US 5,400,405 A · Audio image enhancement system

Abstract

Stereo processing circuitry is provided for modifying stereo signals so as to enhance the perception of imaging and ambience in non-ideal listening locations and confined environments such as the driver's location in a stereo-equipped vehicle. In a first modified mode, the stereo channels are symmetrically cross-coupled in additive polarity at high frequencies to enhance image localization, and in subtractive polarity over a full audio frequency spectrum to enhance stereo ambience. In a second modified mode, additional cascaded circuitry introduces frequency-selective polarity inversion and asymmetrical cross-coupling to compensate for the closer proximity of one of the loudspeakers to the listener's location, for the direct sound path from the nearer loudspeaker, and for the typical off-axis orientation of the nearer loudspeaker relative to the listener's position. In this second mode, the overall stereo listening effects including channel amplitude balances correction of acoustic polarity, equalization of off-axis loudspeaker frequency response, stereo ambience effect and image realization are optimized for a predetermined listening location. A three-position switching system allows selection of normal stereos the first modified mode or the second modified mode. The signal processing circuitry for implementing the second modified mode may be configured by a selection of modular op-amp filter and signal summing circuit blocks which perform frequency-dependent polarity inversion and, in a preferred embodiment, asymmetrical channel cross-coupling.

Claims24

Dependent claims

Stereophonic audio processing circuitry for modifying an input stereo signal pair, consisting of an A-channel input signal and a B-channel input signal, in a manner to provide a processed stereo signal pair for producing via stereo output amplifiers and loudspeakers a modified acoustic field providing ambience enhancement and image enhancement, said circuitry comprising:

an input processor, receiving the input stereo signal pair, comprising:
a high-pass cross-coupling circuit having a frequency-dependent branch providing high frequency channel-to-channel cross-coupling in additive polarity and in a predetermined amount;
and
a broad-band cross-coupling circuit, having at least one broad-band cross-coupled signal path providing broad-band channel-to-channel cross-coupling in subtractive polarity;
said input processor being made to provide as output a first modified stereo signal pair, consisting of a first modified A-channel signal and a first modified B-channel signals wherein additive cross-coupling is introduced in a high frequency range for imaging enhancement, and subtractive cross-coupling is introduced over a broad frequency range for enhanced recorded sound ambient information.

2 more elements

Stereophonic audio processing circuitry, in a stereo system operating with an A-channel signal and a B-channel signal, for modifying the A-channel signal, comprising;

a low pass filter receiving as input the A-channel signal and providing as output a low frequency audio signal;
a high pass filter receiving as input the A-channel signal and providing as output a high frequency audio signal;
and
summing means receiving at a first input the high frequency audio signal, at a second input the low frequency audio signal and at a third input an attenuated replica of the B-channel input signal, said summing means providing an output constituting the modified A-channel signal consisting of a summation of the signals received at the first, second and third inputs in predetermined proportions, wherein high frequency output components deriving from the second input are made to be opposite in polarity to high frequency components deriving from the third input;
whereby, through frequency-selective polarity-inversion and asymmetrical cross-coupling, the modified A-channel signal is caused to include a low frequency audio component, a high frequency audio component and an attenuated cross-coupled B-channel signal component of predetermined proportion having in a high frequency range thereof a polarity opposite that of the high frequency audio component.

2 more elements

A method of processing an input stereo signal pair, consisting of an A-channel input signal and a B-channel input signal, to derive a processed stereo signal pair for producing via stereo loudspeakers a modified acoustic field for ambience and image enhancement at an asymmetrical listening location, comprising the audio signal processing steps of:

(a) additively cross-coupling a predetermined channel-to-channel signal portion symmetrically over a predetermined high frequency audio range;
(b) subtractively cross-coupling a predetermined channel-to-channel signal portion symmetrically over a full frequency audio range;
(c) providing a first modified stereo signal comprising a first modified A-channel signal and a first modified B-channel signal which have been processed according to steps (a) and (b);
(d) low-pass and high-pass filtering the first modified A-channel signal to derive a low frequency audio signal and derive a high frequency audio signal which is inverted in polarity relative to the low frequency audio signal;
and
(e) summing the low frequency audio signal, the high frequency audio signal and the B-channel input signal in predetermined proportions and polarity so as to provide as output a second modified A-channel signal wherein a cross-coupled B-channel high frequency signal component is made to be opposite in polarity to a high frequency A-channel signal component.

3 more elements

Dependencies are inferred from the claim text.

Audio image enhancement system

Life of this patent

Audio image enhancement system

Life of this patent

Abstract

Claims24