US 5,862,227 AGranted

Sound recording and reproduction systems

AssigneeAdaptive Audio Limited

InventorsFelipe Orduna-Bustamante, Ole Kirkeby, Hareo Hamada, Philip Arthur Nelson

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Abstract

A method of recording sound for reproduction by a plurality of loudspeakers, or for processing sound for reproduction by a plurality of loudspeakers, is described in which some of the reproduced sound appears to a listener to emmanate from a virtual source which is spaced from the loudspeakers. A filter means (H) is used either in creating the recording, or in processing the recorded signals for supply to loudspeakers, the filter means (H) being created in a filter design step in which: a) a technique is employed to minimise error between the signals (w) reproduced at the intended position of a listener on playing the recording through the loudspeakers, and desired signals (d) at the intended position, wherein: b) said desired signals (d) to be produced at the listener are defined by signals (or an estimate of the signals) that would be produced at the ears of (or in the region of) the listener in said intended position by an source at the desired position of the virtual source. A least squares technique may be employed to minimise the time averaged error between the signal reproduced at the intended position of a listener and the desired signal, or it may be applied to the frequency domain.

A method of recording sound for reproduction by a plurality of loudspeakers, or for processing sound for reproduction by a plurality of loudspeakers, in which some of the reproduced sound appears to a listener to emanate from a virtual source which is spaced from the loudspeakers, comprises utilizing filter means in creating the recording, or in processing the signals for supply to loudspeakers, the filter means being created by two filter design steps, comprising:

(a) specifying, in the form of filters (A), the transfer functions between said desired position of the virtual source and specific positions in the reproduced sound field which are at the ears of the listener or in the region of the listener's head;
and
(b) convolving said transfer function filters (A) with a matrix of cross-talk cancellation filters (H.sub.x) used to invert the electro-acoustic transmission path or paths (C) between loudspeaker inputs and said specific positions, said matrix of cross-talk cancellation filters (H.sub.x) being created in filter design steps for a multi-channel system, the creation comprising:
(i) measurement of the impulse response of all the electro-acoustic transmission paths using a matrix of elements C(n), and employing zero-padding of said elements C(n) to ensure that the duration of the impulse responses are N.sub.h samples;
(ii) calculation of the DFTs of the zero-padded impulse responses so as to give a matrix of frequency responses C(k) at N.sub.h evenly spaced points;
(iii) calculation of the frequency responses of the filters at the N.sub.h frequencies from the expression C.sup.H (k)C(k)+.beta.I!.sup.-1 C(k), where superscript "H" denotes the Hermitian transpose operator, "I" denotes the Identity matrix and .beta. is a regularizing parameter;
(iv) calculation of the matrix of inverse DFTs of said expression;
and
(v) calculation of the impulse responses of the filters by swapping the first and second half of the inverse FFTs of each of the elements of the matrix of inverse DFTs, implementing a modeling delay of (N.sub.h /2)+1 samples.

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Facts

Application

08/793,542Filed 25 Jul 1997

Priority

GB 941718525 Aug 1994

Granted

19 Jan 1999

Term ends

Not estimatedThe source records don’t support an estimate.

Classification6 codes

H04S 1/002
Two-channel systems: non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution
H04S 1/007
Two-channel systems: in which the audio signals are in digital form
H04S 3/002
Systems employing more than two channels, e.g. quadraphonic: non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound…
H04S 1/005
Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution: for headphones

Abstract

Claims14