Sound acquisition method and system, and sound acquisition and reproduction apparatus

Claim 2

A sound acquisition system comprising a number n greater than 2 of sound receiving devices (M1 to M4; 100; 300; 400) arranged, at regular intervals, over a circumference (13) centered with respect to a direction of symmetry (D), and processing means (8) for processing the signals generated from said sound receiving devices, characterized in that the sound receiving devices comprise microphones (M1, M2, M3, M4; 100; 301; 400) arranged in a same plane (P) perpendicular to said direction of symmetry (D), each microphone being arranged in one of a plurality of cavities (12; 112) open on one side (23) facing a planar plate (20; 510) reflecting sound waves and disposed in parallel to said plane (P) in which said sound receiving devices are arranged.

Claim 3

A sound acquisition and reproduction apparatus according to claim 1, wherein said processing means (8) comprise means for applying a phase shift equal to 360° divided by n between the signals output respectively by any two adjacent sound reception devices, and for adding the signals thus phase shifted in such a way as to obtain a substantially uniform and non-attenuated reception of signals relating to the components parallel to the plane (P) irrespective of the direction of the waves and substantially zero reception of the signals relating to the components parallel to the straight line of symmetry (D) of the acoustic waves picked up.

Claim 4

The system as claimed in claim 2, wherein said sound reception devices (M1 to M4; 100; 300) are even in number, m=2n greater than 3, and are associated two by two, in n pairs, the sound reception devices of each of said pairs being arranged symmetrically with respect to the direction of symmetry (D), the processing means (8) being configured so that the signals output respectively by the reception devices of each pair are subtracted from one another in order to add them with a phase shift of 180° between them, a phase shift being applied to each signal (S13, S14) output by a pair in order to obtain a phase shift of 360°/m between the signals output respectively by any two adjacent pairs of sound reception devices, the signals thus phase shifted then being added.

Claim 5

The system as claimed in claim 3, wherein the processing means (8), for each pair of sound reception devices (M1 to M4; 100; 300; 400) comprise a differential preamplifier (A13 and A24) including two inputs (E1, E3 and E2, E4) respectively receiving the signals output by the two sound reception devices (M1 to M4; 100, 300) of the pair, and an output supplying the amplified difference (S13 and S24) between the two signals received at the inputs (E1 to E4).

Claim 7

The system as claimed in claim 5, wherein each phase-shifter channel (D13, D24) comprises an association, in series, of several all-pass cells (PT1A, PT2B, PT1C; PT2A, PT1B, PT2C) belonging to two types of all-pass cells (PT1, PT2), wherein a first type of all-pass cell (PT1) comprises a resistor (R 1 ) and a capacitor (C 1 ), the values of which determine the dependency of an elementary phase shift supplied by the all-pass cell (PT1) between its output signal and its input signal as a function of the frequency of its input signal, this elementary phase shift lying between 0° and 180° and being substantially equal to 90° for a reference frequency f 1 =1/(2πR 1 C 1 ) of the all-pass cell (PT1), wherein a second type of all-pass cell (PT2) comprises a resistor (R 2 ) and a capacitor (C 2 ) the values of which determine the dependency of an elementary phase shift supplied by the all-pass cell (PT2) between its output signal and its input signal as a function of the frequency of its input signal, this elementary phase shift lying between 180° and 360° and being substantially equal to 270° for a reference frequency f 2 =1/(2πR 2 C 2 ) of the all-pass cell (PT2), and wherein the all-pass cells associated in series in each phase-shifter channel (D13, D24) comprise at least one set of all-pass cells (PT1A, PT2B, PT1C; PT2A, PT1B, PT2C) which, considered in the increasing order of their reference frequencies, are alternatively of the first (PT1) and of the second (PT2) type and have reference frequencies (F, KF, K 2 F; G, KG, K 2 G) substantially in geometric progression according to a ratio (K) which is identical for both phase-shifter channels (D13, D24).

Claim 8

The system as claimed in claim 6, wherein the ratio (K) of the geometric progressions is approximately equal to e.sup.π.

Claim 12

The system as claimed in claim 10, wherein each sound reception device (300) consists of several microphones (301), and wherein the processing means (8) comprise means for adding the signals, in phase, output respectively by the microphones (301) constituting each sound reception device (300) in order to establish the output signal of this sound reception device (300).

Claim 13

A sound acquisition and reproduction apparatus according to claim 11, wherein a frequency band of said output signal can be extended to include telephony frequency bands by reducing the dimensions of the microphone mounting assembly.

Claim 14

The system as claimed in claim 1, wherein the cavities (12; 112) in which the said microphones (M1 to M4; 100; 301; 400) are housed are formed in a body (2; 102; 202; 302; 402; 502) of symmetric shape with respect to said direction of symmetry (D) and including, on the same side as said planar plate (20; 510) reflecting the sound waves, an elongation (21; 121; 221) for defining a defined spacing d (22) between the cavities (12; 112) and said plate (20; 510).

Claim 17

A sound acquisition and reproduction apparatus, wherein said sound reproduction means comprises at least one loudspeaker (4; 504, 505), and wherein said sound acquisition means comprises a number n greater than 2 of sound receiving devices (M1 to M4; 100; 300; 400) and arranged, at regular intervals, over a circumference (13) centered with respect to a direction of symmetry (D), and processing means (8) for processing the signals generated from said sound receiving devices, characterized in that the sound receiving devices comprise microphones (M1, M2, M3, M4; 100; 301; 400) arranged in a same plane (P) perpendicular to said direction of symmetry (D), each microphone being arranged in one of a plurality of cavities (12; 112) open on one side (23) facing a planar plate (20; 510) reflecting sound waves and disposed in parallel to said plane (P) in which said sound receiving devices are arranged, said sound reproduction means being arranged on the axis of symmetry (D) in such a way that said sound acquisition and reproduction apparatus exhibits a generally symmetric structure about said direction of symmetry (D).

Claim 18

A sound acquisition and reproduction apparatus, wherein said sound reproduction means comprises at least one loudspeaker (4; 504, 505), and wherein said sound acquisition means comprises a number n greater than 2 of sound receiving devices (M1 to M4; 100; 300; 400) and arranged, at regular intervals, over a circumference (13) centered with respect to a direction of symmetry (D), and processing means (8) for processing the signals generated from said sound receiving devices, characterized in that the sound receiving devices comprise microphones (M1, M2, M3, M4; 100; 301; 400) arranged in a same plane (P) perpendicular to said direction of symmetry (D), each microphone being arranged in one of a plurality of cavities (12; 112) open on one side (23) facing a planar plate (20; 510) reflecting sound waves and disposed in parallel to said plane (P) in which said sound receiving devices are arranged, said sound reproduction means being arranged on the axis of symmetry (D) in such a way that said sound acquisition and reproduction apparatus exhibits a generally symmetric structure about said direction of symmetry (D).