Adaptive control signal filter for audio signal expander

Details Adaptive control signal filter for audio signal expander Adaptive control signal filter for audio signal expander

1982-09-27

1984-08-14

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including gain control means

330136, 330141, H03G 320, H03G 342

Patent

active

044659814

ABSTRACT:
A resistance-capacitance filter smoothes the control voltage of an audio signal expander. An analog gate couples the greater, in a given sense, of the smoothed control voltage and a further voltage to the control terminal of a variable gain device in the audio signal path, the further voltage being equal to the filter input voltage less a constant equal to Vbe. A time constant modifier circuit reduces the filter time constant when the filter input voltage differs in either sense from the smoothed control voltage by a fraction, less than unity, of Vbe. The resultant, relatively "narrow" dead zones of the adaptive filter enable operation of the expander with relatively low signal voltage levels thereby enabling a corresponding reduction in supply voltage requirements and providing further advantages such as reduced power dissipation, reduced heat build-up and improved reliability.

REFERENCES:
patent: 3350512 (1967-10-01), Percival et al.
patent: 3732371 (1973-05-01), Burwen
patent: 3980964 (1976-09-01), Grodinsky
patent: 4220929 (1980-09-01), Talbot et al.
patent: 4377788 (1983-03-01), Christopher et al.
"High Fidelity Volume Expander", N. C. Pickering, Audio Engineering, Sep. 1947.
"$70 Decoder for New CX Records", J. Roberts, Popular Electronics, Jan. 1982, pp. 39-44.

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