Electrical audio signal processing systems and devices – Including frequency control – Having automatic equalizer circuit
Patent
1993-08-03
1996-04-23
Isen, Forester W.
Electrical audio signal processing systems and devices
Including frequency control
Having automatic equalizer circuit
381 59, 381 98, H03G 500
Patent
active
055111297
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to filtering audio signals to compensate the effects of acoustic and/or electrical stages in the signal path from the original sound source to the human ear.
2. Discussion of Prior Art
In general, this signal path will include a pickup receiving the sound, and converting it to, typically, an electrical signal; signal transmission channels; signal processing (e.g. filtering, tone control or noise reduction); signal transmission, or alternatively recording on to a record carrier; signal reception or alternatively replaying from the record carrier; a further transmission link; and reconversion into an audio signal via an electro-acoustic transducer. If the transducer is a loudspeaker, the final stage in the path is transmission through an acoustic environment (typically a room) to the human ear.
Associated with each stage of the signal path is a transfer characteristic, and at various stages in the path attempts may be made to filter the signal to compensate the effects of these transfer characteristics. Compensation generally takes place at a stage in the signal path subsequent to the stages to be compensated. For example, in the case of a sound recording, the signal will be filtered at the mixing and cutting stages so as to compensate, if necessary, for the recording environment and equipment (amongst other things).
At the reproduction stage, it is nowadays common to provide a so called "graphic equalizer" comprising a plurality of band pass filters each with its own gain control, though which the signal is passed, to allow a listener to re-equalize the reproduced sound signal. The graphic equalizer is generally positioned between the record carrier reader (e.g. turntable or compact disc player) and the power amplifier driving the electro-acoustic transducer (loudspeaker).
Since such equalizers are adjusted manually, their setting is a matter for the personal taste of the listener but they can be used (and are intended for use) to compensate for large scale irregularities in the amplitude response over frequency of the electro-acoustic transducer or of the acoustic environment in which the transducer is positioned.
In fact, with modern high fidelity audio equipment, the major variations in sound reproduction quality are due to the transfer functions of the loudspeaker and of the acoustic environment in which the loudspeaker is positioned.
The loudspeaker often comprises several separate transducers responsive to different frequency ranges, the loudspeaker input signal being split into the ranges by a crossover network (generally an analogue filter), and the transducers being mounted in a cabinet. The transfer function of the loudspeaker will thus depend upon the electrical characteristics of the crossover network and of the transducers; on the relevant positions of the transducers; and on the mechanical resonances of the cabinet.
The transfer function of the acoustic environment may be visualised by considering that the signal passes though multiple paths between the loudspeaker and the human ear; as well as the direct path through the air between the two, there will generally be a path through the floor on which the loudspeaker and user stand, and reflected paths from the (at least) four walls, ceiling and floor. This leads to constructive and destructive acoustic interference and to standing wave patterns of considerable complexity within the room, so that the paths from the loudspeaker to different points in the room will have different transfer characteristics--where the room exhibits pronounced resonances, these transfer characteristics can be extremely different, with complete cancellation at some frequencies, the frequencies differing between different points. These effects are audible as colorations of the reproduced sound, and as relatively long reverberations.
It would in principle be desirable to provide a compensating filter and means for deriving the parameters of the filter such that a given sound source would be rep
REFERENCES:
patent: 4631749 (1986-12-01), Rapaich
patent: 4694498 (1987-09-01), Suzuki et al.
patent: 4888808 (1989-12-01), Ishikawa et al.
patent: 5168129 (1992-12-01), D'Antonio
patent: 5185805 (1993-02-01), Chiang
Journal of the Audio Engineering Society, vol. 37, No. 11, Nov. 1989, New Yourk US pp. 919-926, Kuriyama et al `Adaptive Loudspeaker System`.
Patent Abstracts of Japan, vol. 13, No. 38 (E-709) 27 Jan. 1989 & JP, A, 63 234 699 (Matsushita) 26 Sep. 1988 (abstract only).
IEEE Acoustics, Speech, and Signal Processing Magazine, vol. 36, No. 2, Feb. 1988, New York US pp. 145-152.
Patent Abstracts of Japan, vol. 9, No. 99 (E-311) 27 Apr. 1985 & JP, A,59 225 626 (Nippon) 18 Dec. 1984 (abstract only).
1989 IEEE Int. Symposium on Circuits and Systems Portland 8-11 May 1989; Phuong-Quan Hoang et al pp. 371-374.
Journal of the Audio Engineering Society, vol. 37, No. 11, Nov. 1989, New York US pp. 899-907.
Patent Abstracts of Japan, vol. 13, No. 594 (E-867) 27 Dec. 1989 & JP,A,12 048 798 (Toa Tokushu) 4 Oct. 1989 (abstract only).
Craven Peter G.
Gerzon Michael A.
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