Adjustable soundstage sound reproduction equipment

Abstract

Adjustable Soundstage Reproduction Equipment The equipment (10) comprises: - a speaker (20) with: - a center speaker (28A, 28B); - two side speakers (24, 26); - an information processing unit (30, 56, 60) to form: - a center channel; - a center signal for the center speaker; and - a right, or left, signal applied to the right, or left, speaker. The unit is suitable for forming the signals: - in stereo mode: - the center signal is the center channel; - the right, or left, signal is the right channel minus the center channel; and - in omnidirectional mono mode: - the speaker signals are a combination of the right and left channels; - in unidirectional mono mode: - one of the signals is a combination of the right and left channels, and the other signals are zero. Figure for the abbreviation: 1

Description

Title of the invention: Sound reproduction equipment with adjustable sound stage

[0001] The present invention relates to sound reproduction equipment, of the type comprising:

[0002] - an input for a stereophonic signal with a right channel and a left channel;

[0003] - an enclosure with:

[0004] - at least one central loudspeaker oriented to diffuse in one direction main;

[0005] - two right and left side speakers oriented to diffuse in different directions opposite in a direction defining an angle between 70 and 110° relative to the main direction,

[0006] - an information processing unit for combining the right and left channels left to form:

[0007] - a central channel formed from a combination of the left and right channels;

[0008] - at least one central excitation signal applied to the or each loudspeaker central;

[0009] - a right excitation signal applied to the right loudspeaker; and

[0010] - a left excitation signal applied to the left speaker.

[0011] Current usage favors listening to music from a single speaker. There are "mono" speakers and "stereo" speakers.

[0012] “Stereo” speakers have two loudspeakers reproducing the right and left channels separately.

[0013] "Mono" speakers reproduce a single sound formed by the combination of the right and left channels of the recording. They include unidirectional speakers in which the sound is diffused in a single direction and omnidirectional speakers in which the sound is diffused in several directions.

[0014] Each type of speaker has its own advantages. Depending on the desired use, and in particular the type of content reproduced, the listening level, the acoustic environment, the position and the number of listeners, it is preferable to use a stereo speaker, a unidirectional mono speaker or an omnidirectional mono speaker.

[0015] The possession of the three types of speaker leads to high expenses which a good number of users forgo, thus limiting, depending on the conditions, the quality of the sound reproduction.

[0016] The aim of the invention is to propose sound reproduction equipment at a cost reduced to provide satisfactory restitution quality, whatever the conditions of use.

[0017] To this end, the invention relates to sound reproduction equipment of the aforementioned type, characterized in that the information processing unit is capable of forming the excitation signals according to 3 distinct diffusion modes according to which:

[0018] - in stereo mode:

[0019] - for at least some frequencies, the or each central excitation signal is the central channel;

[0020] - for at least some frequencies, the right excitation signal is the right channel decreased central canal; and

[0021] - for at least some frequencies, the left excitation signal is the channel left decreased from the central signal;

[0022] - in an omnidirectional mono mode:

[0023] - the excitation signals of all the loudspeakers are the same mono combination right and left channels;

[0024] - in a unidirectional mono mode:

[0025] - for at least some frequencies, only one of the excitation signals is a mono combination of the right and left channels and other speaker excitation signals are harmed; and

[0026] in that it comprises a member for selecting at least one diffusion mode.

[0027] Depending on the particular embodiments, the equipment comprises one or more of the following characteristics:

[0028] - the central channel is a correlation of the right and left channels;

[0029] - in unidirectional mono mode, for frequencies lower than one frequency reference, the excitation signals of all loudspeakers are the same mono combination of the right and left channels;

[0030] - in unidirectional mono and omnidirectional mono modes, the combination mono of right and left channels is the sum of right and left channels;

[0031] - the selection member is capable of allowing the selection of a combination of broadcasting modes, and in that the information processing unit is capable of forming each excitation signal as a combination of the corresponding excitation signals defined in each broadcasting mode as a function of the state of the selection member;

[0032] - the information processing unit comprises a weighting module specific to providing a weighting of the different diffusion modes according to the state of the selection member and a distributor capable of forming each excitation signal as a combination of the corresponding excitation signals defined in each diffusion mode according to the weighting provided by the weighting module;

[0033] - the information processing unit comprises a distributor in which is stored, for each diffusion mode, at least one transfer matrix and in that the distributor is capable, for each diffusion mode, of forming the excitation signals as the product of the associated transfer matrix by a vector comprising the central channel, the right channel reduced by the central channel, the right channel reduced by the central signal, and the mono combination of the right and left channels.

[0034] The invention will be better understood upon rereading the description which follows, given solely by way of example and with reference to the drawings in which:

[0035] - [Fig.l] [Fig.l] is a schematic view of sound reproduction equipment according to the invention.

[0036] The sound reproduction equipment 10 illustrated in [Fig.l] is adapted to be connected to a source 12 of stereophonic signals through a right input 14 for a right channel denoted R and a left input 16 for a left channel denoted L.

[0037] The sound reproduction equipment comprises an enclosure 20 delimiting a box in which several loudspeakers are arranged immobilized in position relative to each other.

[0038] The enclosure comprises two right 24 and left 26 lateral loudspeakers arranged to emit in opposite directions. Their axes are angularly offset by an angle less than or equal to twenty degrees and are advantageously coaxial but opposite.

[0039] Alternatively, the loudspeakers 24 and 26 are replaced by groups of right and left side loudspeakers each per group, each group being supplied by the same loudspeaker signal.

[0040] The enclosure further comprises a front central loudspeaker 28A and a rear central loudspeaker 28B whose emission axes are arranged substantially along the bisector of the angle delimited by the emission axes of the side loudspeakers 24 and 26.

[0041] The two central loudspeakers 28A and 28B are arranged with their emission directions opposite.

[0042] The sound reproduction equipment comprises a conditioner 30 formed of an information processing unit suitable for carrying out the processing described below. The information processing unit comprises an extraction stage 36 suitable for producing, from the right R and left L channels received from the inputs 14 and 16, a central conditioned channel C formed of the information common to the right R and left L channels.

[0043] The extraction stage 36 is capable of providing a correlation function for the right R and left L channels. Alternatively, the stage 36 implements an algorithm for calculating the central channel C in the frequency domain as described in the article Frequency-Domain Two-to Three-Channel Upmix for Center Channel Derivation and Speech Enhancement, Earl Vickers1, 'STMicroelectronics, Santa Clara, CA 95054, earl. vickers @ st.com.

[0044] It further comprises two own subtractors 44, 46 connected respectively to input 14 to receive the right channel R and to input 16 for the left channel L. On their other inputs, the subtractors 44, 46 receive the same central channel C so that each subtractor 44, 46 respectively ensures the difference between the right channel R respectively left L and the central channel C. At the output of these subtractors, two right and left decohered channels are obtained, denoted R' = R - C and L' = L - C.

[0045] The conditioner 30 further comprises a summer 47 whose inputs are connected to the two inputs 14 and 16. This summer is capable of producing at output a mono combination of the right R and left L channels called mono channel, noted M, and formed from the sum of the right R and left L channels so that M = L + R.

[0046] The equipment 10 further comprises a selection member 50 allowing the user to select three distinct broadcasting modes ensuring unidirectional mono or mono monodirectional or stereophonic broadcasting and a combination of these two by two.

[0047] This selection member 50 is for example a rotary selection member. It comprises a cursor that can be rotated through 360 degrees relative to a fixed part of the selection member. Depending on the position of the cursor, the selection member is capable of producing, at output, an angle 0 representative of the position of the rotary cursor. The angle 0 then takes all the values ​​between 0 and 360° depending on the position of the cursor or between 0 and 2ir if the values ​​of the angle 0 are expressed in radians. The values ​​of 0 are expressed modulo 360° or 2ir depending on the case to take into account the infinite rotation of the cursor.

[0048] On the fixed part of the selection member, around the axis of rotation of the cursor, three indexes are arranged angularly spaced by 120 degrees, an index 54A designating the omnidirectional mono mode, an index 54B designating the unidirectional mono mode and an index 54C designating the stereophonic mode.

[0049] The selection member 50 is connected to a weighting module 56 receiving as input the angle 0 representative of the position of the cursor 52. This weighting module is capable of generating three weighting coefficients a, [3, y, each between 0 and 1. They are representative of the weighting of each of the modes chosen by the user as a function of the position of the cursor 52.

[0050] The coefficient a is associated with the omnidirectional mono mode, the coefficients [3 and y being associated with the unidirectional mono and stereophonic modes respectively.

[0051] The weighting module 56 is capable of assigning, to a given coefficient, the maximum value 1 when the cursor is on the index of the mode associated with this coefficient and of making the coefficient smaller the further the cursor moves away, in one direction or the other, from the index of the mode associated with the coefficient considered. The coefficient is zero when the cursor is on the other two indexes corresponding to the other two modes or between these two indexes.

[0052] For example, each of the coefficients a, [3, y follows a trigonometric law as indicated below.

[0053] if 0 e [ ™ ), a = cos(^0)

[0054] if0e [^L±l],a = 0

[0055] 810^^^),0 = ^5(2(0-^))

[0056] si0e[^I;o],P = O

[0057] 810^^^),7 = 005(1(04--))

[0058] if0e [0;Ÿ]'Y = 0

[0059] The weighting module 56 is connected to a distributor 60 capable of receiving the three weighting coefficients a, [3 and y.

[0060] The distributor 60 has four inputs for the conditioned channels, namely the right R' and left L' decorrelated channels, the central channel C and the mono channel M from the conditioner 30.

[0061] The distributor has four outputs for excitation signals from the four loudspeakers and in particular right SR and left SL excitation signals for the right and left loudspeakers 24 and 26 respectively, a front central excitation signal denoted SCF for the front loudspeaker 28A and a rear central excitation signal SCb for the rear central loudspeaker 28B.

[0062] The sound reproduction equipment finally comprises four amplifiers 64, 66, 68 and 70 for the loudspeaker signals SR, SL, SCf and SCb-

[0063] The outputs of amplifiers 64 and 66 are connected to the side loudspeakers or groups of loudspeakers 24 and 26 while the outputs of amplifiers 68 and 70 are connected to the front center loudspeaker or group of loudspeakers 28A and rear 28B respectively.

[0064] The distributor 60 is capable of defining each of the excitation signals as a linear combination of the conditioned channels. The linear application giving the excitation signals of the loudspeakers as a function of the conditioned channels S is defined by the matrix MM formed from the sum of three distribution matrices M1, M2 and M3 each specific to a diffusion mode, each matrix being weighted by the coefficient a, [3, y specific to the mode from the weighting module 56.

[0065] More precisely, a first matrix Ml characteristic of the omnidirectional mono mode is stored in the distributor. This matrix Ml is reproduced below multiplied by its associated coefficient a. The excitation signals obtained are indicated as a function of the conditioned channels received by application of the matrix ML

[0066] / 0

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077] i\ ii L L '\c \mid $CF ' Scb / The matrix Ml is such that in the omnidirectional mono mode with the cursor on index 54A for all frequencies, the excitation signals SL, SCp, SR and SCb are each equal to the mono channel M. Two matrices M2a and M2b specific to the unidirectional mono mode are stored in the distributor 60. The matrix M2a is used for the combination of the conditioned channels for frequencies lower than a reference frequency fref while the matrix M2b is implemented for signals of frequencies higher than this reference frequency fref. The matrices M2a and M2b are expressed as shown below under the same conditions as the matrix ML. Note that the matrices M1 and M2a are identical. For M2a: / 0 0 0 For M2b: / 0 0 0 V \MI SCF Sr \Scb / 01 'L'\C R \MID SCF Sr Thus, these matrices are such that in the unidirectional mono mode with the cursor on index 54B, the excitation signals SL, SCh Sr and SCb are each equal to the mono channel M for frequencies lower than fref. For frequencies above fref, all excitation signals are muted except for the central excitation signal before SCf which is equal to the mono channel M. Finally, for pure stereophonic mode, the crossover 60 applies a matrix M3 stored in the crossover whatever the frequency. This matrix M3 is shown below under the same conditions as the matrix ML Y'o 10 01 jL'\ 0 C 0 ! R 0 / \MI °CF Sr PCB /

[0078] This matrix is ​​such that, in the pure stereophonic mode with the cursor on the index 54C, for all the right SR and left SL excitation signals are respectively equal to the right R' and left L' decorrelated channels, the front SCf and rear SCb central excitation signals both being equal to the central channel C.

[0079] For any position of the selection member 50, the distributor 60 is thus able to define the excitation signals SL, SCf, Sr and SCB of the loudspeakers as a linear function whose matrix MM is given by MM = aMi + [3M2 + yM3 where M2 is equal to M2a or M2b depending on the frequency.

[0080] The coefficients a, [3 and y come from the weighting module 56.

[0081] It is understood that the selection member 50 allows the user to gradually vary the spatial behavior of the speaker between three particular modes, namely stereo mode, unidirectional mono mode and omnidirectional mono mode, depending on its use, while maintaining a frequency response and an objective rendering of the timbres that is consistent between all the modes.

[0082] When the cursor is between two indexes, the two modes associated with these indexes are combined with a weighting fixed by the coefficients defined by the weighting module.

[0083] Alternatively, the central conditioned channel C is formed not from the correlation of the L and R channels but from the sum of the L and R channels. The central channel C is then obtained at the output of the adder 47, the extraction stage 36 being eliminated. More generally, the central conditioned channel C is formed from a combination of the L and R channels.

[0084] According to yet another variant, the same passage matrix M2 = M2b is used regardless of the frequency of the signal for the unidirectional mono mode and the matrix M2a does not exist.

[0085] Alternatively, in each of the modes, several passage matrices are defined according to the frequency ranges of the signal, for example what is presented for the unidirectional mono mode.

[0086] In particular, for example, in the stereophonic mode, the matrix M3 is used for frequencies higher than a reference frequency and the matrix M2a is used for frequencies lower than this reference frequency.

[0087] Alternatively, a single center speaker is used. Thus, the rear center speaker 28B is removed along with its control chain and only the front center speaker 28A is retained.

[0088] According to an alternative embodiment, the selection member is not continuously variable between the three modes but a discrete selection member, with 3 positions, one per mode or with 6, 9, 12, etc. positions for linear combinations of modes.

[0089] In all cases, the selection member is in a variant with rectilinear and non-rotating movement. In a variant, it is formed of a cursor movable on a screen and whose position is representative of the value 0.

Claims

Demands

1. Sound reproduction equipment (10) comprising: - an input (14, 16) for a stereophonic signal with a right channel (R) and a left channel (L); - a speaker (20) with: - at least one center loudspeaker (28A, 28B) oriented to radiate sound in a main direction; - two right (24) and left (26) side loudspeakers oriented to radiate sound in directions defining an angle between 70 and 110° with respect to the main direction, - an information processing unit (30, 56, 60) for combining the right (R) and left (L) channels to form: - a center channel (C) formed from a combination of the left (R) and right (L) channels; - at least one center excitation signal (SCf, SCb) applied to the center loudspeaker(s) (28A, 28B); - a right excitation signal (SR) applied to the right speaker (24);and - a left excitation signal (SL) applied to the left loudspeaker (26), characterized in that the information processing unit (30, 56, 60) is suitable for forming the excitation signals (SR, SL, SCh, SCb) according to 3 distinct diffusion modes according to which: - in a stereo mode: - for at least certain frequencies, the center excitation signal(s) (SCf, SCb) is the center channel (C); - for at least certain frequencies, the right excitation signal (SR) is the right channel (R) minus the center channel (C); and - for at least certain frequencies, the left excitation signal (SL) is the left channel (L) minus the center signal (C); - in a mono omnidirectional mode: - the excitation signals (SR, SL, SCp, SCb) of all loudspeakers (24, 26, 28A, 28B) are the same mono combination of the right (R) and left (L) channels;- in a unidirectional mono mode: - for at least some frequencies, only one of the excitation signals (SR, SL, SCf, SCb) is a mono combination of the channels; right (R) and left (L) and the other excitation signals (SR, SL, SCh Scb) of the loudspeakers (24, 26, 28A, 28B) are degraded; and in that it comprises a selection element (50) of at least one diffusion mode. - the selection element (50) being suitable for allowing the selection of a combination of diffusion modes, and the information processing unit (30, 56, 60) being suitable for forming each excitation signal (SR, SL, SCF, SCB) as a combination of the corresponding excitation signals defined in each diffusion mode according to the state of the selection element (50).

2. Equipment according to claim 1, characterized in that the central channel (C) is a correlation of the right (R) and left (L) channels.

3. Equipment according to claim 1 or 2, characterized in that in the unidirectional mono mode, for frequencies below a reference frequency, the excitation signals (SRi, SLb SCf, Scb) of all loudspeakers (24, 26, 28A, 28B) are the same mono combination of the right (R) and left (L) channels.

4. Equipment according to any one of the preceding claims, characterized in that in mono unidirectional and mono omnidirectional modes, the mono combination of the right (R) and left (L) channels is the sum of the right (R) and left (L) channels.

5. Equipment according to any one of the preceding claims, characterized in that the information processing unit (30, 56, 60) comprises a weighting module (56) suitable for providing a weighting (a, [3, y) of the different diffusion modes as a function of the state of the selection member (50) and a distributor (60) suitable for forming each excitation signal (SR, SL, SCh SCb) as a combination of the corresponding excitation signals defined in each diffusion mode as a function of the weighting (a, [3, y) provided by the weighting module (56).

6. Equipment according to any one of the preceding claims, characterized in that the information processing unit (30, 56, 60) comprises a distributor (60) in which at least one transfer matrix (M1, M2a, M2b, M3) is stored for each diffusion mode, and in that the distributor (60) is suitable, for each diffusion mode, for forming the excitation signals (SR, SL, Scf, Scb) as the product of the associated transfer matrix and a vector including the center channel (C), the right channel (R) minus the center channel (C), the right channel (R) minus the center signal (C), and the mono combination of the right (R) and left (L) channels.

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