a summing junction and a subtracting junction, each having first and second terminals and an output terminal,
  • JEEBH'iHZETr'EuTFEESHs including "first and second pairs of all-pass phase-shifting networks connected to receive said first and second composite signals, respectively, a first phase shifting network of each pair being operative to shift the phase of the applied signal by a predetermined reference angle and a second phase-shifting network of each pair being operative to shift the phase of the applied signal by an angle differing from said reference angle by substantially 90, and means for selectively combining predetermined portions of said relatively phase-shifted first and second composite signals to produce third and fourth composite signals respectively containing said L,, and said R component signals as its predominant component, signal-coupling means connected to receive and operative to couple composite signals respectively containing said L], R,, L, and R component signals as its predominant signal to respective ones of said sound-reproducing devices said signal-coupling means including signal amplitude-modifying means for separately adjusting the amplitude 6f the coniposite signal applied thereto, and control circuit for producing and applying to said signal amplitude-modifying means a control signal to enhance the
  • Apparatus in accordance with claim 18, further comprising means for summing and differencing the signals of said first set of control-signal-producing signals to produce sum and difference signals, and means for comparing the absolute magnitudes of said sum and difference signals to produce and apply to said signal amplitude-modifying means a second control signal of a given polarity or opposite polarity depending upon whether the sum exceeds the difference, or vice versa.
  • control signal generating means includes first and second auxiliary gain control amplifiers each having input and output terminals and a control electrode and connected to receive at their respective input terminals the signals of said second set of control-signal-producing signals, said first and second auxiliary gain control amplifiers being operative to produce first and second auxiliary composite signals at their respective output terminals corresponding to the composite signals applied thereto, means connected to the output terminals of said first and second auxiliary gain control amplifiers for selectively combining the auxiliary composite signals appearing thereat and operative to produce third and fourth auxiliary composite signals containing the information contained in the composite signals in said third and fourth channels, respectively, and circuit means connected to the control electrodes of said auxiliary gain control amplifiers and operative in response to at least one of said first, second, third and fourth auxiliary composite signals to maintain substantially constant the amplitude of said first, second, third and fourth auxiliary signals regardless of changes in the amplitude of said first and second composite signals.
  • Apparatus according to claim 21, including a third auxiliary gain control amplifier to the input terminal of which one of the control signal-producing signals to said first set is applied, and wherein said lastmentioned circuit means is operative to maintain substantially constant the amplitude of the output composite signal from said third auxiliary gain control amplifier regardless of changes in amplitude of said first and second composite signals.
  • said means for comparing the absolute magnitudes of said sum and difference signals comprises a summing junction and a subtracting junction, each having first and second input terminals and an output terminal, means connecting the composite output signals from said first and third auxiliary gain-control amplifiers to the first and second input terminals, respectively, of both said summing junction and said subtracting junction, means for separately rectifying the signals appearing at the output terminals of said summing and subtracting junctions, I
  • decoding circuit means connected to receive said first and second composite signals and operative in response thereto to produce third and fourth com posite signals respectively containing predominant Lb and Rbcomponent signals and each including sub-dominant L; and R, component signals, said decoding circuit means including first and second pairs of all-pass phase-shifting networks to which said first and second composite signals are respectively applied, a first phase-shifting network of each pair being operative to shift the phase of the applied signal by a predetermined reference angle and the second phase-shifting angle of each pair being operative to shift the phase of the applied signal by an angle differing from said reference angle by substantially 90,
  • signal amplitude-modifying means connected to receive and operative to couple said first, second, third and fourth composite signals to respective ones of said sound-reproducing means
  • control signal generating means for producing a control signal for selectively controling the transmission characteristic of said signal amplitudemodifying means to enhance the separation between frnt and back channel signals, said control circuit including:

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US00155976A 1971-06-23 1971-06-23 Apparatus for reproducing quadraphonic sound Expired - Lifetime US3798373A (en)

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JP (1) JPS5110963B1 (fr)
AU (1) AU464001B2 (fr)
BE (1) BE785279A (fr)
CA (1) CA973806A (fr)
DE (1) DE2230842C3 (fr)
FR (1) FR2143325B1 (fr)
GB (1) GB1396352A (fr)
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3885099A (en) * 1972-12-01 1975-05-20 Sony Corp Integrated logic circuit for the decoder of a multi-channel stereo apparatus
US3911220A (en) * 1971-08-06 1975-10-07 Sony Corp Multisound reproducing apparatus
US3937885A (en) * 1974-09-06 1976-02-10 Motorola, Inc. Control circuit for a matrixed four channel audio reproducing system
US3943286A (en) * 1973-03-29 1976-03-09 Sony Corporation Variable gain control circuit
US3944735A (en) * 1974-03-25 1976-03-16 John C. Bogue Directional enhancement system for quadraphonic decoders
US4799260A (en) * 1985-03-07 1989-01-17 Dolby Laboratories Licensing Corporation Variable matrix decoder
US4862502A (en) * 1988-01-06 1989-08-29 Lexicon, Inc. Sound reproduction
US5046098A (en) * 1985-03-07 1991-09-03 Dolby Laboratories Licensing Corporation Variable matrix decoder with three output channels
US5136650A (en) * 1991-01-09 1992-08-04 Lexicon, Inc. Sound reproduction
US5796844A (en) * 1996-07-19 1998-08-18 Lexicon Multichannel active matrix sound reproduction with maximum lateral separation
US5870480A (en) * 1996-07-19 1999-02-09 Lexicon Multichannel active matrix encoder and decoder with maximum lateral separation

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2252132C3 (de) 1972-10-24 1982-08-26 Sansui Electric Co., Ltd., Tokyo Decodierer für ein 4-2-4-Matrixsystem
JPS5453831U (fr) * 1977-09-22 1979-04-13
JPS54137248U (fr) * 1978-03-17 1979-09-22

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3632886A (en) * 1969-12-29 1972-01-04 Peter Scheiber Quadrasonic sound system
US3646574A (en) * 1970-05-25 1972-02-29 Howard S Holzer Compatible stereo generator
US3684835A (en) * 1970-07-29 1972-08-15 Parasound Inc Four channel stereo synthesizer

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3632886A (en) * 1969-12-29 1972-01-04 Peter Scheiber Quadrasonic sound system
US3646574A (en) * 1970-05-25 1972-02-29 Howard S Holzer Compatible stereo generator
US3684835A (en) * 1970-07-29 1972-08-15 Parasound Inc Four channel stereo synthesizer

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Four Channels and Compatibility, by Scheiber. Audio Engineering Society Preprint, Oct. 12 15 1970. *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3911220A (en) * 1971-08-06 1975-10-07 Sony Corp Multisound reproducing apparatus
US3885099A (en) * 1972-12-01 1975-05-20 Sony Corp Integrated logic circuit for the decoder of a multi-channel stereo apparatus
US3943286A (en) * 1973-03-29 1976-03-09 Sony Corporation Variable gain control circuit
US3944735A (en) * 1974-03-25 1976-03-16 John C. Bogue Directional enhancement system for quadraphonic decoders
US3937885A (en) * 1974-09-06 1976-02-10 Motorola, Inc. Control circuit for a matrixed four channel audio reproducing system
US4799260A (en) * 1985-03-07 1989-01-17 Dolby Laboratories Licensing Corporation Variable matrix decoder
US5046098A (en) * 1985-03-07 1991-09-03 Dolby Laboratories Licensing Corporation Variable matrix decoder with three output channels
US4862502A (en) * 1988-01-06 1989-08-29 Lexicon, Inc. Sound reproduction
US5136650A (en) * 1991-01-09 1992-08-04 Lexicon, Inc. Sound reproduction
US5796844A (en) * 1996-07-19 1998-08-18 Lexicon Multichannel active matrix sound reproduction with maximum lateral separation
US5870480A (en) * 1996-07-19 1999-02-09 Lexicon Multichannel active matrix encoder and decoder with maximum lateral separation

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DE2230842B2 (fr) 1980-02-21
FR2143325A1 (fr) 1973-02-02
JPS5110963B1 (fr) 1976-04-08
DE2230842A1 (de) 1972-12-28
AU4377572A (en) 1974-01-03
DE2230842C3 (de) 1980-10-16
AU464001B2 (en) 1975-08-14
BE785279A (fr) 1972-10-16
NL7208607A (fr) 1972-12-28
GB1396352A (en) 1975-06-04
CA973806A (en) 1975-09-02
FR2143325B1 (fr) 1979-04-06
IT958512B (it) 1973-10-30

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