Phase conversion surround circuitry

Details Phase conversion surround circuitry Phase conversion surround circuitry

2002-11-15

2004-09-07

Mei, Xu (Department: 2644)

Electrical audio signal processing systems and devices

Binaural and stereophonic

C381S307000, C381S097000

Reexamination Certificate

active

06788789

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to phase-conversion surround circuitry for sound-field reproduction used in audio system.
Audio systems for music-data reproduction from cassette tapes, CDs, MDs, memory cards, DVDS, etc., are usually equipped with a digital surround circuit or an analog phase-conversion (shift) surround circuit, for offering surround effects to create wide sound fields.
Shown in
FIG. 1
is a known analog phase-conversion surround circuit
20
equipped with phase-delay units
4
and
5
.
Input right- and left-channel audio signals R and L are supplied to two-stage phase (90°)-delay units
4
and
5
via low-frequency amplifiers (operational amplifiers)
1
,
2
and
3
.
A resultant 180°-delayed signal &Dgr;(R−L) is combined (added/subtracted) with the right- and left-channel audio signals R and L at low-frequency amplifiers (operational amplifiers)
7
and
8
, respectively, via an ON/OFF switch SW and an allotter
6
, thus composite signals R+&Dgr;(R−L) and L−&Dgr;(R−L) being output.
Three or more stages of the phase-delay units for longer delay time will enhance surround effects (wider sound fields). Nevertheless, the more enhanced surround effects, the more difference in sound quality based on addition/subtraction-resultant composite signals, so that most listeners feel low sound quality. For example, four-stage phase-delay units for 360°-delay could cause that most people cannot listen for a long time. On the contrary, one or two-stage phase-delay units for less delay act like an equalizer and reduce surround effects.
Moreover, the known phase-conversion surround circuit
20
gives a fixed level of surround effects, thus the created sound being not feasible for healing effects with BGM, quiet music, music with full of low-level sounds, etc.
SUMMARY OF THE INVENTION
A purpose of the present invention is to provide a phase-conversion surround circuitry with enhanced surround and healing effects.
The present invention provides a phase-conversion surround circuitry to give surround effects to right- and left-channel audio signals, including: a phase delayer to delay an audio difference signal between the right- and left-channel audio signals, thus outputting a delayed audio difference signal; a combiner to combine the delayed audio difference signal with the right- and left-channel audio signals, thus outputting composite audio signals; and a controller to oscillate at frequency of 12 Hz or less to periodically vary a time constant of the phase delayer.


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