DE2330577C2 - Four-channel stereo decoder - Google Patents

Description

Speaker should be released, then the simultaneous release of the other crosstalk signal component is prevented if a solo voice or a solo instrument is in a middle front position. Moreover, the four-channel stereo decoder according to the invention can be shown in FIG can advantageously be implemented relatively easily as an integrated circuit arrangement, whereby results in a simple and inexpensive circuit structure for construction and for maintenance.

The mixer circuit preferably contains two field effect transistors which, with their source-drain paths, each have the outputs of two adjustable ones Connect amplification circuit c. This has the advantage of a particularly low level of circuitry Effort for the mixed circuit with itself.

The control circuit expediently has between the outputs of the two subtraction circuits and subsequent rectification circuits on integrators. This brings the advantage of a special simple yet effective control circuit with themselves.

The control circuit expediently has integrators. between the outputs of the Matrix circuit downstream full-wave rectifiers and a differential circuit downstream of these full-wave rectifiers are provided. this has the advantage of a particularly simple and particularly effective control circuit.

The invention is explained in more detail below with reference to drawings, for example Drawings shows

F i g. Figure 1 is a schematic diagram of coding and decoding circuitry of the type used in the present invention Invention to be used:

F i g. FIG. 2 is a schematic circuit diagram of a decoding device with logic circuit arrangements according to FIG an embodiment of the invention;

F i g. 3 and 4 waveforms of output signals that were generated on the Upper passage 86 are derived to explain the Operation of the circuit shown in FIG. 2 is shown; F i g. 5 a schematic representation of the sound sources an original sound field described in the following description;

F i g. 6 a schematic representation of the output « signals a «» rectifier at the »n F i g. 2 illustrated embodiment for differently arranged Sound signals;

7 shows a signal curve to explain the Generation of a certain signal at transition 86 like this in the embodiment according to FIG. 2;

F i g. 8 shows the phase components of a center-back signal for explaining the present invention;

f 1 g. 9 is a schematic representation of the output signal of a track judge in the embodiment SS according to FIG. 2 for differently arranged audio signal sources and

F i g. 10 and 11 vector images of the output signals from a summing transition or a subtraction transition.

1 shows a quadrophone sound system in which the present invention is to be used. An encoder 18 receives left-front, left-back, right-back, and right-front signals (Lf), (Lg) and (R ₈ ) or (Rf) at its input terminals 10 «or 12 or 14 bzr /. 16. It also receives a center-front signal (Cf) at half the amplitude at its input terminals 10 bkw. 16 and also with half Amplitude a middle-Hmten signal (Cb) at its Input terminals 12 or 14. The encoder converts convert these input signals into two output signal mixtures with i-rbzw. Are labeled and those on his Output terminals 20 and 22 occur. The phase components of these signals are indicated by the vector images next to the corresponding terminals represented These mixed signals can be identified in a complex representation as follows:

Lt = L _f - 0.707 A ₈ + J (0.707 L ₈ ) Rr = Rf + 0.707 La - j (0.707 R _B ) (if Cp and C _{8 are} not available)

Decoded composite signals can then be fed to any two-channel medium, such as represented by the channels 23 and 25, which can be, for example, the two sound channels of a stereo record, a two-channel magnetic dance or an FM multiplex broadcast system.

After the recovery from the two-channel medium, the composite signals r and Ri are applied to two input terminals 30 and 32, respectively, of an encoder 34. The composite signals are then phase-shifted with pairs of phase shifters 38 or 40 and 42 or 44 such that the selective addition and subtraction gives four output signals, each of which contains a predominant component which corresponds to one of the original input signals. The basic phase shift angle Ψ introduced by the phase shifter is a function of frequency.

The network 38 thus shifts the composite signal Lt by the basic phase shift angle Φ. while the Φ network shifts the composite signal Lt by a phase angle of Ψ + 90 ° and the network 42 shifts the signal mixture Rr by a phase angle of 9 + 90 ° and the network 44 shifts the composite signal Rt by the basic phase shift angle Ψ. .n an output terminal 62 and the output signal of the phase shifter 44 is applied to an output terminal 68. The same negative components of the output signals of the phase shifters 40 and 44, i.e. -0707 of the output signals of the phase shifters 40 and 44 are combined in a summing junction 46, the signal obtained being applied to the output terminal fA of the decoder 34. The first, the second, the third and the fourth output signal, which appears at the output terminal 62, 64, f * or 68 of the decoder 34, contains mainly the Orial Lu Le or found Rrund various (-3 dB) components of a Size of 0J07 of the other signals, as represented by the vector groups 54, 56 and 58 aod 60. These vector groups are marked with LJ. L * izw. R ₉ ' and RJ

On the basis of the rig.2 wad the audible reproduction these signals through a circuit that is specially designed for this purpose described. The ones at the output terminals 62, 68, 64 and 66 appearing signals are fed to the inputs of the controllable amplifiers 70, 76 and 72 and 74, respectively The output signals of these amplifiers 70, 76 and 72 and 74 are applied to full wave rectifier circuits 70, 80 and 82 and 84, respectively Full wave rectifier circuits consists in the

to eliminate negative voltages, so that a signal with a phase difference of 180 ° is the equivalent of a Phase difference of 0 ° for balanced signals.

The output signal of the full-wave rectifier 80 is subtracted from the output signal of the full-wave rectifier 70 in a subtracter 86. Its output signal is applied to a full wave rectifier 90 through a time constant circuit 95. The output of the full wave rectifiers is applied to a limiter circuit 96. The output of the limiter circuit 96 is applied to the positive input terminal of a differential amplifier 94. The output signal of the full-wave rectifier 84 is subtracted from the output signal of the full-wave rectifier 82 in a subtracter 88 . The output signal of the subtracter 88 is applied to a full wave rectifier 92 via a time constant circuit 96.

The output of the rectifier 92 is over

a Bczrm7Cr * "*" * ⁱ ·· '"*' ^(Λα ■ *** ^ ·""*> CTOlivA Ρίησαηστ-

terminal of amplifier 94 applied. The output signals of the full wave rectifiers 78, 80, 82 and 84 are combined in a summing stage 151 , the output signal being used to control the gains of the amplifiers 70, 76, 72 and 74 with variable gain. The amplifiers 70, 72, 74 and 76 for controlling the gain are selected with identical or very similar parameters. The elements 70 to 94 form a control circuit A, which is also called a wave adaptation circuit A here.

The elements described above generate a first control signal at the positive output terminal of the differential amplifier 94, this signal being applied to a summing stage 106 via a time constant circuit 104. A second control signal having a relation to the first control signal opposite polarity is applied to Jer negative output terminal generates the differential amplifier 94 and applied to a summing stage 116 for a second time constant circuit 114. The output of the summing stage 106 is via a limiter 108 to the gain <; teuerkleminen the amplifiers 100 or 102 with a variable gain. The inputs to amplifiers 100 and 102 are the signals appearing at outputs 62 and 68, respectively, of decoder 34.

The second control signal is applied from the summing stage 116 via a limiter 1 18 to the control terminals of the gain of the amplifiers 110 and 112. The inputs of the amplifiers 1 10 and 112 are 66 derived of the decoder 34 of d'_n output terminals 64 and the output signals of the Amplifiers 100, 102, 110 and 112 are fed to speakers 120 and 122 and 124 and 126, respectively. These speakers are placed in the left-front, right-front, left-back and right-back corners of a room

It is assumed that the crosstalk components of Ls and Rb are not included in the output signals Lf ' and Rf appearing at output terminals 62 and 68, respectively; a signal which is either positive (Lf exceeds Rf) or negative (R _F exceeds Lf) appears at the output of connection 86. Since the middle Vornsignalkomponen.ten of the signal (Cf) in the signals Lf and Rf with the same phase are present and have the same amplitude, they are deleted in the subtracter 86 , so that no center-front signal appears at the output of the adder 86.

The difference signal from subtracter 86 is a positive signal after rectification by full wave rectifier 90. Thus, if the sound signal is in the left-front position, as in FIG. 5 appears, a relatively large positive signal appears at the output of the rectifier 90 (FIG. 5). If only a center-front signal is predominant (position no. 2). so no signal appears at the output of the rectifier 90. If a right-front tone signal (Rf) appears (the third position), a relatively large positive signal appears at the output of the rectifier 90. It can thus be said that if the original sound / between positions one and two (left front and middle front) is present, the control signal, which is applied to the positive terminal of the differential amplifier 94, changes on a line 130 , as shown in FIG. 6 is shown. When the original sound between the second and aer rlritipn position (center front and right front), so the control signal varies along a line 132nd

On the other hand, if the left-front and right-front signals (Lf and Rf) are not included in the signals Ly and Rf -> and only the crosstalk components Ls and Rb are included, only a small positive signal appears in the output stage of the rectifier 90. This small positive signal represents the differences in the components Lh in the signals Lf W and Rf , which have a phase difference of 90 ° from one another. The combined signal Rb. as shown in Fig. 7, ha! a generally triangular waveform. A similar signal is generated by subtracting the 90 ° phase difference from non-predominant Ji seeing /? E signal components. As shown in FIGS. 5 and 6, a small positive signal appears at the output of the rectifier 90 if only the right-rear signal in position 4 is generated. When the tone appears in the center-back position or fifth position, no output signal appears on the rectifier 90, and when the signal appears in the left-rear position or the sixth position, a small positive signal appears again appears at the output of the rectifier 90. ⁴ > It can thus be said that the phase component Cb is composed into a whole by the non-predominant components of R ₈ and L ₈ in the signals Lf and Rf ' . However, these two signals Ce composed into a whole are of the same amplitude and out of phase with one another (as shown in FIG. 8), so that they are deleted in the subtracter 86.

If the original signal is between positions three and four (right front and right rear), position four and five (right rear and middle rear) or position five and six (middle rear and left rear), this varies in the output stage of the rectifier 90 appearing control signal corresponding to a curve as illustrated by the lines 134, 136 or 138, as Figure 6 shows Therefore, the two center-fore-and middle-rear signal components in the signals Lf and Rf ' are deleted in the subtracter 86, which feature is important in the operation of the control circuit or logic circuit A. A similar result is achieved for the signals Ld and R _B '
The amplitude characteristic of the output signal,

which appears at the output of rectifier 92 is shown in FIG. 9 shown. The crosstalk components of the center-front and center-back signals (Cr and Cb) included in the signals Lb and Rb are canceled in the subtracter 88 in a manner similar to that described above. Thus, if the signals are only predominant in the left-front or right-front positions, only a relatively small proportion of positive control signals is generated at the output of the rectifier 92.

By properly selecting the time constants in the time constant circuits 104 and 114 , it is possible to reduce this small voltage that exists when only the crosstalk components are in the signals Lf- '. Rr, Lb and Rb are included, this small voltage being reduced to zero. Since the output signals of the rectifiers 90 and 92 are applied to the limiter circuits 96 and 98, respectively, the limiting levels can also be selected (as indicated by the I_jn; p 140 in FI g. 6 g ??? 'g'). that the non-predominant or sub-dominant signals are canceled. Thus, the input signal applied to the positive input of amplifier 95 represents the difference between the main component Lr in the composite signal Lf and the main component Rr in the signal Rr , ie:

Similarly, an input signal applied to the negative input terminal of the amplifier 94, by appropriately selecting the limiting field of the limiting circuit 98, the difference between the main component Lb in the signal L '' and the main component Rb in the signal,? /) 'represent, or:

\\ Lb \ - \ Rb \\

With these two input signals, the output signals can be sent to the positive and negative Terminals of amplifier 94 are designated:

\\ Lf \ - \ Rf \\ - \\ Lb \ - \ Rb \\

These signals are applied to the control inputs of amplifiers 100, 102, 110 and 112 as described above. The two signals have opposite polarities, which are determined as follows. If the absolute value of the difference between L ^ and Rr is greater than the absolute value of the difference between L ₈ and Reist, if namely

so the polarity of the signal at the positive output terminal of amplifier 94 is such that the gains of amplifiers 100 and 102 are increased while the polarity of the signal at the negative output terminal of amplifier 94 is held at the opposite polarity to increase the gains of amplifier 110 and 112 to decrease accordingly. Signals which would otherwise be reproduced through speakers 124 and 126 are consequently not heard by the listener, and crosstalk signal components Lf and R ^ contained in signal Lb and Rb are substantially eliminated. Similar results are achieved in the other channels, that is, if the absolute value of the difference between the signal components L _B and R _{8 is} greater than the absolute value of the difference between Lf and R _F 'ßU, ie if

then an output signal with such a polarity arises at the negative output terminal of the amplifier 94 that the gain factors of the amplifiers 110 and 112 are increased, the control signal at the positive output terminal of the amplifier 94 being of the opposite polarity to the gain factors of the amplifiers 100 and 102 to belittle. This substantially eliminates the cross-talk component signals of Lb and Rb in signals Lr and Rr.

To underline the important features of the waveform matching circuit or control circuit A described above, it should be noted that since the components Lr and Rr are in phase in the signals Lr and Rr, respectively, the center-front signal Cr contained therein is canceled in the subtracter 86, similarly due to the fact that the center-back signals Cb contained in the signals Lr and Rr are out of phase, they are also canceled in the subtracter 86 (since a phase difference of 180 "as a phase difference is zero Similarly, the signal components Ln and Rb or the signals Lb and Rb are in phase, so that the center-back signal Cb contained therein is canceled in the subtracter 88 , as are the center-front signals Cr. Which are out of phase with each other and included in. This makes it unnecessary to have time constant circuits between the respective rectifiers 78 and 90 and the junction 86 and between n the respective rectifiers 82 and 84 and the transition 88 to be provided.

As explained above, the control circuit or the waveform matching circuit A does not generate an output control signal for the center-front or center-back signals. Since the center-front signal is particularly popular for the representation of solo voices or instruments, it is necessary to provide an additional, logic circuit arrangement or control circuit B , which recognizes these positions. The output signals of the amplifiers 70 and 76, which represent the signals Lr and Rr, respectively, are fed to the inputs of a summing element 150 and a subtracting element 152 in order to generate a sum signal 154 and a difference signal 156, respectively, as in FIG. 10 and 11 respectively. The sum signal 154 is fully rectified by a rectifier 158 and integrated by a parallel KC circuit 162 before it is applied to the positive input terminal of a differential amplifier 160 . The differential output signal from the subtraction element 152 is fully rectified by a rectifier I4 and integrated by a parallel RC circuit 166 before it is applied to the negative input terminal of the differential amplifier 160 . The circuits 162 and 166 act as time constant circuits. The elements 150, 152, 158, 164, 162, 166 and 160 form the logic circuit or the control circuit B for the front / rear separation.

The output signal from the positive terminal of the amplifier 160 forms a third control signal which is added to the first control signal in the summing element 106 . It is also applied to the gate electrode of a field effect transistor 170 , the drain and source electrodes of which are connected between the outputs of amplifiers 110 and 112 , respectively. The field effect transistor 170 acts as a mixer for mixing the output signals of the amplifiers 110 and 112 in FIG

Dependence on the third control signal. That derived from the negative output terminal of amplifier 160 The output signal forms a fourth control signal, which is linked to the second control signal in the Summing member 116 is added and also to the gate electrode of a field effect transistor 171? is applied, the drain and source electrodes between the Outputs of the amplifiers 100 and 102 are connected so that their output signals are dependent on the fourth control signal can be mixed.

It should be noted here that in the sum signal 154 (FIG. 10) the signal components /.f- and /? Hn are phase, but the signals /? _s and Lr are out of phase. Therefore, a center-back signal Cr (if any) is canceled in summer 150, but a center-front signal (if any) is still obtained. On the other hand, in the difference signal 156 (FIG. 11), the signal components L _F and Rf are out of phase, but the signal components L _B and R _{B are} in phase so that when the Milte-Vorn signal is present it is in the subtracter 152 cleared and the center-back signal Ce. if any, is obtained.

Thus, if a center-front signal is present, a signal will have a polarity which corresponds to the gain factors the amplifier 100 and 102 increases, appears on the positive output terminal 160, if

\ L _F '+ R _F ^l \ - \ L _F ' -R _F '\> 0

this third control signal is used to control the gains of amplifiers 100 and 102 to increase their gains and decrease the volume of the tones generated in left-front and right-from speakers 120 and 122, respectively. The third control signal is also applied to the gate electrode of the field effect transistor 172 so that the center-front signals contained in the signals La and R _B 'are mixed and canceled. A signal of the opposite polarity is generated at the negative output terminal of the amplifier 160, which reduces the gain factors of amplifiers 110 and 112 and reduces the FeWeffekt-

makes transistor 172 essentially non-conductive.

If other -> already the center-back signal is present. a signal of a polarity which increases the gain of amplifiers 110 and 112 appears at the negative output terminal of amplifier 160, this fourth control signal causing the gain of amplifiers UO and 112 to be increased and the output signals of amplifiers 110 and 112 to be mixed so that the center-back signals contained in signals L _F ' and Ry are canceled. A signal of the opposite polarity is formed at the positive output terminal of amplifier 160, which reduces the gain factors of amplifiers 100 and 102 and makes field effect transistor 170 essentially non-conductive.

Thus, the circuit elements of the decoder 34 according to the present invention can be formed on only one semiconducting carrier material. The circuit elements of the waveform matching circuit A and the front-rear logic circuit B can also be formed on only one semiconducting substrate without external time constant circuits. This greatly facilitates the manufacture of the decoding audio signal system in the form of an integrated circuit.

The mixing field effect transistors 170 and 172 connected to the front-rear logic circuit or control circuit B eliminate the mid-signals in the (back or front) channels to which they do not legitimately belong, at the same time the amplifier gains in the correct (front or rear) channels are increased and the amplifier gains in the wrong (rear or front) channels are decreased. In contrast to certain front-to-back logic circuits, the signal mixing of the present invention allows the gain factors of the amplifiers in the wrong channels to be reduced so that they are smaller than those in the prior art circuits so that the prevailing signals are not too can be reduced to a barely audible level.

For this purpose 3 sheets of drawings

Claims (4)

Patent claims: 1. Four-channel stereo decoder for converting two mixed signals (L _T , Rt), each of which contains a first or second predominant signal component (Lf or Rf) and two weaker signal components phase-shifted by 90 ", one of which (L ₀ ) contains one Composite signal (Lt) leads the other (R _a ), but lags behind in the other composite signal (Rt) , with a decoding matrix (34) which, in response to the two mixed signals (Lt, Rt) fed to it, emits four playback signals at four separate outputs, in each of which one of the four signal components (Lf, Rf, Lb, Rb) predominates, with adjustable amplifier circuits (100, 102, is 110,112), which is connected on the input side to the outputs of the Decoding matrix (34) are connected and amplifies the mentioned signal components on the output side submit, and with a control circuit (A, B) which is connected on the input side to the outputs of the decoder circuit (34) and which is connected with a diflerential amplifier circuit (94) on the output side to the control inputs of the adjustable amplifier circuits (100, 102, 110, 112) is characterized. that with the differential amplifier circuit (94) of the control circuit ( A, B) a first subtracting circuit (86). which receives the two above-mentioned predominant signal components (Lf, Rr) fed in fully rectified, and a second subtraction circuit (88) is connected. which the mentioned weaker Signalar parts (L "Rb) is fed fully rectified that the control circuit (A. B) .ne has a matrix circuit (ISO, 152) which receives the two above-mentioned predominant signal components (Lh. Rr) on the input side and which emits sum or difference signals of the relevant signal components on the output side. and that the adjustable gain circuits (100, 102, 110, 112) have associated therewith a mixer circuit (170, 172). which is controlled in this way by the said difference / signal. that undesired crosstalk signals at the outputs of the adjustable amplification circuits (100, 102, 110, 112) are eliminated. 2. Vlerkanal stereo decoder according to claim 1, characterized in that the mixer circuit (170, 172) has two field effect transistors (170, 172): o contains that with their source-drain routes respectively connect the outputs of two adjustable amplification circuits (100,102 or HO, 112). 3. Four-channel Stcreodecoder according to claim I or 2, characterized in that the control circuit (A. B ) has integrators (95, 97) between the outputs of the two subtraction circuits (86, 88) and subsequent rectification circuits (90, 92) 4. Four-channel stereo decoder according to one of claims 1 to 3, characterized in that the control circuit (A, B) has integrators (162, 166), the full-wave rectifiers (158, 164) connected downstream between the outputs of the matrix circuit (150, 152) ) and a differential circuit (160) following these full-wave rectifiers (158, 164) are provided. The invention relates to a four-channel stereo decoder for converting two signal mixtures, each of which contains a first or second predominant signal component and two ^{weaker signal components which are phase-shifted by 90 c} , one of which leads the other in one signal mixture but is disadvantageous in the other signal mixture.
with a decoding matrix which, in response to the two mixed signals fed to it, emits four playback signals at four separate outputs, in each of which one of the four signal components predominates,
with adjustable amplifier circuits that are connected on the input side to the outputs of the decoding matrix and on the output side emit the named signal components in amplified form, and
with a control circuit which is connected on the input side to the outputs of the decoding matrix and which is connected with a differential amplifier circuit on the output side to the control inputs of the adjustable amplifier circuits. A four-channel stereo decoder of the type described above is already known (publication »SO Logic Decoder-Theory of Operation "by Richard G. Allen and Benjamin B. Bauer, CBS Laboratories. 1st of May 1972). A disadvantage of this known four-channel stereo decoder, however, is that the output of Crosstalk signals. on loudspeakers is not avoided. There have also already been proposed circuit arrangements for processing or outputting quadraphonic signal mixtures (DE-OS 22 09 424. DE-PS 22 30 842. DE-PS 22 08 099. DE-OS 22 40 496). the basically to the previously explained known four-channel stereo decoder back D.imit also liable ^r the proposal in question. tin. Disadvantages. d \ " adhere to the well-known. four-channel stereo decoder The invention is accordingly based on the object of showing a way, as with a four-channel stereo decoder which is to be proceeded in the manner mentioned at the beginning. so that the emission of crosstalk signals from a loudspeaker is avoided in a particularly simple manner. where these signals are undesirable. The object indicated above is achieved with a four-channel stereo decoder of the type mentioned at the beginning Art according to the invention in that with the differential amplifier circuit of the control circuit a first subtraction circuit, which both i, named, predominant signal components fully rectified receives leads, and a second subtracting circuit is connected. which the mentioned weaker ones Signal components fed fully rectified receives that the control circuit has a matrix circuit which has the two above-mentioned predominant on the input side Receives signal components supplied and which sum or difference signals on the output side outputs the relevant signal components, and that the adjustable amplification circuits have a mixer circuit is associated. which is so controlled by said difference signal. that unwanted crosstalk signals at the outputs of the adjustable gain circuits are eliminated. The invention has the advantage that with a particularly low circuit complexity regarding the ineffectiveness of crosstalk signals can be managed. It is also advantageous that in the event that a Crosstalk signal component to the playback