METHOD FOR PREPARING A STEREOPHONY SIGNAL FOR MONOPHONIC LISTENING

Abstract

Method (100) of processing a stereophonic input signal (SSTER) comprising a left channel (LIN) and a right channel (RIN), comprising the steps of generating a center channel (Mid) and a first side channel (Side(L), Side(R)), the center channel being representative of a sum of the left channel (LIN) and the right channel (RIN) and the first side channel (Side(L), Side(R)) being representative of a subtraction of one of the left channel (LIN) and the right channel (RIN) from the other of the left channel (LIN) and the right channel (RIN); shifting the phase of the first side channel (Side(L)) by 90° in a first direction to obtain a first out-of-phase side channel (Sh_Side(L)); and generating a first monophonic output channel (SRMS) representing a sum of the center channel (Mid) and the first out-of-phase side channel (Sh_Side(L)). Figure to be published with the abbreviation: Fig. 3

Description

Title of the invention: METHOD FOR PREPARING A STEREOPHONIC SIGNAL FOR MONOPHONIC LISTENING TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method for processing a stereophonic signal, in the context of monophonic listening. TECHNOLOGICAL BACKGROUND

[0002] The recording of a piece of music is most often carried out in such a way as to be able to reproduce this piece by means of a stereophonic installation, that is to say designed to reconstruct the spatial distribution of the sound sources during recording (spatialization). This so-called "stereophonic" effect is usually obtained by recording a sound scene by means of two microphones, each microphone being used to generate respectively one of two sound channels, conventionally called the left channel and the right channel. Thus, a piece of music is often found in so-called stereophonic formats, in which an audio signal is composed of two channels.

[0003] These stereo formats are intended for stereo reproduction, with each channel being reproduced by a dedicated loudspeaker of the stereo system. However, a user may wish to reproduce a piece in a stereo format in a monophonic manner. This situation is commonplace and occurs, for example, when the user only has a monophonic reproduction system such as a smartphone or a wireless speaker, which often only have one loudspeaker.

[0004] In such a situation, a usual solution is to merge the two channels by summation and reproduce the signal obtained by the single loudspeaker. This operation, however, results in a loss of information corresponding to what is referred to in the field of audio signal processing as the out-of-phase content of the signal.

[0005] This loss of information can be explained with the help of [Fig.l] and [Fig.2]. These figures each illustrate two signals: a signal SI and a signal S2 corresponding respectively to the two channels of a stereophonic signal. A third signal S1+S2 represents the sum of these two signals.

[0006] In the particular case illustrated by [Fig.l], the two signals S1 and S2 are identical and in phase. Their sum therefore corresponds to a signal S1+S2 with an amplitude twice that of the signals S1 and S2.

[0007] In the particular case illustrated by [Fig.2], the two signals SI and S2 are identical, but in phase opposition with respect to each other, that is to say with respective phases shifted by 180° with respect to each other. Their sum is therefore zero.

[0008] In the situation illustrated by [Fig.2], summing the signals S1 and S2 leads to a loss of information, that of the out-of-phase content of the stereophonic signal. However, this out-of-phase content is responsible for our perception of stereo and contains critical sound information that disappears in traditional monophonic reproduction of a stereophonic signal.

[0009] In a general case, the signals S1 and S2 are not simply either in phase or out of phase, but comprise information represented by components of the in-phase signals and other information represented by components of the out-of-phase signals. The level of information loss will depend on each stereophonic signal, and it may be the responsibility of a sound engineer to ensure what is called "mono compatibility" of the stereophonic signal, i.e. to prepare a stereophonic signal in such a way as to limit information loss when it is reproduced in monophonic. Imposing this compatibility limits the freedom of action of the sound engineer. Furthermore, a significant degradation in the audio quality of a stereophonic signal reproduced in monophonic compared to the reproduction of this same signal in stereophonic will generally be observed. Disclosure of the invention

[0010] An object of the invention is a method of processing a stereophonic input signal, comprising in-phase content and out-of-phase content, and generating a monophonic output signal comprising out-of-phase content of the input stereophonic signal.

[0011] To achieve this aim, a first aspect of the invention is a method for processing a stereophonic input signal comprising a left channel and a right channel, comprising the steps of generating a center channel and a first side channel, the center channel being representative of a sum of the left channel and the right channel and the first side channel being representative of a subtraction of one of the left channel and the right channel from the other of the left channel and the right channel; phase shifting the first side channel by 90° in a first direction to obtain a first phase-shifted side channel; and generating a first monophonic output channel representative of a sum of the center channel and the first phase-shifted side channel.

[0012] This method makes it possible to generate a signal suitable for monophonic sound reproduction comprising out-of-phase content of the original stereophonic signal. The resulting sound reproduction is richer in information than a conventional monophonic signal, in which this out-of-phase content is absent, resulting in an excellent musicality of sound reproduction than if a conventional monophonic signal were used. The sonic balance achieved during the various stages of production of the original stereophonic signal and the corresponding emotion are preserved even when switching to monophonic listening.

[0013] Furthermore, the generation of a monophonic signal according to the invention allows that, whatever the position of a listener in relation to a sound source reproducing this signal, the listener perceives the out-of-phase content in the same conditions as if he were located at the ideal listening point in a stereo configuration (apart from spatialization), which is the vertex of an equilateral triangle with a pair of speakers at the other two vertices. An advantage of the technique according to the invention is therefore the mobility for the listener, who is not constrained to a fixed position, predetermined by the position of the two speakers. This aspect is particularly advantageous compared to the situation of a portable speaker whose left and right loudspeakers are very close together (less than 90 cm, the minimum distance commonly accepted for loudspeakers in a stereophonic configuration), in which the listener can hardly stand at the ideal listening point.

[0014] Thus, by switching from a conventional stereo mode to a monophonic mode according to the invention, the user can freely choose between (i) stereophonic listening with spatialization information, a case in which he is forced to remain at a fixed point so as to form an equilateral triangle with a pair of speakers for optimal listening, and (ii) a monophonic mode with out-of-phase content made audible, a case in which the listener is mobile since the listening quality does not depend on his location.

[0015] According to additional non-limiting characteristics of the first aspect of the invention, considered individually or in any technically feasible combination:

[0016] - the treatment method according to the invention may further comprise the steps of generating a second side channel of opposite polarity to the first side channel; phase shifting the second side channel by 90° in a second direction opposite to the first direction to obtain a second phase-shifted side channel; generating a second monophonic output signal representative of a sum of the center channel and the second phase-shifted side channel, wherein the first monophasic output channel and the second monophonic output channel form a two-channel monophonic output signal; and

[0017] - the first side channel may be representative of a subtraction in which one subtracts the right channel from the left channel, and the first side channel is shifted by +90°.

[0018] The invention extends to:

[0019] - a computer program comprising instructions which, when the program is executed by a digital computer, leading the latter to apply to a stereophonic input signal the steps of the method according to the invention;

[0020] - a computer-readable medium comprising instructions which, when executed by a digital computer, lead the latter to apply to a stereophonic input signal the steps of the method according to the invention; and

[0021] - an electronic chip configured to implement the steps of the method according to the invention.

[0022] The invention extends to an electronic device configured to implement the steps of the method according to the invention by software or by hardware.

[0023] According to additional non-limiting characteristics of the first aspect of the invention, considered individually or in any technically feasible combination:

[0024] - the electronic device according to the invention can be configured to switch from a first mode of operation in which the device generates the first monophonic output channel to a second mode of operation in which the device generates a monophonic output channel representative of the center channel;

[0025] - the electronic device according to the invention can be configured so that content out-of-phase stereo input signal is absent from the mono output channel representative of the center channel;

[0026] - the electronic device according to the invention may comprise an interface of control configured to switch the device from the first mode of operation to the second mode of operation;

[0027] - the electronic device according to the invention may comprise an interface of control configured to switch the device from the first operating mode to an operating mode in which the first monophonic output channel is representative of the first phase-shifted side channel excluding the center channel;

[0028] - the electronic device according to the invention can be chosen from a smartphone, a monophonic loudspeaker, a sound recording broadcasting system, and a centralization module (Cent) configured to distribute the first monophonic output channel (L0Ut) to a plurality of loudspeakers. BRIEF DESCRIPTION OF THE FIGURES

[0029] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0030] [Fig.l] [Fig.l] illustrates the concept of “phased content”;

[0031] [Fig.2] [Fig.2] illustrates the concept of “out-of-phase content”;

[0032] [Fig.3] [Fig.3] illustrates a first mode of operation of a first mode of implementation of a method according to the invention;

[0033] [Fig.4] [Fig.4] illustrates a second mode of operation of the first mode of implementation;

[0034] [Fig.5] [Fig.5] illustrates a first mode of operation of a second mode of implementation of a method according to the invention;

[0035] [Fig.6] [Fig.6] illustrates a second mode of operation of the second mode of implementation;

[0036] [Fig.7] [Fig.7] illustrates a third mode of operation of the second mode of implementation;

[0037] [Fig.8] [Fig.8] illustrates a variation of the second mode of implementation;

[0038] [Fig.9] [Fig.9] illustrates a first mode of operation of a third mode of implementing a method according to the invention;

[0039] [Fig. 10] [Fig. 10] illustrates a second mode of operation of the third mode of implementation;

[0040] [Fig. 11] [Fig. 11] illustrates a first mode of operation of a fourth mode of implementation of a method according to the invention;

[0041] [Fig. 12] [Fig. 12] illustrates a second mode of operation of the fourth mode of implementation;

[0042] [Fig. 13] [Fig. 13] illustrates a first mode of operation of a fifth mode of implementation of a method according to the invention;

[0043] [Fig. 14] [Fig. 14] illustrates a second mode of operation of the fifth mode of implementation;

[0044] [Fig. 15] [Fig. 15] illustrates a third mode of operation of the fifth mode of implementation;

[0045] [Fig. 16] [Fig. 16] represents a first device configured to implement a method according to the invention;

[0046] [Fig. 17] [Fig. 17] represents a second device configured to implement a method according to the invention; and

[0047] [Fig. 18] [Fig. 18] represents a system configured to implement a method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0048] The invention aims to improve the monophonic sound reproduction of a stereophonic signal. To this end, the inventors have developed a method for preserving the out-of-phase content of the stereophonic signal in a signal derived therefrom, suitable for high-quality monophonic sound reproduction.

[0049] First mode of implementation

[0050] Figures 2 and 3 illustrate a first mode of implementation of a method 100 according to the invention. This first mode of implementation includes three operating modes.

[0051] This method is a processing of an input SSTer stereophonic signal comprising a left channel L1N and a right channel R1N with the aim of transforming it into an output signal suitable for reproduction in an improved monophonic mode called RMS mono mode for Real Mono Sound stereophonic, for reproduction in a conventional stereophonic mode (two operating modes illustrated by [Fig.3]), or for reproduction in a conventional monophonic mode (illustrated by [Fig.4]).

[0052] [Fig.3] illustrates a first mode of operation of the second embodiment, making it possible to obtain an output signal Srms suitable for reproduction according to the RMS mode of improved monophonic reproduction; suitable for reproduction by means of a monophonic sound system. The output signal SRMS includes the out-of-phase content of the input stereo signal Sster-

[0053] At a first processing stage Stl, the stereophonic input signal Sster is transformed or encoded into a so-called Mid / Side signal by means of a functional block MS-Enc. At this stage, the information contained in the stereophonic signal Sster can be distributed into three channels designated Mid, Side(L) and Side(R).

[0054] The Mid channel is a signal representative of the information located in the middle of the sound scene represented by the stereophonic input signal Sster and corresponds to the sum of the two channels L1N and R1N. The Mid channel is representative of the sum of the two channels LIX and R^ and can be calculated by applying a summation function to these two channels by means of a summation functional block Suml configured to sum the signals supplied to it as input and provide their sum as output, here such that Mid = LIN + RIN.

[0055] The Side(L) channel is a signal representative of the information located on the sides of the sound scene represented by the stereophonic input signal SSTer and corresponds to the difference of the two channels L1N and R1N. The Side(L) channel is representative of the difference between the two channels L1N and R1N, and can be calculated by applying to these two channels a subtraction function by means of a Diffl(L) functional block configured to perform a difference between two signals supplied to it as input and provide their difference as output, such that Side(L) = LIN- RIN.

[0056] The Side(R) channel is a signal representative of the information located on the sides of the sound scene represented by the stereophonic input signal Sster and corresponds to the difference of the two channels R^ and L1N. The Side(R) channel is representative of the difference between the two channels L1N and R1N, and can be calculated by applying to these two channels a subtraction function by means of a Diffl(R) functional block configured to perform a difference between two signals supplied to it in input and provide their difference at the output, such that Side(R)= RIN- LIN. We can thus consider that the Side(R) channel and the Side(L) channel are of opposite polarities.

[0057] The functions Suml, Diffl(L) and Diffl(R) are here part of the MS-Enc functional block, which can be implemented according to conventional techniques for processing a stereophonic audio signal.

[0058] The Mid channel is here split (the functional block Sum1 has two identical Mid channels as output) in anticipation of the processing carried out subsequently: anticipating the rest of the explanations, the Mid signal will be combined with two other signals. To maintain the relative amplitudes of these signals throughout the processing, it is necessary to balance their amplitudes, which is represented in the figures by a splitting of the Mid channel to avoid reducing its amplitude by two when it is divided into two identical parts. Of course, this is a representation given for a particular implementation of the method, and alternatives with equivalent effect will obviously appear to those skilled in the art.Generally speaking, in this specification, signal transmissions and combinations are described, and those skilled in the art will understand that, depending on the type of implementation actually practiced, it may be necessary to balance the amplitudes of the signals involved. Such adjustments are generally omitted in order to keep the specification concise.

[0059] The signals generated by the first processing stage are transmitted to a second processing stage St2 via two selection functional blocks SelL and SelR interposed between the functional blocks Diffl(L) and Diffl(R) and the functional blocks Ph+ and Ph-, respectively.

[0060] In the second processing stage, phase shift functions are applied to the Side(L) and Side(R) channels by means of a Ph-Shift phase shift functional block. In the present embodiment, phase shifts of +90° and -90° are applied to the Side(L) and Side(R) channels to obtain the Sh_Side(L) and Sh_Side(R) channels by means of Ph+ and Ph- phase shift functional blocks, respectively, each configured to apply a phase shift to a signal provided as input and provide the phase-shifted signal as output. By their construction, the Sh_Side(L) and Sh_Side(R) channels are identical: Sh_Side(L) = Sh_Side(R).

[0061] It is possible to apply, conversely, phase shifts of -90° and +90° respectively to the Side(L) and Side(R) channels. However, the inventor has observed a loss of sound brightness on rare audio contents when phase shifts of -90° and +90° are applied respectively to the Side(L) and Side(R) channels. Thus, from the inventor's experience, the results are in the vast majority of cases more satisfactory in terms of listening quality, and in particular sound brightness, when phase shifts of +90° and -90° are respectively applied to the Side(L) channels. and Side(R). For this reason, it is this latter configuration which is illustrated by [Fig.3] and which is used for the description of the present mode of implementation.

[0062] The signals processed by the second stage are transmitted to a first recombination stage Red.

[0063] At the Red recombination stage, two summations of the Mid, Sh_Side(L) and Sh_Side(R) channels are carried out to obtain two channels A1 and A2 at the stage output.

[0064] The first channel Al is representative of the sum of the two channels Mid and Sh_Side(L) and can be calculated by applying to these channels a summation function by means of a summation functional block SumRecL configured to sum the signals supplied to it as input and provide their sum as output, such that Al = Mid + Sh_Side(L) = LIN+ RIN+ Sh_Side(L).

[0065] The second channel A2 is representative of the sum of the two channels Mid and Sh_Side(R) can be calculated by applying to these channels a summation function by means of a summation functional block SumRecR configured to sum the signals supplied to it as input and provide their sum as output, such that A2 = Mid + Sh_Side(R) = L^ + R^ + Sh_Side(R).

[0066] The channels generated at the first recombination stage Red are transmitted to a second recombination stage Rec2.

[0067] At the recombination stage Rec2, a summation and two subtractions of the channels A1 and A2 are carried out to obtain three channels B1, B2 and B3.

[0068] The first channel B1 is representative of the sum of the two channels A1 and A2 and can be calculated by applying a summation function to these channels by means of a summation functional block Sum2(L) configured to sum the signals supplied to it as input and provide their sum as output, such that Bl = A1 + A2 = 2(L1N+ R1N + Sh_Side(L)).

[0069] The second channel B2 is representative of the difference between the two channels A1 and A2, and can be calculated by applying a subtraction function to these two channels by means of a functional block Diff2(L) configured to perform a difference between two signals supplied to it as input and provide their difference as output, such that B2 = A1- A2 = Sh_Side(L) - Sh_Side(R), i.e. zero in the case modeled by [Fig.2].

[0070] The third channel B3 is representative of the difference between the two channels A1 and A2, and can be calculated by applying to these two channels a subtraction function by means of a functional block Diff2(R) configured to perform a difference between two signals supplied to it as input and provide their difference as output, such that B3 = A2- A1 = Sh_Side(R) - Sh_Side(L), i.e. zero in the case modeled by [Fig.2].

[0071] The functions Sum2, Diff2(L) and Diff3(R) can be part of a second MS-Enc functional block identical to the MS-Enc functional block of the first processing stage Stl. These two functional blocks apply the same operations to the signals which are respectively supplied to them as input.

[0072] The channels B1, B2 and B3 generated at the second recombination stage Rec2 are transmitted to a third processing stage St3 via switching functional blocks ComL and ComR, connecting the functional blocks Diff2(L) and Diff2(R) to two summing blocks Sum2(L) and Sum2(R) of the third processing stage, respectively.

[0073] In the third processing stage St3, two equal output channels L0Ut and ROut are generated so as to be suitable for transmission to a monophonic sound reproduction system, by means of a functional block MS-Dec, on the basis of the channels Bl, B2 and B3. These two channels L0Ut and R0Ut form the output signal Srms-

[0074] The output channel L0Ut is representative of the sum of the two channels Bl and B2, and can be calculated by applying to these channels a summation function by means of the summation functional block Sum2(L) configured to sum the signals supplied to it as input and provide their sum as output, such that LOut = B1 + B2 = 2(L1N + Rin + Sh_Side(L)).

[0075] The output channel ROut is representative of the sum of the two channels B1 and B3 and can be calculated by applying to these channels a summation function by means of the summation functional block Sum2(R) configured to sum the signals supplied to it as input and provide their sum as output, such that ROut = 2(L1N + R^ + Sh_Side(R)).

[0076] The two output channels L0Ut and ROut are equal, the Sh_Side(L) and Sh_Side(R) channels being identical: Sh_Side(L) = Sh_Side(R), and can therefore be transmitted to a monophonic reproduction sound system without additional processing. The phase changes applied to the Side(L) and Side(R) channels, which contain out-of-phase information content, made it possible to equalize these signals, so that the so-called "out-of-phase" information content of the Side(L) and Side(R) channels is no longer out of phase at the phase-shifted channels Sh_Side(L) and Sh_Side(R) and the information loss phenomenon described using [Fig.2] is avoided.

[0077] The monophonic signal Srms formed by the two output channels L0Ut and R0Ut can be transmitted to, for example, a conventional monophonic loudspeaker, equipped with a system for converting a two-channel stereophonic input signal to a one-channel monophonic signal which will actually be reproduced by a loudspeaker. Conventionally, the merging of the two channels leads to the loss of the out-of-phase information content as explained above. On the other hand, when the stereophonic signal has been processed according to the present operating mode, the information content is no longer out-of-phase and is therefore not lost when the monophonic loudspeaker operates the conversion of the monophonic signal Srms which is supplied to it as input. The sound reproduction of the signal Srms has a much richer content and closer to the ear to the original SSTer stereophonic signal than the reproduction of a conventional monophonic signal obtained by a simple fusion of the channels of the original stereophonic signal.

[0078] [Fig.3] also illustrates a second mode of operation of the first mode of implementation of the invention, making it possible to find at the processing output an Sstereo signal identical to the original SSTer signal.

[0079] This second operating mode differs from the first operating mode in the following respect: instead of transmitting the Side(L) and Side(R) channels to the second processing stage St2 and therefore to the Ph+ and Ph- blocks, the two selection functional blocks SelL and SelR transmit these two channels to the Red recombination stage via simple derivations DerL and DerR connected to the SumReciL and SumReciR functional blocks, respectively, without processing or modification to the content of the transmitted signals, and in particular without applying a phase shift to these channels. Alternatively, the Ph+ and Ph- blocks could be deactivated so as to transmit the channels supplied to them without modifying them. Apart from this identical transmission of the channels from Diffl(L) and Diffl(R) blocks to the Red stage, the first and second operating modes are identical.

[0080] Thus, the channels A1 and A2, B1 to B3, and LOut and ROut are, in this second operating mode, obtained on the basis of the Mid, Side(L) and Side(R) channels, instead of the Mid, Sh_Side(L) and Sh_Side(R) channels for the first operating mode, the same operations being applied respectively to these channels as in the first operating mode. Thus, we obtain A1 = 2L1N; A2 = 2RIX; B1 = 2(L1N+R1N); B2 = L1N-R1N; B3 = R1N-L1N; L0Ut= 2L1n; and ROut= 2R1n. In this second operating mode, the two output channels L0Ut and R0Ut form a stereo signal at the output of the third processing stage. This Sstereo signal is a stereophonic signal, comprising two differentiated channels containing between them an information content identical in substance to the original SSTer signal and sufficient to reconstruct the spatial distribution of the sound sources during recording.

[0081] [Fig.4] illustrates a third mode of operation of the first mode of implementation of the invention, making it possible to obtain an output signal SMONo suitable for possible reproduction by means of a monophonic sound system but not including the out-of-phase content of the original stereophonic signal, unlike the signal SRMS of the first mode of operation.

[0082] This third mode of operation differs from the first mode of operation in the following respect: the switching functional blocks ComL and ComR are configured so as to prevent the transmission of the output channels of the blocks Diff2(L) and Diff2(R) to the blocks Sum2(L) and Sum2(R). Apart from this respect, the first and second modes of operation are identical.

[0083] Thus, at the output of the Sum2(L) and Sum2(R) functional blocks, the L0Ut and R0Ut channels are equal and each equal the Mid channel: L0Ut= Rout= Mid = LIX + R^. Whether the Ph-Shift functional block is deactivated or left in operation does not significantly affect this second operating mode: a SMOno signal is formed from the two L0Ut and Roui* channels

[0084] The SMOno signal can be supplied as an input to a monophonic speaker. Since the out-of-phase content of the SSTer stereophonic signal is absent from the Mid channel, it is therefore also absent from the sound reproduction produced by the speaker, which therefore has a reduced information content compared to the original SSTer signal and compared to the Srms signal of the first operating mode.

[0085] The Ph+, Ph-, ComL and ComR blocks can be controlled conventionally by a user to compare the sound reproductions of the different operating modes and observe the relative richness of content, with in particular the Srms and Sstereo signals much richer in information than the S signal MONO*

[0086] Second mode of implementation

[0087] Figures 5 to 8 illustrate a second mode of implementation of a method according to the invention. This second mode of implementation includes three operating modes, respectively illustrated by Figures 5 to 7, and a variant illustrated by [Fig.8].

[0088] This method is a processing of an input SSTer stereophonic signal comprising a left channel L1N and a right channel R1N with the aim of transforming it into an output signal suitable for stereophonic reproduction ([Fig.7]) or monophonic reproduction, and in the latter case for reproduction according to a conventional monophonic mode ([Fig.6]) or an improved monophonic mode ([Fig.5]) called RMS mono mode for Real Mono Sound.

[0089] [Fig.5] illustrates a first mode of operation of the second mode of implementation, making it possible to obtain an output signal Srms suitable for possible reproduction by means of a monophonic sound system and including the out-of-phase content of the stereo input signal SSTer*

[0090] This implementation mode includes the first, second and third processing stages St1, St2 and St3 of the first implementation mode, but the first recombination stage Red and the second recombination stage Rec2 are omitted. Reference may therefore be made to the description of the first implementation mode for its common elements with the second implementation mode.

[0091] Here, the output channels of the Suml block are directly transmitted to the Sum2(L) and Sum2(R) blocks and the output channels of the Ph+ and Ph- blocks are directly transmitted to the ComL and ComR blocks, considered as part of the third stage of St3 treatment, respectively.

[0092] In the third processing stage, the equal output channels L0Ut and R0Ut are generated so as to be suitable for transmission to a monophonic sound reproduction system, by means of a functional block MS-Dec, on the basis of the signals Mid, Sh_Side(L) and Sh_Side(R). These two channels L0Ut and R0Ut form the output signal Srms-

[0093] The output channel L0Ut is representative of the sum of the two channels Mid and Sh_Side(L) and can be calculated by applying a summation function to these channels using the summation functional block Sum2(L) configured to sum the signals supplied to it as input and provide their sum as output, such that L0Ut = Mid + Sh_Side(L).

[0094] The output channel R0Ut is representative of the sum of the two channels Mid and Sh_Side(R) and can be calculated by applying a summation function to these channels using the summation functional block Sum2(R) configured to sum the signals supplied to it as input and provide their sum as output, such that ROut = Mid + Sh_Side(R).

[0095] Two switching functional blocks, ComL and ComR, are configured to, in this first operating mode, transmit the channels Sh_Side(L) and Sh_Side(R) to the functional blocks Sum2(L) and Sum2(R), respectively.

[0096] As for the first mode of operation of the first embodiment, the two output channels L0Ut and R0Ut are equal and form the monophonic signal Srms which can be transmitted to a monophonic reproduction sound system without additional processing. The phase changes applied to the Side(L) and Side(R) channels, which contain out-of-phase information content, made it possible to equalize these signals, so that the so-called "out-of-phase" information content of the Side(L) and Side(R) channels is no longer out-of-phase at the phase-shifted channels Sh_Side(L) and Sh_Side(R) and the information loss phenomenon described with the aid of [Fig.2] is avoided. The monophonic signal Srms has information content enriched with the out-of-phase content compared to a conventional monophonic signal, in which the out-of-phase content is lost.

[0097] [Fig.6] illustrates a second mode of operation of the second mode of implementation of the invention, making it possible to obtain an SMono output signal suitable for possible reproduction by means of a monophonic sound system but not including the out-of-phase content of the original stereophonic signal, unlike the SRMs signal of the first mode of operation.

[0098] This second mode of operation differs from the first mode of operation in the following respect: the switching functional blocks ComL and ComR are configured so as to prevent the transmission of the channels Sh_Side(L) and Sh_Side(R) to the Sum2(L) and Sum2(R) function blocks. Apart from this point, the first and second modes of operation are identical. Whether the Ph-Shift function block is in operation or not does not affect the second mode of operation.

[0099] Thus, at the output of the functional blocks Sum2(L) and Sum2(R), the channels L0Ut and R0Ut are equal and each equal the Mid channel: L0Ut = Roui = Mid. The signal SMOno is formed from the two channels L0Ut and ROut, and can be supplied at the input of a monophonic speaker. The out-of-phase content of the stereophonic signal SSTer being absent from the Mid channel, it is therefore also absent from the sound reproduction produced by the speaker, which therefore has a reduced information content compared to the original SSTer signal.

[0100] [Fig.7] illustrates a third mode of operation of the second mode of implementation of the invention, making it possible to find at the processing output a stereo S signal identical to the original SSTer signal.

[0101] This third mode of operation differs from the first mode of operation in the following respect: the Ph-Shift functional block is deactivated, transmitting the Side(L) and Side(R) channels from the first processing stage to the third processing stage without applying a phase shift to these channels. Apart from this point, the first and third modes of operation are identical.

[0102] Thus, at the processing output, the output channel LOut is representative of the sum of the two channels Mid and Side(L) and can be calculated by applying a summation function using the functional block Sum2(L) to these two channels, such that L0Ut = Mid + Side(L).

[0103] Similarly, the output channel ROut is representative of the sum of the two channels Mid and Side(R) and can be calculated by applying a summation function using the functional block Sum2(R) to these two channels, such that ROut = Mid + Sh_Side(R).

[0104] Thus, the SSTereo signal at the output of the third processing stage is a stereophonic signal, comprising two differentiated channels containing between them sufficient informative content to reconstruct the spatial distribution of the sound sources during recording.

[0105] [Fig.8] illustrates a variant of the second mode of implementation applied to the third mode of operation, also making it possible to find at the processing output an SSTereo signal identical to the original SSTer signal.

[0106] With the application of this variant, the fourth mode of operation changes from its version illustrated by [Fig.7] in the following respect: instead of deactivating the Ph-Shift functional block, the Ph+ and Ph- functional blocks it contains are bypassed when a stereo output is desired.

[0107] More specifically, as for the implementation mode illustrated by [Fig.4], the two selection functional blocks SelL and SelR are interposed between the blocks Diffl(L) and Diffl(R) functional blocks and the Ph+ and Ph- functional blocks, respectively. These functional blocks are configured to transmit the Side(L) and Side(R) channels to the second processing stage when the Srms signal is desired as in the first operating mode. On the other hand, in the present operating mode where the SSTereo signal is desired as in the third operating mode, these functional blocks are configured to transmit the Side(L) and Side(R) channels directly to the third processing stage to apply the phase shifts of the second processing stage by means of DerL and DerR derivations, respectively.

[0108] This mode of operation is particularly suitable for a hardware implementation of the method, but also represents an implementation of the processing applied in software to the original SSTer stereo signal.

[0109] Third mode of implementation

[0110] Figures 9 and 10 illustrate a third mode of implementation of a method according to the invention. This third mode of implementation includes two operating modes, respectively illustrated by Figures 9 and 10.

[0111] The third mode of implementation is particularly suited to minimal digital processing during a software implementation, which has the advantage of limiting the consumption of resources (computing time, battery) of the device used to run the software implementation of the method.

[0112] This third mode of implementation differs from the second mode of implementation on the following points: (i) the Side(R) channel is transmitted directly to the third processing stage, without undergoing a phase shift and this whatever the operating mode considered, (ii) the Sh_Side(L) channel is amplified by means of a functional block Mult which is configured to multiply by two the amplitude of a signal which is supplied to it at the input and which at the output provides the amplified signal Ash_Side(L), (iii) the third processing stage comprises two switching functional blocks Com3 and Com4 responsible for controlling the transmission of the ASh_Side(L) channel and the Side(R) channel to the Sum2(R) functional block, respectively. Apart from these three points, the second and third modes of implementation are identical and one can therefore refer to the explanations concerning the second mode of implementation.

[0113] [Fig.9] illustrates a first mode of operation of this third mode of implementation, making it possible to obtain an SRMS output signal suitable for possible reproduction by means of a monophonic sound system and including the out-of-phase content of the stereo input signal Sster-

[0114] The Ph+ functional block can be implemented by means of a phase variation function by convolution of the Side(L) channel with an impulse response defined so that the convolution generates the phase-shifted Sh_Side(L) channel of the Side(L) channel of 90°, and more specifically of +90° in this example.

[0115] The Mid channel is transmitted to the inputs of the two functional blocks Sum2(L) and Sum2(R), the ASh_Side(L) channel is transmitted to the Sum2(L) functional block, and the switching functional block Com3 transmits the ASh_Side(L) channel to the Sum2(R) functional block while the switching functional block Com4 blocks the transmission of the Side(R) channel to the Sum2(R) functional block. The ASh_Side(L) channel is divided into two equal parts and combined with the two Mid signals in such a way that the relative amplitude between the Mid and Side(L) signals on the one hand, and the relative amplitude between the two Mid channels and each of the two signals coming from the Ash_Side(L) channel and supplied as inputs to the Sum2(L) and Sum2(R) blocks on the other hand, are equal, maintaining the original balance between the different information contained in the stereophonic signal S STER- fO 1 16] Thus, the output channels L0Ut and ROut are with L0Ut = Rout = Mid + Sh_Side(L), each output channel being obtained by the summation of the two channels Mid and Ash_Side(L). The output signal Srms therefore comprises two identical channels, with the advantages and applications already mentioned for the SRMs signal of the first and second modes of implementation.

[0117] [Fig. 10] illustrates a second mode of operation of the third mode of implementation of the invention, making it possible to find at the processing output a stereo signal S identical to the original Sster signal.

[0118] This second mode of operation differs from the first mode of operation in the following respects: (i) the Ph-Shift functional block is disabled, transmitting the Side(L) and Side(R) channels from the first processing stage to the third processing stage without applying any phase shift or amplification to these channels, (ii) the switching functional block Com3 is configured to block the transmission of the Side(L) channel to the Sum2(R) functional block and the switching functional block Com4 is configured to transmit the Side(R) channel to the Sum2(R) functional block.

[0119] Thus, we find the situation of the third operating mode of the second implementation mode, illustrated by [Fig.7]: L0Ut = Mid + Sh_Side(L) and R0Ut = Mid + Sh_Side(R), the SSTereo signal at the output of the third processing stage is a stereophonic signal, comprising two differentiated channels containing between them sufficient informative content to reconstruct the spatial distribution of the sound sources during recording.

[0120] Of course, instead of deactivating the Ph-Shift block, one could proceed as described in the operating variant of the second mode of implementation, illustrated by [Fig.8], in which selection functional blocks and derivations are used to transmit the Side(L) and Side(R) channels to the third processing stage without a phase shift being applied to them, i.e. by bypassing the blocks Ph+ and Ph- phase shift functionals.

[0121] Fourth mode of implementation

[0122] Figures 11 and 12 illustrate a fourth mode of implementation of a method according to the invention. This fourth mode of implementation includes two operating modes, respectively illustrated by Figures 11 and 12.

[0123] The fourth embodiment is optimized for a device that is not designed to reproduce a stereophonic sound signal. This is for example the case of a monophonic speaker, for example a so-called “Bluetooth” speaker, configured to reproduce a sound signal by means of a single loudspeaker. In such a case, the loss of the possibility of providing a stereophonic signal at the processing output is not a problem, and the processing can therefore be simplified. In particular, it is not necessary to maintain an operating mode allowing a stereophonic signal to be produced.

[0124] Thus, this fourth mode of implementation differs from the third mode of implementation on the following points: (i) the functional block MS-Enc does not include the functional block Diffl(R), (ii) the functional block MS-Dec does not include the switching blocks ComL, ComR, Com3 and Com4, (iii) a switching block Com5 is configured to control the transmission of a signal originating from the functional block Diffl(L) to the third processing stage. Apart from these points, the third and fourth modes of implementation are identical and reference may be made to the description of the third mode of implementation.

[0125] In this embodiment, switching block Com5 is configured to control the transmission of the Side(L) channel to the Ph-Shift functional block, but it could be located at another level, such as between the Ph-Shift functional block and the MS-Dec functional block, the main thing being to ensure that only the Mid signal is transmitted to the Sum2(L) and Sum2(R) functional blocks.

[0126] [Fig. 11] illustrates a first mode of operation of this fourth mode of implementation, making it possible to obtain an SRMS output signal suitable for possible reproduction by means of a monophonic sound system and including the out-of-phase content of the SSTer stereo input signal.

[0127] This first mode of operation is similar to the first mode of operation of the third implementation mode, illustrated by [Fig.9]: the Side(L) channel is transmitted to the Ph-Shift functional block by means of the Com5 functional block, and the Ash_Side(L) channel is transmitted to the Sum2(R) functional block.

[0128] Consequently, the output channels LOut and ROut are identical with LOut = Roui = Mid + Sh_Side(L), each output channel being obtained by the summation of the two channels Mid and Ash_Side(L). The SRMs output signal therefore comprises two identical channels, with the advantages and applications already mentioned for the Skms signal of the first and second modes of implementation.

[0129] [Fig. 12] illustrates a second mode of operation of the fourth embodiment of the invention, making it possible to obtain an SMOno output signal suitable for reproduction by means of a monophonic sound system but not including the out-of-phase content of the original stereophonic signal, unlike the SRMS signal of the first mode of operation.

[0130] The functional block Com5 is configured to block the transmission of the Side(L) channel to the second and third processing stages. Consequently, the functional blocks Sum2(L) and Sum2(R) are only supplied by the Mid channel, and at the output of the functional blocks Sum2(L) and Sum2(R), the channels L0Ut and ROut are equal and each equal the Mid channel: L0Ut = Roui = Mid. The signal SMOno is formed by the two channels L oui and Rout, and can be supplied at the input of a monophonic speaker. The out-of-phase content of the stereophonic signal SSTer being absent from the Mid channel, it is therefore also absent from the sound reproduction produced by the speaker, which therefore has a reduced information content compared to the original Sster signal and the signal Srms-

[0131] Fifth mode of implementation

[0132] Figures 13 and 14 illustrate a fifth embodiment of a method according to the invention. This fifth embodiment includes two operating modes, respectively illustrated by Figures 13 and 14.

[0133] This fifth embodiment is a variant of the fourth embodiment, simplified in the following points: (i) the functional block Suml has only one Mid channel as output, (ii) the functional block Ph-Shift does not include the functional block Mult and (iii) the functional block MS-Dec does not include the functional block Sum2(R). In addition, a switching block Com6 is configured to control the transmission of the Mid channel to the functional block Sum2(L) of the third processing stage St3. Apart from these points, reference may be made to the fourth embodiment.

[0134] [Fig. 13] illustrates a first mode of operation of the fifth embodiment, making it possible to obtain an SRMS output signal suitable for reproduction by means of a monophonic sound system and including the out-of-phase content of the SSTer input stereo signal.

[0135] At a first processing stage, the stereophonic input signal SSTer is encoded into a so-called Mid / Side signal by means of a functional block MS-Enc. At this stage, the information contained in the stereophonic signal Sster is distributed into two channels designated by Mid and Side(L), as explained for the second mode of implementation.

[0136] The switching block Com5 is configured to transmit the Side(L) channel to the Ph-Shift functional block. The switching block Com6 is configured to transmit the Mid channel to the Sum2(L) functional block.

[0137] In the second processing stage, a phase shift function is applied to the Side(L) channel by means of the Ph-Shift functional block. In the present embodiment, a phase shift of +90° is applied to the Side(L) channel to obtain the Sh_Side(L) channel by means of the Ph+ phase shift functional block, configured to apply a phase shift to a signal provided as input and provide the phase-shifted signal as output.

[0138] In the third processing stage, an output channel L0Ut is generated so as to be suitable for transmission to a monophonic sound reproduction system, by means of a functional block MS-Dec, on the basis of the signals Mid and Sh_Side(L). This channel L0Ut forms the output signal Srms-

[0139] The output channel L0Ut is representative of the sum of the two channels Mid and Sh_Side(L) and can be calculated by applying to these channels a summation function by means of the functional block Sum2(L) configured to sum the signals supplied to it as input and provide their sum as output, such that LOut = Mid + Sh_Side(L). The signal SRMs of the present embodiment has the advantages and applications already mentioned for the signal Srms of the first and second embodiments.

[0140] [Fig. 14] illustrates a second mode of operation of the fifth implementation mode, allowing the out-of-phase signal to be specifically listened to. This second mode of operation is identical to the first mode of operation, except that the switching block Com6 is this time configured to block the transmission of the Mid channel to the functional block Sum2(L).

[0141] The result is at the output a signal S0P, corresponding to the signal Srms amputated from the cal Mid, that is to say having as content only the out-of-phase content of the original signal Sster- Thus, the listener can ensure the audible content of the out-of-phase signal and better perceive the advantage of the first mode of operation compared to a conventional monophonic signal, from which the out-of-phase content is absent. This mode of operation can be applied to all the modes of implementation previously described, by controlling the transmission and the blocking of the Mid channel(s) at the output of the first processing stage Stl.

[0142] [Fig. 15] illustrates a third mode of operation of the fifth mode of implementation, making it possible to obtain an SMono output signal suitable for reproduction by means of a monophonic sound system but not including the out-of-phase content of the original stereophonic signal, unlike the S rms signal of the first mode of operation.

[0143] Unlike the first and second operating modes, the Com5 switching block is configured to block transmission of the Side(L) channel to the Ph-Shift functional block. Furthermore, the Ph-Shift functional block can be disabled.

[0144] Consequently, the output channel LOut is only representative of the Mid channel, with L yes = Mid since only the Mid channel is provided as input to the Sum2(L) functional block. The SRMS signal of the present embodiment has the advantages and applications already mentioned for the Srms signal of the second embodiment.

[0145] The SMOno signal is formed from the single channel L0Ut, and can be supplied as input to a monophonic speaker. Since the out-of-phase content of the stereophonic signal SSTer is absent from the Mid channel, it is therefore also absent from the sound reproduction produced by the speaker, which therefore has a reduced information content compared to the original SSTer signal and the Srms signal.

[0146] Sixth mode of implementation

[0147] A sixth mode of implementation is illustrated by [Fig.16].

[0148] The first, second, third, fourth and fifth modes of implementation may be implemented in software, for example to apply a method according to the invention by means of a smartphone or other portable or non-portable sound reproduction device equipped with a monophonic speaker and supplied with stereophonic sound files. In this case, the transition from one operating mode to the other may be done manually according to the user's choice, by entering a command by means of a control interface, for example in the form of a dedicated physical button or a button forming part of a graphical interface of an application executing the method.

[0149] [Fig. 16] illustrates an example of a sound reproduction device with a Smart smartphone configured to implement the method according to the invention in software. The Smart smartphone comprises physical control buttons Btl, Bt2 and B3t, a computer calculation module Mod, a computer memory Mem in functional communication with the module Mem, and a speaker Spk. The Smart smartphone can use a graphical control interface Int displaying virtual buttons with the same respective functions as the physical buttons Btl, Bt2 and Bt3.

[0150] Thus, the smartphone Smart can include in computer form in its memory Mem instructions which, when executed by a computer calculation module Mod, lead the latter to apply to a stereophonic input signal S ster the steps of the method according to the invention, corresponding for example to one or the other of the first to fourth modes of implementation. The third mode of implementation represents an interesting compromise in the case of a smartphone in that it allows economical processing of smartphone resources while maintaining the possibility of stereophonic listening, which remains a possible option even with a smartphone.

[0151] The Btl button can be used to control the volume output by the speaker. Spk speaker.

[0152] The Bt2 button may be configured to enter the operating mode described by [Fig. 14], in which the Mid channel(s) is or are blocked at the output of the first processing stage, the other operations performed being such that the output signal produced includes the out-of-phase content of the original stereophonic signal without the Mid channel being present. The Bt2 button may be considered a Mid channel cutoff button in an operating mode intended for the generation of a monophonic signal including the out-of-phase content of an original stereophonic signal.

[0153] The button Bt3 can be configured to switch the device implementing the method from one of the operating modes to the other. If we consider for example the first mode of implementation, the first, second and third operating modes make it possible, from the same stereophonic signal SSTer, to generate (i) a monophonic signal Srms comprising out-of-phase content of the stereophonic signal, (ii) a monophonic signal Smono devoid of the out-of-phase content of the stereophonic signal, and (iii) to find a stereophonic signal Sstereo- Switching from one of these modes to the other allows the user to test which of these modes suits him best, and to listen to the difference between the reproduction of a monophonic signal containing the out-of-phase content (Srms) and that of a monophonic signal devoid of this out-of-phase content (Smono)- With the help of stereophonic headphones connected to the smartphone,the user can also compare the reproduction of these two signals with that of the corresponding stereophonic signal (S stereo) - Thus, the user can determine which operating mode of the method according to the invention suits him best, depending on his tastes and the piece being listened to.

[0154] The buttons Btl, Bt2 and Bt3 can be configured so that their respective actuations generate a signal or signals for controlling the software or hardware implementations of the phase shift, switching or selection functional groups, thus controlling the operating mode employed according to conventional methods. The physical buttons Btl, Bt2 and Bt3 could be respectively replaced by buttons Btl', Bt2' and Bt3' of a graphical interface.

[0155] Seventh mode of implementation

[0156] A seventh mode of implementation is illustrated by [Fig.14].

[0157] The first, second, third, fourth and fifth modes of implementation can be implemented in hardware by means of discrete components or by means of a so-called “DSP” (Digital Signal Processor in English terminology) chip integrated into a sound reproduction device, such as the monophonic speaker taken as an example in the present mode of implementation.

[0158] [Fig. 17] represents a monophonic speaker SpkMONo, such as a so-called "bluetooth" speaker, configured to implement the method according to the invention in hardware. The monophonic speaker SpkMono comprises the physical control buttons Bt1, Bt2 and Bt3 and a loudspeaker Spk like those mentioned in the sixth mode of implementation illustrated by [Fig. 16]. The button Bt3 can be configured to switch the device implementing the method from one of the operating modes to the other, thus allowing the user to choose the one that seems to best reproduce the piece of music being listened to, as already explained. The button Bt2 can allow the user to specifically listen to the out-of-phase content of the original stereophonic signal and thus allow him to be aware of its audio content.

[0159] The monophonic speaker SpkMono also comprises a DSP chip Chp configured to apply to an input stereophonic signal one or the other of the first to fourth implementation modes. The fourth and fifth implementation modes are particularly indicated: the monophonic speaker being by nature specialized in the sound reproduction of a monophonic signal, the operating modes intended to generate a stereophonic signal are superfluous. The fifth implementation mode (illustrated by figures 13 and 14) can be considered more economical due to its greater simplicity in comparison with the fourth implementation mode (illustrated by figures 11 and 12).

[0160] In the case where the SpkMONo speaker applies the fourth mode of implementation, the two-channel output signal (Srms or SMOno consisting of the two channels L0Ut and ROut) is transmitted to the Spk speaker via a module (not shown) merging the two channels in a conventional manner and possibly amplifying the resulting signal, then transmitting it to the Spk speaker.

[0161] In the case where the SpkMONo speaker applies the fifth implementation mode, the output signal (Srms or SMono consisting of the L0Ut channel) comprises only a single channel and does not require channel merging. It can therefore be directly transmitted to the Spk speaker, possibly via a module (not shown) amplifying the signal then transmitting it to the Spk speaker.

[0162] Eighth mode of implementation

[0163] An eighth mode of implementation is illustrated by [Fig. 18].

[0164] This mode of implementation applies to the broadcasting of music by a plurality monophonic speakers distributed in a space or a plurality of rooms, and is most often found in a building accessible to the public such as a shopping center or a nightclub, but also in private homes using so-called "multiroom" audio systems. In such situations, stereo listening phonic is impractical due to the nature of listening: loudspeakers must be distributed in different rooms or at different points in the same room without respecting the conditions necessary for stereophonic sound reproduction (in which the listener is equidistant from two loudspeakers directed towards him, and each diffusing one of a right channel and a left channel, respectively), the listener is also forced to move, thus moving away from certain loudspeakers in the system and closer to others.

[0165] Here, monophonic sound reproduction is the only practicable method, but, as already seen above, a conventional monophonic signal is devoid of the out-of-phase content of the original stereophonic signal. Applying the generation of a monophonic signal including the out-of-phase content of the original stereophonic signal makes it possible to significantly improve the sound quality of the broadcast music pieces.

[0166] [Fig. 18] illustrates such a music broadcasting system Sys, which comprises a centralization module Cent incorporating a control device Cont configured to receive and process an input stereophonic signal Sster so as to generate a monophonic signal SRMs comprising out-of-phase content of the stereophonic signal, according to any one of the embodiments described above, the third and fourth being particularly indicated for the reasons explained in relation to the seventh embodiment illustrated by [Fig. 17]. The system Sys also comprises a distribution module Dist, configured to receive the monophonic signal SRMS and distribute it in parallel by wired or wireless means, possibly in a modified or amplified form, to a plurality of monophonic speakers Spk.

[0167] The control device can use the DSP chip Chp configured to apply to the input stereophonic signal one or the other of the first to fourth implementation modes, and is configured to transmit the signal, Skms or SMOno, generated by the DSP chip Chp to the distribution module Dist. If necessary, the latter can be configured to merge the two channels of the signal supplied to it, before transmission to the monophonic speakers Spk.

[0168] Like the smartphone in [Fig.16] or the speaker in [Fig.17], the Sys system can be equipped with the Btl, Bt2 and Bt3 buttons, in physical or virtual form. As with the SMART smartphone and the SpkMONo speaker, the Bt2 button can be configured to allow the listener to switch to the mode for specifically listening to the out-of-phase content of the starting signal, separate from the Mid channel; the Bt3 button can be configured to switch between the operating modes of the implementation modes, with the associated advantages.

[0169] General considerations

[0170] In this description, an audio signal that does not contain information that makes it possible to produce a spatially defined spatial scene is considered to be monophonic. This will be the case for a signal that only contains one channel or a signal that has several channels with the same information content, for example two identical channels.

[0171] Also, in this description, the term “channel” designates a signal that can be considered in association with another channel. This is the case for a stereophonic signal composed of two channels.

[0172] Figures 9 to 14 illustrate situations in which signals are generated from an L^-R^ subtraction in which the right channel R1N is subtracted from the left channel L^, L1N and R1N representing respectively a left channel and a right channel of a stereophonic signal. This is an arbitrary choice used for explanatory purposes: an R1N-L1N subtraction could just as well be used.

[0173] The first, second, third and fourth embodiments may be implemented in an electronic device in software and managed, for example, by means of a dedicated software application. Alternatively, they may be implemented in an electronic device in hardware, by means of discrete electronic components or an electronic chip integrating all of the functions necessary for implementing the method.

[0174] The summing functional blocks mentioned in the present description are configured so as to sum the signals supplied to them as inputs. If two signals are supplied to these blocks, they output their sum. If only one signal is supplied, this signal is output unchanged at the output of the functional block.

[0175] The input stereophonic signal considered can be a digital signal or an analog signal, the implementation of the method of course being adapted to the nature of the signal.

[0176] In this document, the figures are not necessarily to scale. Some features and components may be shown exaggerated relative to other components or in a somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness.

[0177] Concerning an element of a figure defined within the framework of a given embodiment, reference may be made to the description concerning the characteristics and advantages of this same element in another embodiment. Similarly, unless otherwise indicated, it is possible to combine the described embodiments, as will be understood by those skilled in the art.

[0178] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention such as defined by the claims.

Claims

Claims

1. Method (100) for processing a stereophonic input signal (SSTer) comprising a left channel (L^) and a right channel (R1N), comprising the steps of: - generating a center channel (Mid) and a first side channel (Side(L), Side(R)), the center channel being representative of a sum of the left channel (L1N) and the right channel (R1N) and the first side channel (Side(L), Side(R)) being representative of a subtraction of one of the left channel (L1n) and the right channel (R^) from the other of the left channel (L1N) and the right channel (R^); - phase shifting the first side channel (Side(L)) by 90° in a first direction to obtain a first phase-shifted side channel (Sh_Side(L)); and - generate a first monophonic output channel (Srms) representative of a sum of the central channel (Mid) and the first phase-shifted side channel (Sh_Side(L)).

2. The processing method according to claim 1, further comprising the steps of: - generating a second side channel (Sh_Side(R)) of opposite polarity to the first side channel (Sh_Side(L)); - phase shifting by 90° in a second direction opposite to the first direction the second side channel (Sh_Side(R)) to obtain a second phase-shifted side channel (Sh_Side(R)); - generating a second monophonic output signal (ROut) representative of a sum of the central channel (Mid) and the second phase-shifted side channel (Sh_Side(R)), wherein the first monophasic output channel (LOut) and the second monophonic output channel (Roui) form a two-channel monophonic output signal (Srms).

3. The processing method according to claim 1, wherein the first side channel (Side(L)) is representative of a subtraction in which the right channel (Rin) is subtracted from the left channel (L1N), and the first side channel (Side(L)) is phase shifted by +90°.

4. Computer program comprising instructions which, when the program is executed by a digital computer, cause the latter to apply to a stereophonic input signal (SSTer) the steps of the method according to any one of claims 1 to 3.

5. A computer-readable medium comprising instructions which, when executed by a digital computer, cause the latter to apply to a stereophonic input signal (SSTer) the steps of the method according to any one of claims 1 to 3.

6. Electronic chip (Chp) configured to implement the steps of the method according to any one of claims 1 to 3.

7. Electronic device (SMART, SpkMONo, Sys, Cent) configured to implement the steps of the method according to any one of claims 1 to 3 by software or by hardware.

8. The device of claim 7, configured to transition from a first mode of operation in which the device generates the first monophonic output channel (SRMS) to a second mode of operation in which the device generates a monophonic output channel representative of the center channel (SMONo)-

9. The device of claim 8, wherein out-of-phase content of the stereophonic input signal (Sster) is absent from the monophonic output channel representative of the center channel (Mid).

10. The device according to claim 8 or 9, comprising a control interface (Bt3, Bt3') configured to switch the device from the first operating mode to the second operating mode.

11. The device according to any one of claims 7 to 10, comprising a control interface (Bt2, Bt2') configured to switch the device from the first operating mode to an operating mode in which the first monophonic output channel (S Op) is representative of the first phase-shifted side channel (Sh_Side(L)) excluding the center channel (Mid).

12. The device according to any one of claims 7 to 11, chosen from a smartphone (SMART), a monophonic speaker (SpkMONo), a system (Sys) for broadcasting sound recordings, and a centralization module (Cent) configured to distribute the first monophonic output channel (L0Ut) to a plurality of speakers.

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