MXPA00005869A - Post-amplification stereophonic to surround sound decoding circuit - Google Patents

Abstract

A post-amplification stereophonic to surround sound decoding circuit is described herein. The decoding circuit includes inputs to be connected to a stereophonic power amplifier to receive a powered amplified stereophonic signal and outputs to be connected to left and right main loudspeakers, to left and right secondary loudspeakers and to a central loudspeaker. The decoding circuit includes secondary channels decoding circuit decoding left and right surround channel signals to be supplied to the left and right secondary loudspeakers, respectively, and a central channel decoding circuit decoding a central channel signal to be supplied to the central loudspeaker. The central channel decoding circuit includes two decoupling capacitors decoupling the left and right signals from the powered amplified stereophonic signal before combining these signals to yield the central channel signal. This decoupling action prevents"bleeding"of the left and right signals that would degrade the stereophonic signal.

Description

STEREOPHONICAL POSTAMPLIFICATION FOR A CIRCUIT DECODIFYING SURROUNDING SOUND FIELD OF THE INVENTION The present invention relates to circuits that decode stereophonically surrounding sound. More specifically, the present invention relates to stereophonic post-amplification for a circuit that decodes surrounding sound to be installed between the outputs of a conventional stereophonic amplifier and a conventional loudspeaker. , BACKGROUND OF THE INVENTION Although monophonic sound is still widely used in modulated amplitude (AM) radio and telephone networks, stereo sounds are now considered the standard in high fidelity (HI-FI) applications. Stereo sound systems have as their main purpose to reproduce two channels of different sound, via speakers or speakers, in such a way that the sound reaches each ear of the listener giving the impression to the listener that it is taken to the place where the sound is recorded. Of course, the realism of this impression depends on many factors, such as, for example, the relative position of the listener with respect to the speakers and the quality of the record. The surrounding sound systems have been introduced into consumer electronic systems to create what is known as domestic theaters, where listening is subjected to different sounds coming from remote places in the room. The surround sound systems of the standard domestic theater are equipped with five speakers, each of which reproduces a I different sound channel. The circuits that decode the surround sound used in these surrounding sound systems can be broadly divided into two main types, namely, pre-amplification decoding circuits and post-amplification decoding circuits. The surround sound systems using the preamp decoders receive a stereo signal of two channels from a conventional low level and expand this to a surround sound of five channels. Each of these five channels is amplified separately and then supplied to a predetermined speaker. The five channels are generally determined as follows: a left main channel corresponds to the left channel of the stereo sound signal and is reproduced by a front left speaker; a main right channel corresponding to the right channel of the stereo sound signal and reproduced by the front right speaker; a secondary left channel (also called the left surround channel) is decoded by subtracting the main right channel from the main left channel and is played by the left rear speaker; a secondary right channel (also called the right surround channel) is decoded by subtracting the main left channel from the main right channel and is played by a right rear speaker; and a central channel is decoded by adding the left main channel and the main right channel, and is reproduced by a central speaker, usually mounted on top of the television screen. A major disadvantage of surround sound systems using preamp decoders is that a five-channel amplifier is necessary to reproduce the surrounding sound, since the power amplification is performed after decoding the surround sound of the stereophonic sound. The users of this technology can, therefore, acquire a dedicated power amplifier, which increases the total cost of the system. Post-amplification surround sound decoders usually solve the aforementioned advantage of the preamp decoders by providing an apparatus that can be installed between the amplified stereophonic signals outputs left and right of a conventional stereo amplifier and the five speakers or speakers mentioned above. . The stereo to decode surrounding sound is therefore effected, after the power amplification, which allows the use of a conventional stereophonic amplifier. U.S. Patent No. 5,265,166, issued November 23, 1993 to Madnic et al. , and titled: "MULTICHANNEL SOUND SIMULATION SYSTEM", describes such post-amplification stereophonic for the surrounding sound decoder. The system described by Madnick et al. it suffers major disadvantages that generally lead to a decrease in the quality of reproduction of the sound and to a greater complexity of the load imposed on the stereophonic amplifier. As will be readily understood by one skilled in the art, the return to ground of the negative terminal of the rear loudspeaker causes the power output to "see" an impedance different from the impedance of the conventional 8 ohm horn. In addition, the return to ground of the negative terminal of the center speaker via an inductance will also increase the complexity of the load of a power amplifier, which will inevitably lead to an increase in sound distortion and a total overall decrease in the reproduction of the sound. It should also be noted that the combination, via resistors, of the right and left channels to generate the central channel, will decrease the clarity of reproduction of the sound of the main right and left channels, since there are no provisions to prevent some "leakage" of the right channel in the left channel and vice versa. U.S. Patent No. 5,497,425, issued March 5, 1996 to Robert J. Rapoport and entitled: "SOUND SIMULATION DEVICE-MULTICHANNEL CIRCUNDER", describes a hybrid stereophonic for the surrounding sound decoder provided with features of the preamplification and post-amplification decoding described here above. The system proposed by Rapoport has many disadvantages. For example, a supplementary power amplifier must be provided to amplify the center channel before reproduction by the center speaker. In addition, the disadvantages discussed here above with respect to the Madnick et al. they apply in a general way to the Rapoport system, since the design philosophy is similar. GB 2,014,404 is also known, which discloses a 'stereophonic horn system for use in a car, where five speakers are connected to the two standard outputs of an amplifier. This system does not provide a surrounding sound decoding environment.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention, therefore, to provide an improved stereophonic post-amplification for an apparatus that decodes surrounding sound free of the aforementioned disadvantages of the prior art. More specifically, in accordance with the present invention, a stereophonic post-amplification is provided for a circuit that decodes surrounding sound comprising: an input for receiving a stereophonic signal amplified in power including a left channel signal and a right channel signal; a first output configured to be connected to a secondary left speaker; a second output configured to be connected to a secondary right speaker; a third output configured to be connected to a central speaker; decoding means of secondary channels for decoding a signal of the secondary left channel and a signal of the secondary right channel of the signals of the left and right channels of the stereophonic signal amplified in power; the secondary left channel signal is supplied to the first output and the secondary right channel signal is supplied to the second output; and decoding means of the central channel for decoding a signal from the center channel of the signals of the left and right channels of the stereophonic signal amplified in power; means for decoding the central channel including first and second decoupling means, respectively decoupling signals from the left and right channels; the decoding means of the center channel includes means for combining the signals of the left and right decoupled channels in the signal of the center channel; the signal of the central channel is supplied to the third output; whereby the decoupling means of the central channel decoding means allow the signals of the left and right channels of the amplified stereophonic signal to be combined without modification of the signals of the original left and right channels. According to another aspect of the present invention, a stereophonic post-amplification is provided for a circuit that decodes surrounding sound, comprising: an input for receiving a stereophonic signal amplified in power including a signal from the left channel and a signal from the right channel; a first 'output configured to be connected to a second secondary left speaker; a second output configured to be connected to a secondary right speaker; a third output configured to be connected to a center speaker; a fourth output configured to be connected to a main left speaker; a fifth output configured to be connected to a main right speaker; the decoding means of the secondary channels for decoding a signal of the secondary left channel and a signal of the secondary right channel of the signals of the left and right channels of the stereophonic signal amplified in power; the secondary left channel signal is supplied to the first output and the secondary right channel signal is supplied to the second output; the decoding means of the central channel for decoding a signal from the center channel of the signals of the left and right channels of the stereophonic signal amplified in power; the decoding means of the central channel includes first and second decoupling means for decoupling respectively the signals of the left and right channels; the decoding means of the center channel includes means for combining the signals of the left and right decoupled channels in the signal of the center channel; the signal of the central channel is supplied to the third output; and means for controlling the volume of the main channels to control the amplitude of (a) a signal from the left channel supplied to the fourth output of the left channel signal and (b) a signal from the right channel supplied to the fifth output of the channel. right channel signal; whereby the decoupling means of the decoding means of the center channel allow the signals of the left and right channels of the stereophonic signal amplified in power to be combined without modifying the signals of the original left and right channels. According to still another aspect of the present invention, there is provided a decoding circuit of the central channel for a stereophonic post-amplification for the device that decodes surrounding sound, characterized in that it comprises: an input for receiving a stereophonic signal amplified in power that includes a signal of the left channel and a signal of the right channel; an output configured to be connected to a center speaker; and decoding means of the central channel for decoding a signal from the center channel of the signals of the left and right channels of the stereophonic signal amplified in power; the decoding means of the central channel includes first and second decoupling means, respectively decoupling the signals from the left and right channels; the decoding means of the center channel includes means for combining the signals of the left and right decoupled channels in the signal of the center channel; the signal of the central channel is supplied to the output; whereby the decoupling means of the decoding means of the central channel allow the signals of the left and right channels of the stereophonic signals amplified in power to be combined without modifying the signals of the original left and right channels. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following non-restrictive description of a preferred embodiment thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Figure 1 illustrates a block diagram, a stereophonic post-amplification for the circuit decoding surrounding sound according to an embodiment of the present invention; the decoding circuit is connected to a stereophonic power amplifier and to five speakers; Figure 2 illustrates, in a schematic view, the stereophonic post-amplification for the circuit decoding the surrounding sound of Figure 1; and Figure 3 illustrates a schematic view, an alternative embodiment of the central channel decoding circuit illustrated in Figure 2.

DESCRIPTION OF THE PREFERRED MODALITY Turning now to Figures 1 and 2 of the accompanying drawings, a stereophonic post-amplification will be described for the circuit decoding surrounding sound 10. The decoding circuit 10 illustrated in FIG.

Figure 1 is shown connected to a stereophonic power amplifier 12. The decoder circuit 10 includes a left input 14, a right input 16 and a ground connection 18, respectively, connected to the left output 20, the right output 22 and a connection to ground 24 of the stereophonic power amplifier 12. Of course, connections 20, 22 and 24 of power amplifier 12 are usually connected to two conventional main left and main right speakers.

The decoder circuit 10 also includes two main left speaker outputs terminals 26, 27, connected to a main left speaker 28, and a two-terminal main right speaker output 30, 31 connected to a main right speaker 32, a speaker output left secondary of two terminals 34, 35 connected to the secondary left speaker 36, a secondary right speaker output of two terminals 38, 39, connected to a right secondary speaker 40 and a two-terminal central speaker output 42, 43 connected to a central loudspeaker 44. The decoder circuit 10 includes a volume control circuit of the main channels 46, a decoding circuit of the secondary channels 48 and a decoding circuit of the central channel 50. As can be seen from Figure 1, the circuit control of the volume of the main channels 46 interconnects the inputs 14, 16 and 18 and the outputs of the main speakers 26, 27, 3 0 and 31; the decoding circuit of the secondary channels 48 interconnects the inputs 14 and 16 and the outputs of the secondary speakers 34, 35, 38 and 39; and the decoding circuit of the central channel 50 interconnects the inputs 14, 16 and 18 and the outputs of the center speaker 42 and 43. Turning now to Figure 2 of the accompanying drawings, circuits 46, 48 and 50 will be described in more detail. The volume control circuit of the main channels 46 includes a variable resistor 52 connected to the left input 14 and the output 26 of the main left speaker and a variable resistor 54 connected to the right input 16 and to the output 30 to the right speaker principal. By varying the volume of the resistors 52 and 54, the amplitude of the signal supplied to the main loudspeakers is modified, thereby varying the volume of the sound reproduced by the main loudspeakers, since the portion of the signal amplified in power that It dissipates as heat in the resistance is modified. As can be seen from Figure 2, the ground connections 27 and 31 are interconnected and connected to the ground connection 18. It should be noted that the variable resistors 52 and 54 could be advantageously incorporated together in a stereo L-shaped adapter. (without ground connection) and have an appropriate power value. In this case, the user will only face a control of volume for the two main speakers. Alternatively, the variable resistors could also be incorporated by means of a plurality of discrete high quality resistors (not shown) and switches (not shown) or by an integrated circuit of variable resistance of high power levels (not shown). Thus, it should be noted that the term "variable resistance" was used, here in the appended claims, as an electronic element or arrangement of resistive and / or other electronic elements that allow the modification of a resistance between two points of an electrical circuit. The decoding circuits of the secondary channels 48 include a first capacitor 56 connected to the left input 14 and to the output 34 to the secondary left speaker, a second capacitor 58 connected to the right input 16 and to the output 38 to the secondary right speaker and a resistor variable 60 connected to the grounding connection 35 to the secondary left speaker and to the grounding connection 39 to the secondary right speaker. It should be noted that the grounding connections 35 and 39 are not connected to the ground connection 18.

As will be appreciated by those skilled in the art, the connection of the variable resistor 60 between the ground output connections 35 and 39 causes the secondary loudspeaker to reproduce the respective secondary channel signals that are obtained by an action of the signal supplied to the inputs 14 and 16. More specifically, the signal of the secondary left channel is reproduced by the secondary left speaker and the signal supplied to the left input 14 minus the signal supplied to the right input 16. Similarly, the signal of the secondary right channel is reproduced by the secondary right speaker and the signal supplied to the right input 16 minus the signal applied to the right input 14. Since the decoding circuit of the secondary channels 48 is not connected to ground, the signals of the secondary left and right channels are the same, since the subtraction from input 14 of input 16 is equal to subtraction of the input 16 of the input 14. Furthermore, since the capacitors 56 and 58 are, in a sense, decoupling capacitors, and since the decoding circuit of the secondary channels 48 is not connected to ground, the interconnection of the ground connections 35 and 39 will have no harmful effect on the signals supplied to the volume control circuit of the main channels 46 and to the decoding circuit of the center channel 50, since the capacitors 56 and 58 prevent the signal supplied to the input 14"leaks" in the signal supplied to input 16 and vice versa. By varying the value of the resistance 60, the amplitude of the signal provided to the secondary loudspeakers is amplified, thereby varying the volume of the "sound reproduced by the secondary loudspeakers, since the portion of the amplified signal in power is dissipated. As heat in the resistance, it is modified It has been found advantageous to select the value of the capacitors 56 and 58, so that a high pass filter of about 100 Hz is created with respect to the impedance of the secondary loudspeaker. decoding of the central channel 50 includes a first fixed-value resistor 62 connected to the left-hand input 14, a first capacitor 64 connected to the first resistor 62, and a second fixed-value resistor 66 connected to the right-hand input 16, a second capacitor 68 connected to the second resistor 66 and a variable resistor interconnecting both capacitors 64 and 68 to the output 42 of the center speaker. to ground 43 is connected to the ground input connection 18. The signal supplied to the output of the center speaker 42 is therefore the addition of the signal supplied to the left and right inputs 14 and 16 by the power amplifier. 12. It should be noted that, since capacitors 64 and 68 are, in a sense, decoupling capacitors, the interconnection of the output of those capacitors will cause the addition of the left and right inputs 14 and 16 to have no effect on the signals supplied to the volume control circuit of the main channels 46 and to the decoding circuit of the secondary channels 48. It has been found advantageous to select values of the fixed resistors 62 and 66, so that each is equivalent to half the impedance nominal of the main speakers. It has also been found advantageous to select values from capacitors 64 and 68 so that a high pass filter of approximately 100 Hz is created with respect to the impedance of the center speaker. Again, by varying the value of the resistor 70, the amplitude of the signal supplied to the center speaker is modified, thus varying the volume of the sound reproduced by the center speaker, since the portion of the amplified signal in power that is dissipates as heat in the resistance is modified. ^^ 8r It should be noted that variable resistances 60 5 and 70 could be advantageously incorporated into separate L-shaped monophonic adapters (without ground connections) and have appropriate power values. Alternatively, the variable resistors 60 and 70 could also be 'incorporated by a plurality of high quality, discrete resistors (not shown) and switches (not shown) or by variable resistance integrated circuits of high power levels (not shown). Turning now to the drawings in Figure 3, will briefly describe a central decoding circuit to the alternative channel 150. The main difference between the decoding circuit 150 and the decoding circuit 50 of Figure 2 consists in the replacement of the variable consistency 70 provided by the current below the interconnection of the left and right inputs by a pair of variable resistors 170, 170 'respectively, provided between the fixed-value resistors 62, 66 and the capacitors 64, 68, thus upstream of the interconnection of the tickets left and right. The registration circuit 150 incorporates the impedance and stability and also allows more useful power to be supplied to the center speaker. Again, it should be noted that the variable resistors 170 and 170 'could be advantageously incorporated together in an L-stereophonic adapter (without ground connection) and have an appropriate power value. Alternatively, variable value resistors could also be incorporated by a plurality of discrete high quality resistors (not shown) and switches (not shown) or by a high power level variable resistor integrated circuit (not shown). Returning to Figure 2, it should be noted that the stereophonic post-amplification impedance for the circuit decoding surrounding sound 10"observed" by the outputs 20, 22 and 24 of the power amplifier 12 is essentially similar to the impedance of the main speakers, since that the decoding circuits 48 and 50 use decoupling capacitors and are therefore virtually "invisible" in terms of impedance. In fact, the impedances of the decoding circuits 48 and 50 are so high that the impedance of the main loudspeakers 28 and 32 of the connection of the circuits 48 and 50, is generally parallel, between them without significantly modifying the impedance observed by the outputs 20, 22 and 24 of the amplifier < »J power. As can be seen from Figure 2, fuses 72, 74 and 76 are provided between the inputs, 14, 16 and 18 and the circuits 46, 48 and 50 as protection. It should also be noted that an on / off switch (not shown) could be advantageously provided. to disconnect circuits 48 and 50 from inputs 14, 16 and 18 when the user wishes to use only the main speakers and does not want to hear surrounding sound. It has been found that capacitors are required unpolarized for the decoding circuits of the present invention. Of course, it will be readily understood by those skilled in the art that the coupled pairs of polarized capacitors could be replaced. 20 It should be noted that even when circuits 46, 48 and 50 have been described as separate circuits, those circuits can be advantageously incorporated on a printed circuit board (not shown). As will be understood by an expert in In the art, circuits 46, 48 and 50 illustrated in Figure 2 and described hereinabove are given by way of example only and could be modified without departing from the scope of the present invention. It should also be noted that each circuit includes 5 volume controls accessible to the user to modify the volume of each of the three groups of speakers, ie the main speakers, the secondary speakers and the center speaker. Actually, it has been found that some users prefer to hear the surrounding channels I 10 (reproduced by the secondary speakers) and the center panel (reproduced by the center speaker) at a volume greater or less than what is considered optimal. In addition, since the decoding circuit 10 can be connected to a number of different amplifiers of stereophonic power and a number of different speakers, the separate volume controls help t compensate for those differences. However, a stereophonic post-amplification could be made for a circuit that decodes less expensive surround sound, removing the variable resistors 52, 54, 60, 70 (or alternatively 170, 170 '). Similarly, fuses 72, 74 and 76 could be removed from the circuit since they are provided only for overload protection. It should be noted that such an amplified circuit (not shown) would be less versatile since the user would have no impediment to the control of the three groups of loudspeakers. It should be noted that even when the • »< stereophonic post-amplification for the circuit 5 that decodes the surrounding sound 10 described above includes outputs to the left main speakers, and main right, it will be within the knowledge of one skilled in the art to design a fingerding apparatus (not shown) that does not include those outputs if it was intended that the decoder be used with a power amplifier provided with two pairs of left-right outputs. Actually, a pair of outputs could be directly connected to the main left and right main speakers, while the other pair of outputs could be supplied to the decoding apparatus to produce the secondary left, secondary left and center outputs, as described above. Of course, such a decoding device would be less versatile because that independent control over the signal is not provided to the main loudspeakers and since the circuit would only be useful in the type of power amplifiers mentioned above or with multiple integrated amplifiers provided with a ground connection floating common.

It should also be noted that such stereophonic post-amplification for the circuit decoding surrounding sound 10 can be advantageously packaged in an enclosure provided with conductors suitable for the input and output of the circuit 10 to produce a stereophonic post-amplification for the apparatus decoding surrounding sound. The actuators of the variable resistors 52, 54, 60 and 70 are advantageously positioned so that they are accessible to the user. Alternatively, the decoding circuit 10 could be installed in a conventional power amplifier to produce an amplified surrounding power without requiring the five amplification channels. Finally it should be noted that the output channels 34, 35; 38, 39; and 42, 43, could be provided with suitable switching elements (not shown), allowing the polarity of those output pairs to be reversed. In fact, the selective inversion of those output pairs would allow the listener to design the reproduction of the surrounding sound. As will be appreciated by those skilled in the art, stereophonic post-amplification for the surrounding sound decoding circuit of the present invention has many advantages over stereophonic for the surround sound of the prior art, such as: decoding is performed downstream of the power amplification, allowing the user to conserve their conventional stereo power amplifier; the decoding circuit is compatible with all conventional professional consumer speakers; the decoding circuit is compatible with all conventional professional consumer audio power amplifiers; the decoding circuit allows the user to control their listening experience independently by varying the volume of the three groups of speakers; the decoding is compatible with all the mixed coding standards of two known channels such as, for example, the surround sound of the domestic theater developed by Dolby laboratories, the Pro-Logic ™ technique and the THXMR technique developed by Lucas Arts Entertaiment Co .; the decoding circuit does not require an additional power source; the decoding circuit offers a wide bandwidth to the central and surrounding channels; the decoding circuit can be easily designed to allow an unusual and complex speaker impedance load; the decoding circuit can be easily designed to handle high power signals by providing components that have an adequate power value; the decoding circuit can be easily designed for different applications such as, for example, multiple media computing applications, automotive sound systems, virtual reality applications; and the decoding circuit can be easily designed with a computer controlled interface, to control the separate volumes, if the particular decoding circuit is intended to be used by a computer controlled application. Although the present invention has been described above in the manner of a preferred embodiment thereof, this preferred embodiment may be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims (18)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A stereophonic post-amplification for an apparatus that decodes surrounding sound, comprising: an input for receiving a stereophonic signal amplified in power including a left channel signal and a right channel signal; a first output configured to be connected to the secondary left speaker; a second output configured to be connected to a secondary right speaker; a third output configured to be connected to the center speaker; characterized in that the decoding apparatus comprises: means for decoding secondary channels for decoding a secondary left channel and a secondary right channel for the signals of the left and right channels of the stereophonic signal amplified in power; the secondary left channel is supplied to the first output and the secondary right channel signal is supplied to the second output; and decoding means of the central channel for decoding a central channel signal of the signals of the left and right channels of the amplified stereophonic signal in power; the decoding means of the central channel includes first and second decoupling members, respectively decoupling the signals from the left and right channels, the decoding means of the central channel includes means for combining the signals of the left and right decoupled channels in the signal of the central channel, the central channel is supplied to the third output, whereby the decoupling means of the decoding means of the central channel allow the signals of the left and right channels of the amplified stereophonic signal to be combined without modification of the signals of the original left and right channels

2. A stereophonic post-amplification for a circuit decoding surrounding sound according to claim 1, characterized in that it also comprises: a fourth output configured to be connected to a left main speaker; and a fifth output configured p to be connected to a main right speaker; and volume control means of the main channels to control the amplitude (a) of a left channel signal supplied to the fourth output of the left channel signal, and (b) a right channel signal supplied to the fifth output of the left channel. the output of the right channel.

3. The stereophonic post-amplification for a circuit that decodes surrounding sound according to claim 1 or 2, characterized in that the decoding means of the central channel also includes means for controlling the amplitude of the signal of the central channel.

4. Stereophonic post-amplification for a circuit that decodes surrounding sound according to claim 3, characterized in that the means controlling the amplitude include at least one variable resistance.

5. A stereophonic post-amplification for a circuit decoding surrounding sound according to claim 1 or 2, characterized in that the first and second decoupling means of the central channel respectively include first and second capacitors.

6. The stereophonic post-amplification for a circuit decoding surrounding sound according to claim 5, characterized in that the first decoupling means includes a first resistor connected in series with the first capacitor, and thus connected to the input to receive the channel signal left; the second decoupling means includes a second resistor connected in series with the second capacitor and thus connected to the input to receive the signal from the right channel; the first and second capacitors are interconnected to combine the undocked left channel signal and the uncoupled right channel signal in the center channel signal.

7. Stereophonic post-amplification for a circuit that decodes surrounding sound in accordance with claim 1 or 2, characterized in that the decoding means of the secondary channels include first and second decoupling means, respectively, that uncouple signals from the left and right channels.

8. Stereophonic post-amplification for a circuit that decodes surrounding sound according to claim 7, characterized in that the first and second decoupling means of the secondary channel decoding means include, respectively, first and second capacitors; the first capacitor is connected between the input and the first output; The second capacitor is connected between the input and the second output.

The stereophonic post-amplification for a circuit that decodes surrounding sound according to claim 7, characterized in that each of the first and second outputs includes a ground connection; the secondary decoding means further include a variable resistor connected in series between the ground connections of the first and second outputs.

10. Stereophonic post-amplification for a circuit that decodes surrounding sound according to claim 5, characterized in that the volume control means of the main channels include (a) a first variable resistance connected to both the fourth output and the input for supply the signal from the left channel to the fourth output, and (b) a second variable resistor so connected to both of the fifth output and the input to supply the right channel signal to the fifth output.

11. A central channel decoding circuit for a stereophonic post-amplification for an apparatus that decodes surrounding sound, characterized in that it comprises: an input for receiving a stereophonic signal amplified in power including a signal from the left channel and a signal from the right channel; - an output configured to be connected to a center speaker; and central decoding means for decoding a central channel signal in the signals of the left and right channels of the stereophonic signal amplified in power; the central decoding means includes first and second decoupling means, respectively, which decouple signals from the left and right channels; the decoding means of the center channel includes means for combining the signals of the left and right decoupled channels in the signal of the center channel; the signal of the central channel is supplied to the output; whereby the decoupling means of the decoding means of the central channel allow the signals of the left and right channels of the amplified stereophonic signal to be combined without modifying the signals of the left and right channels.

12. The decoding circuit of the central channel according to claim 11, characterized in that it also comprises means for «Control the amplitude of the central channel signal.

13. The decoding circuit of the central channel according to claim 12, characterized in that the means controlling the amplitude include at least one variable resistance.

14. The decoding circuit of the central channel 10 according to claim 11, characterized in that the first and second decoupling means include, respectively, first and second capacitors.

15. The decoding circuit of the central channel 15 according to claim 14, characterized in that the first decoupling means includes a first resistor connected in series with the first capacitor, and thus connected to the input to receive the signal from 20 left channel; the second decoupling means includes a second resistor connected in series with the second capacitor and thus connected to the input to receive the signal from the right channel; the first and second capacitors are interconnected to 25 combine the undocked left channel signal and the uncoupled right channel signal in the center channel signal.

16. The channel decoding circuit (central according to claim 15, 5 characterized in that it also comprises means for controlling the central amplitude, the means for controlling the amplitude have at least one variable resistance.

17. The decoding circuit of the central channel according to claim 16, 10 characterized in that at least one of the variable resistance includes a variable resistance provided between the interconnection of the first and second capacitors at the output.

18. The decoding circuit of the central channel 15 according to claim 16, characterized in that at least one variable resistor includes a first variable resistor interconnected in series between the first resistor and the first capacitor, and the second variable resistor 20 interconnected in series between the second resistance and the second capacitor.