Multidirectional sound reproduction

Claim 2

A signal-processing apparatus for use in the production or reproduction of multidirectional audio signals comprising matrixing means for producing a set of output signals from a set of input signals, each signal of at least one of said sets being identified with a different sound-direction bearing angle, means for mixing the input signals with mixing coefficients defined for each respective value of a 360* repetitive single-variable function of bearing angle for each output signal to provide the respective output signals, said single-variable functions having the characteristic that when each output signal is multiplied by the complex conjugate of the respective function of another bearing angle and all such products are added, the sum produced thereby is a sum of input signals each multiplied by a coefficient that is a function solely of the difference between both bearing angles.

Claim 5

In a method of reproducing directional audio information from a plurality of source signals to form a plurality of presentation signals, wherein the source signals are representative of sounds from different bearing angles theta , eaCh measured from a source reference direction, and are matrixed to form transmission signals having encoding mixing coefficients, at least one of said transmission signals having encoding mixing coefficients substantially corresponding to values of a given single-variable function of the bearing angle theta of the respective sounds, the steps of re-matrixing the transmission signals to form signals for presentation at bearing angles phi , each measured from a presentation reference direction having a specific angular relation to said source reference direction, by multiplying each transmission signal by a decoding mixing coefficient substantially corresponding to the value of a single-variable function of phi for each presentation bearing angle, said function of phi being the complex conjugate of the function of theta defining the encoding mixing coefficients for each transmission signal, and adding the resultant product signals to form each presentation signal, so that the sum of all product signals of the function of theta applied to the source signals in formation of each transmission signal with the function of phi applied to that transmission signal in the formation of each presentation signal is a 360* repetitive single-variable function of the difference between the angles theta and phi having a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle, and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 6

In a method of reproducing directional audio information from a plurality of source signals to form a plurality of presentation signals, wherein the source signals are representative of sounds from different bearing angles theta , eaCh measured from a source reference direction, and are matrixed to form transmission signals having encoding mixing coefficients, at least one of said transmission signals having encoding mixing coefficients substantially corresponding to values of a given single-variable function of the bearing angle theta of the respective sounds, the steps of re-matrixing the transmission signals to form signals for presentation at bearing angles phi , each measured from a presentation reference direction having a specific angular relation to said source reference direction, by multiplying each transmission signal by a decoding mixing coefficient substantially corresponding to the value of a single-variable function of phi for each presentation bearing angle, said function of phi being the complex conjugate of the function of theta defining the encoding mixing coefficients for each transmission signal, and adding the resultant product signals to form each presentation signal, so that the sum of all product signals of the function of theta applied to the source signals in formation of each transmission signal with the function of phi applied to that transmission signal in the formation of each presentation signal is a 360* repetitive single-variable function of the difference between the angles theta and phi having a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle, and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 7

In a method of producing signals with directional audio information from a plurality of source signals which includes matrixing of said source signals representative of sounds from different bearing angles theta to form transmission signals capable of bein re-matrixed for production of a plurality of presentation signals at bearing angles phi , the bearing angles theta being measured from a source reference direction and the bearing angles phi being measured from a presentation reference direction having a specific angular relation to said source reference direction, said method comprising the steps of mixing the source signals with mixing coefficients defined for each respective value of a given 360* repetitive single-variable function of the bearing angles theta for each transmission signal to provide said transmission signals, the respective single-variable functions having the characteristic that when each transmission signal is multiplied by the complex conjugate of the respective function of the bearing angle phi and all such products are added, the sum produced thereby is a sum of input signals each multiplied by a coefficient that is a function solely of the difference between said bearing angles theta and phi , and has a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle and absolute values at intermediate angles symmetrical with the respect to the axis thus defined.

Claim 8

In a method of producing signals with directional audio information from a plurality of source signals which includes matrixing of said source signals representative of sounds from different bearing angles theta to form transmission signals capable of bein re-matrixed for production of a plurality of presentation signals at bearing angles phi , the bearing angles theta being measured from a source reference direction and the bearing angles phi being measured from a presentation reference direction having a specific angular relation to said source reference direction, said method comprising the steps of mixing the source signals with mixing coefficients defined for each respective value of a given 360* repetitive single-variable function of the bearing angles theta for each transmission signal to provide said transmission signals, the respective single-variable functions having the characteristic that when each transmission signal is multiplied by the complex conjugate of the respective function of the bearing angle phi and all such products are added, the sum produced thereby is a sum of input signals each multiplied by a coefficient that is a function solely of the difference between said bearing angles theta and phi , and has a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle and absolute values at intermediate angles symmetrical with the respect to the axis thus defined.

Claim 9

An audio recording having transmission signals formed from the matrixing of a plurality of source signals representative of sounds from different bearing angles theta and capable of being re-matrixed for production of a plurality of presentation signals at bearing angles phi , the bearing angles theta being measured from a source reference direction and the bearing angles phi being measured from a presentation refererence direction having a specific angular relation to said source reference direction, at least one of said transmission signals including the sum of mixed signals each formed by mixing the source signals with mixing coefficients defined for each respective value of a given 360* repetitive single-variable function of the bearing angles theta for each transmission signal, and said given single-variable function has the characteristic that when it is multiplied by the complex conjugate of said function oF the bearing angle phi and all such product functions are added, the sum produced thereby is a function solely of the difference between said bearing angles theta and phi , and has a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 10

An audio recording having transmission signals formed from the matrixing of a plurality of source signals representative of sounds from different bearing angles theta and capable of being re-matrixed for production of a plurality of presentation signals at bearing angles phi , the bearing angles theta being measured from a source reference direction and the bearing angles phi being measured from a presentation refererence direction having a specific angular relation to said source reference direction, at least one of said transmission signals including the sum of mixed signals each formed by mixing the source signals with mixing coefficients defined for each respective value of a given 360* repetitive single-variable function of the bearing angles theta for each transmission signal, and said given single-variable function has the characteristic that when it is multiplied by the complex conjugate of said function oF the bearing angle phi and all such product functions are added, the sum produced thereby is a function solely of the difference between said bearing angles theta and phi , and has a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 11

In the method of reproducing directional audio information which includes producing source signals corresponding to sound emanating from locations at bearing angles differing in side-to-side and front-to-back orientation with respect to a listener, the steps of encoding and mixing the source signals in accordance with first sets of predetermined amplitude and phase coefficients said first sets of coefficients being defined by 360* repetitive functions of said source bearing angles to produce a number of transmission signals smaller than the number of source signals, there being a respective function for each transmission signal, and decoding and separating the transmission signals in accordance with second sets of predetermined amplitude and phase coefficients said second sets of coefficients being defined by complex conjugates of said respective functions of a presentation bearing angle to produce presentation signals corresponding to angular positions of greater number than the number of transmission signals, each presentation signal comprising a plurality of source signals mixed in accordance with third sets of amplitude and phase coefficients constituting sums of products of said first and second sets, the coefficients of the third sets representing the proportion with which each source signal component is represented in each presentation signal, said coefficients of said third set being defined by functions of the bearing angles between the source direction and the presentation direction and all of said functions being identical for all such third set coefficients, whereby the presentation signals are directionally symmetrical.

Claim 12

In the method of reproducing directional audio information which includes producing source signals corresponding to sound emanating from locations at bearing angles differing in side-to-side and front-to-back orientation with respect to a listener, the steps of encoding and mixing the source signals in accordance with first sets of predetermined amplitude and phase coefficients said first sets of coefficients being defined by 360* repetitive functions of said source bearing angles to produce a number of transmission signals smaller than the number of source signals, there being a respective function for each transmission signal, and decoding and separating the transmission signals in accordance with second sets of predetermined amplitude and phase coefficients said second sets of coefficients being defined by complex conjugates of said respective functions of a presentation bearing angle to produce presentation signals corresponding to angular positions of greater number than the number of transmission signals, each presentation signal comprising a plurality of source signals mixed in accordance with third sets of amplitude and phase coefficients constituting sums of products of said first and second sets, the coefficients of the third sets representing the proportion with which each source signal component is represented in each presentation signal, said coefficients of said third set being defined by functions of the bearing angles between the source direction and the presentation direction and all of said functions being identical for all such third set coefficients, whereby the presentation signals are directionally symmetrical.

Claim 13

A signal-processing system for producing or reproducing directional audio information comprising encoding means for matrixing source signals representative of sounds from different bearing angles theta , each measured from a source reference direction, to form transmission signals having encoding mixing coefficients, at least one of said signals having encoding mixing coefficients substantially corresponding to values of a given single-variable function of the bearing angle theta of the respective sounds, decoding means for re-matrixing the transmission signals to form signals for presentation at bearing angles phi , each measured from a presentation reference direction having a specific angular relation to said source reference direction, said decoding means having means for multiplying each transmission signal by a decoding mixing coefficient substantially corresponding to the value of a single-variable function of phi for each presentation bearing angle, said function of phi being the complex conjugate of the function of theta defining the encoding mixing coefficients for each transmission signal, and means for adding the resultant product signals to form each presentation signal, so that the sum of all products of the function of theta applied to the source signals in formation of each transmission signal with the function of phi applied to that transmission signal in the formation of each presentation signal is a 360* repetitive single-variable function of the difference between the angles theta and phi having a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle, and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 14

A signal-processing system for producing or reproducing directional audio information comprising encoding means for matrixing source signals representative of sounds from different bearing angles theta , each measured from a source reference direction, to form transmission signals having encoding mixing coefficients, at least one of said signals having encoding mixing coefficients substantially corresponding to values of a given single-variable function of the bearing angle theta of the respective sounds, decoding means for re-matrixing the transmission signals to form signals for presentation at bearing angles phi , each measured from a presentation reference direction having a specific angular relation to said source reference direction, said decoding means having means for multiplying each transmission signal by a decoding mixing coefficient substantially corresponding to the value of a single-variable function of phi for each presentation bearing angle, said function of phi being the complex conjugate of the function of theta defining the encoding mixing coefficients for each transmission signal, and means for adding the resultant product signals to form each presentation signal, so that the sum of all products of the function of theta applied to the source signals in formation of each transmission signal with the function of phi applied to that transmission signal in the formation of each presentation signal is a 360* repetitive single-variable function of the difference between the angles theta and phi having a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle, and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 15

In a signal-processing apparatus for reproducing directional audio information from a plurality of source signals to form a plurality of prEsentation signals, wherein the source signals are representative of sounds from different bearing angles theta , each measured from a source reference direction, to form transmission signals having encoding mixing coefficients, at least one of said signals having encoding mixing coefficients substantially corresponding to values of a given single-variable function of the bearing angle theta of the respective sounds, said apparatus comprising decoding means for re-matrixing the transmission signals to form signals for presentation at bearing angles phi , each measured from a presentation reference direction having a specific angular relation to said source reference direction, said decoding means having means for multiplying each transmission signal by a decoding mixing coefficient substantially corresponding to the value of a single-variable function of phi for each presentation bearing angle, said function of phi being the complex conjugate of the function of theta defining the encoding mixing coefficients for each transmission signal, and means for adding the resultant product signals to form each presentation signal, so that the sum of all products of the function of theta applied to the source signals in formation of each transmission signal with the function of phi applied to that transmission signal in the formation of each presentation signal is a 360* repetitive single-variable function of the difference between the angles theta and phi having a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle, and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 16

In a signal-processing apparatus for reproducing directional audio information from a plurality of source signals to form a plurality of prEsentation signals, wherein the source signals are representative of sounds from different bearing angles theta , each measured from a source reference direction, to form transmission signals having encoding mixing coefficients, at least one of said signals having encoding mixing coefficients substantially corresponding to values of a given single-variable function of the bearing angle theta of the respective sounds, said apparatus comprising decoding means for re-matrixing the transmission signals to form signals for presentation at bearing angles phi , each measured from a presentation reference direction having a specific angular relation to said source reference direction, said decoding means having means for multiplying each transmission signal by a decoding mixing coefficient substantially corresponding to the value of a single-variable function of phi for each presentation bearing angle, said function of phi being the complex conjugate of the function of theta defining the encoding mixing coefficients for each transmission signal, and means for adding the resultant product signals to form each presentation signal, so that the sum of all products of the function of theta applied to the source signals in formation of each transmission signal with the function of phi applied to that transmission signal in the formation of each presentation signal is a 360* repetitive single-variable function of the difference between the angles theta and phi having a maximum absolute value at a reference difference angle, a relatively small absolute value at the diametrically opposite difference angle, and absolute values at intermediate angles symmetrical with respect to the axis thus defined.

Claim 17

The method of claim 4 for producing two transmission signals wherein the transmission signals are formed as one of the following pairs:

Claim 18

The method of claim 3 for producing presentation signals from two transmission signals TL and TR wherein each presentation signal Pi is formed from the transmission signals by mixing thereof in the amplitude and phase relation Pi TL (1 + e j ( /2))) + TR (1 - e j ( /2)) where phi i is the bearing angle between a presentation location i and a laterally central reference location and j is the square root of -1.

Claim 19

The improved method of claim 6 wherein said function is proportional to the quantity 1 + ej , where Alpha is the angle between the source direction and the presentation direction and j is the square root of -1.

Claim 20

The improved method of claim 6 for stereo-compatible and mono-compatible reproduction wherein there are two transmission signals TL and TR formed from n source signals substantially as follows:

Claim 21

The improved method of claim 6 for stereo-compatible and mono-compatible reproduction wherein there are two transmission signals T and T formed from n source signals substantially as follows:

Claim 22

The method of claim 6 for reproduction of four source signals corresponding to mutually orthogonal sound locations by presentation to a listener from these same mutually Orthogonal locations wherein each presentation signal contains the corresponding-location source signal plus each of the adjacent-location source signals, both of the latter being reduced to 0.707 in relative amplitude, and one of them being advanced in relative phase by 45* and the other being retarded in relative phase by 45*, with respect to the corresponding location signal.

Claim 23

The method of claim 11 wherein the sound locations are at left, front, right and back, the corresponding source signals being SL, SF, SR and SB, and the corresponding presentation signals being PL, PF, PR and PB, respectively, and the transmission signals being TL and TR, the first sets of coefficients being: TL SL + 0.707 SF +45* + 0.707 SB -45*TR SR + 0.707 SF -45* + 0.707 SB +45* and the second sets of coefficients being: PL TL 0*PF 0.707 TL -45* + 0.707 TR +45*PR TR 0*PB 0.707 TL +45* + 0.707 TR -45*

Claim 24

The method of claim 14 wherein the sound locations are at left front, right front, right back and left back, the corresponding source signals being SLF, SRF, SRB and SLB, and the corresponding presentation signals being PLF, PRF, PRB and PLB, respectively, and the transmission signals being TL and TR, the first sets of coefficients being: TL 0.924 SLF +22 + 0.383 SRF +67+ 0.383 SRB -67 + 0.924 SLB -22TR 0.383 SLF -67 + 0.924 SRF -22+ 0.924 SRB +22 + 0.383 SLB +67 and the second sets of coefficients being: PLF 0.924 TL -22 + 0.383 TR +67PRF 0.383 TL -67 + 0.924 TR +22 1/2 *PRB 0.383 TL +67 + 0.924 TR -22PLB 0.924 TL +22 + 0.383 TR -67

Claim 25

The signal-processing apparatus of claim 1 comprising an encoder having input sound-source signals of various bearing angles and output transmission signals.