Methods and apparatus for producing directional sound

Claim 1

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) applying the filter function for a selected position as a filter to the signal representing sound to produce a filtered signal; and (d) converting the filtered signal to a sound and applying the sound to the ear of a listener.

Claim 2

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) applying the filter function for a selected position as a filter to the signal representing sound to produce a filtered signal; and (d) converting the filtered signal to a sound and applying the sound to the ear of a listener.

Claim 6

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only..of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) applying the filter function for a selected position as a filter to the signal representing sound to produce a filtered signal; and (d) converting the filtered signal to a sound and applying the sound to the ear of a listener; wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU7## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions.

Claim 7

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only..of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) applying the filter function for a selected position as a filter to the signal representing sound to produce a filtered signal; and (d) converting the filtered signal to a sound and applying the sound to the ear of a listener; wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU7## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions.

Claim 9

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time, wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU8## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions; (c) applying the filter function for a selected position as a filter to the signal representing sound to produce a filtered signal; and (d) converting the filtered signal to a sound and applying the sound to the ear of a listener, wherein the step of determining a model filter function H(θ,φ) includes the steps of: (1) forming for the selected number N an N dimensional vector H(θ j ,φ k ) having elements which are N samples in frequency of the measured filter functions at the measured positions (θ j ,φ k ), where j=1, . . . , L, k=1, . . . , M, and L and M are the total number of azimuth and elevation positions, respectively, at which measurements were made; (2) forming a covariance matrix Σ H as ##EQU9## where H is the sample mean determined as: ##EQU10## and where the superscript " H " denotes the complex conjugate transpose of the matrix and α j ,k is a selected non-negative weighting factor; (3) determining the basic filter functions t i , i=1, 2, . . . , p, to satisfy the relation: Σ.sub.H t.sub.i =λ.sub.i t.sub.i where λ i , i=1, 2, . . . , p, are the "p" largest eigenvalues of the matrix Σ H and wherein t o =H.

Claim 10

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time, wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU8## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions; (c) applying the filter function for a selected position as a filter to the signal representing sound to produce a filtered signal; and (d) converting the filtered signal to a sound and applying the sound to the ear of a listener, wherein the step of determining a model filter function H(θ,φ) includes the steps of: (1) forming for the selected number N an N dimensional vector H(θ j ,φ k ) having elements which are N samples in frequency of the measured filter functions at the measured positions (θ j ,φ k ), where j=1, . . . , L, k=1, . . . , M, and L and M are the total number of azimuth and elevation positions, respectively, at which measurements were made; (2) forming a covariance matrix Σ H as ##EQU9## where H is the sample mean determined as: ##EQU10## and where the superscript " H " denotes the complex conjugate transpose of the matrix and α j ,k is a selected non-negative weighting factor; (3) determining the basic filter functions t i , i=1, 2, . . . , p, to satisfy the relation: Σ.sub.H t.sub.i =λ.sub.i t.sub.i where λ i , i=1, 2, . . . , p, are the "p" largest eigenvalues of the matrix Σ H and wherein t o =H.

Claim 12

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) determining an interpolated model filter function for sound originating at a selected position between positions at which measurements were made which has the same form as the model filter functions determined for the measured positions including the same basic filter functions and with the weights for the basic filter functions determined as an interpolated function of the weights for the model filter functions at the measured positions; (d) applying the interpolated model filter function for the selected position as a filter to the signal representing sound to produce a filtered signal; and (e) converting the filtered signal to a sound and applying the sound to the ear of a listener; wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU11## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions.

Claim 13

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) determining an interpolated model filter function for sound originating at a selected position between positions at which measurements were made which has the same form as the model filter functions determined for the measured positions including the same basic filter functions and with the weights for the basic filter functions determined as an interpolated function of the weights for the model filter functions at the measured positions; (d) applying the interpolated model filter function for the selected position as a filter to the signal representing sound to produce a filtered signal; and (e) converting the filtered signal to a sound and applying the sound to the ear of a listener; wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU11## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions.

Claim 15

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) determining an interpolated model filter function for sound originating at a selected position between positions at which measurements were made which has the same form as the model filter functions determined for the measured positions including the same basic filter functions and with the weights for the basic filter functions determined as an interpolated function of the weights for the model filter functions at the measured positions; (d) applying the interpolated model filter function for the selected position as a filter to the signal representing sound to produce a filtered signal; and (e) converting the filtered signal to a sound and applying the sound to the ear of a listener.

Claim 16

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time; (c) determining an interpolated model filter function for sound originating at a selected position between positions at which measurements were made which has the same form as the model filter functions determined for the measured positions including the same basic filter functions and with the weights for the basic filter functions determined as an interpolated function of the weights for the model filter functions at the measured positions; (d) applying the interpolated model filter function for the selected position as a filter to the signal representing sound to produce a filtered signal; and (e) converting the filtered signal to a sound and applying the sound to the ear of a listener.

Claim 20

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time, wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU12## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions; (c) determining an interpolated model filter function for sound originating at a selected position between positions at which measurements were made which has the same form as the model filter functions determined for the measured positions including the same basic filter functions and with the weights for the basic filter functions determined as an interpolated function of the weights for the model filter functions at the measured positions; (d) applying the interpolated model filter function for the selected position as a filter to the signal representing sound to produce a filtered signal; and (e) converting the filtered signal to a sound and applying the sound to the ear of a listener; wherein the step of determining a model filter function H(θ,φ) includes the steps of: (1) forming for the selected number N, an N dimensional vector H(θ j ,φ k ) having elements which are N samples in frequency of the measured filter functions at the measured positions (θ j ,φ k ), where j=1, . . . , L, k=1, . . . , M, and L and M are the total number of azimuth and elevation positions, respectively, at which measurements were made; (2) forming a covariance matrix Σ H as ##EQU13## where H is the sample mean determined as: ##EQU14## and where the superscript " H " denotes the complex conjugate transpose of the matrix and α j ,k is a selected non-negative weighting factor; (3) determining the basic filter functions t i , i=1, 2, . . . , p, to satisfy the relation: Σ.sub.H t.sub.i =λ.sub.i t.sub.i where λ i , i=1, 2, . . . , p, are the "p" largest eigenvalues of the matrix Σ H and wherein t o =H.

Claim 21

A method of modifying a signal representing a sound which is to be applied as a sound to a listener's ear to simulate the origin of that sound at a selected position in space with respect to the listener's ear, comprising the steps of: (a) measuring the filter function for sound originating from a sound source at a plurality of discrete positions in the space surrounding an origin position at which the sound is measured, the measurement position corresponding to the position of a listener's ear; (b) determining a model filter function for each position at which sound originates which approximates in both magnitude and phase the actual measured filter function at each position, the model filter function formed as a sum of a selected number of basic filter functions which are functions only of frequency or time and not of position, with each basic filter function multiplied by a weighting factor for that basic filter function which is a function only of the position at which the sound originated and not of frequency or time, wherein the model filter functions are determined for a selected number N of samples in frequency of the measured filter functions, and wherein the model filter function for an azimuth position θ and an elevation position φ of sound origination in a spherical coordinate system about the position of sound measurement as the origin has the form ##EQU12## where the model filter function H(θ,φ) is an N dimensional vector, t i is an N dimensional vector representing the basic filter functions, w i (θ,φ) are the weighting factors, and p is a selected number of basic filter functions; (c) determining an interpolated model filter function for sound originating at a selected position between positions at which measurements were made which has the same form as the model filter functions determined for the measured positions including the same basic filter functions and with the weights for the basic filter functions determined as an interpolated function of the weights for the model filter functions at the measured positions; (d) applying the interpolated model filter function for the selected position as a filter to the signal representing sound to produce a filtered signal; and (e) converting the filtered signal to a sound and applying the sound to the ear of a listener; wherein the step of determining a model filter function H(θ,φ) includes the steps of: (1) forming for the selected number N, an N dimensional vector H(θ j ,φ k ) having elements which are N samples in frequency of the measured filter functions at the measured positions (θ j ,φ k ), where j=1, . . . , L, k=1, . . . , M, and L and M are the total number of azimuth and elevation positions, respectively, at which measurements were made; (2) forming a covariance matrix Σ H as ##EQU13## where H is the sample mean determined as: ##EQU14## and where the superscript " H " denotes the complex conjugate transpose of the matrix and α j ,k is a selected non-negative weighting factor; (3) determining the basic filter functions t i , i=1, 2, . . . , p, to satisfy the relation: Σ.sub.H t.sub.i =λ.sub.i t.sub.i where λ i , i=1, 2, . . . , p, are the "p" largest eigenvalues of the matrix Σ H and wherein t o =H.