Sound recording and reproduction systems

Details Sound recording and reproduction systems Sound recording and reproduction systems

1997-07-25

1999-01-19

Isen, Forester W.

Electrical audio signal processing systems and devices

Binaural and stereophonic

Pseudo stereophonic

H04S 500

Patent

active

058622276

DESCRIPTION:

BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase of International Application No. PCT/GB95/02005, filed Aug. 24, 1995, designating, the United States.
This invention relates to sound recording and reproduction systems.


INTRODUCTION

The invention provides a new method for recording and reproducing sound. The method described is based in general on the use of multi-channel digital signal processing techniques and can be directly applied to the improvement of methods used to create recordings for the subsequent reproduction of sound by two or more loudspeakers using conventional multi-channel reproduction systems. The techniques used can also be extended to process conventionally recorded sound signals for reproduction by multiple loudspeakers, and the recorded signal could on occasion be a single channel signal.
The general approach of using digital filters during reproduction to process recorded signals in order to improve the reproduction of those techniques in order to compensate for poorly positioned loudspeakers used to reproduce existing two-channel recordings has also been described in loudspeaker positions was introduced. The signal processing scheme used filters to operate on the recorded signals during reproduction in order to ensure that the sum of the time averaged squared errors between the reproduced signals and the "desired" signals were minimised. The desired signals were in turn specified as those in the sound field that would be produced by a source of sound in a particular specified position. With the filters in operation, then the signals reproduced would give a good match to the desired signals, thereby creating the illusion in a listener of sound emanating from the position of the "virtual source".
The present invention again utilises the notion of a virtual source. An object of the present invention is to provide a means for recording sound for reproduction via two (or more) loudspeakers in order to create the illusion in a listener of sound appearing to come from a specified spatial position, which can be remote from the actual positions of the loudspeakers.
A technique for achieving this objective during reproduction was first production of "arbitrarily located sound images with only two loudspeakers". In their invention, entitled the "Apparent sound source translator " Atal and Schroeder also used filter networks to operate on a single signal prior to its input to two loudspeakers.
According to one aspect of the present invention we provide 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 utilising filter means (H) in creating the recording, or in processing the signals for supply to loudspeakers, the filter means (H) being created in a filter design step, the filter design step being characterised by: reproduced at the intended position of a listener on playing the recording through the loudspeakers, and desired signals (d) at the intended position. wherein 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 a source at the desired position of the virtual source.
Preferably the desired signals are, in turn, deduced by 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.
The transfer functions could be derived in various ways, but preferably the transfer functions are deduced by first making measurements between the input to a real source and the outputs from microphones at the ears of (or in the region of) a dummy head used to model the effect of the "Head Related Transfer Functions" (HRTF) of the listener.
A least squares tech

REFERENCES:
patent: 5404406 (1995-04-01), Fuchigami et al.
patent: 5521981 (1996-05-01), Gehring
patent: 5727066 (1988-03-01), Elliott et al.

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