Amplifiers – Signal feedback – Variable impedance in feedback path varied by separate...
Reexamination Certificate
1999-09-16
2001-01-09
Pascal, Robert (Department: 2817)
Amplifiers
Signal feedback
Variable impedance in feedback path varied by separate...
C330S110000, C381S121000
Reexamination Certificate
active
06172561
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to electronic circuits, and more particularly to a high volume expander circuit for restoring the wide dynamic signal range of an audio signal.
Various mediums such as TV, FM and two-track VCR utilize audio signals that have a limited dynamic signal range due to signal format requirements. Such signal formats require that the audio signals at high levels be limited to a predetermined level before being either transmitted or recorded. Due to this, a sound track from a TV broadcast or VCR will not have the same wide dynamic sound as that heard in a movie theater.
In view of the above, devices have been developed to restore the wide dynamic sound of such mediums. One such device is known as a linear volume expander. However, since this device is linear, the audio signals will be expanded at high voltage levels as well as lower levels. This large amount of expansion is undesirable since the sound produced can be unpleasant to the listener. Therefore, it would be desirable to perform volume expansion at high signal levels only.
SUMMARY OF THE INVENTION
The present invention is directed to a circuit for performing volume expansion on an audio signal. The circuit includes an amplifier that has an input side and an output side. Further, the amplifier amplifies the audio signal at a first amplification to produce an amplified signal at the output side of the amplifier. The circuit also includes a shunting element coupled across the input side and output side of the amplifier. The shunting element includes a variable impedance device for changing the first amplification of the amplifier to a second amplification if the amplified signal reaches a predetermined threshold.
The present invention is also directed to a method for performing volume expansion on an audio signal. The method includes amplifying the audio signal at a first amplification to produce an amplified signal. Further, defining a predetermined threshold and then changing the first amplification to a second amplification if the amplified signal reaches the predetermined threshold.
REFERENCES:
patent: 3714588 (1973-01-01), Deboo et al.
patent: 3723894 (1973-03-01), Benenati
patent: 3757254 (1973-09-01), Takahashi et al.
patent: 3798562 (1974-03-01), Takahashi et al.
patent: 3911371 (1975-10-01), Nakamura et al.
patent: 4181896 (1980-01-01), Schroder
patent: 4450413 (1984-05-01), Fujibayashi
patent: 5936470 (1999-08-01), Stroud
“Program Multichannel Audio Gain”, James Sherwin, Electronic Design 3, Feb. 1, 1975, pp. 68-72.
DBX Model 118, Dynamic Range Enhancer Instruction Manual.
Choe Henry
Gross Russell
Pascal Robert
Philips Electronics N.A. Corp.
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