Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1982-10-18
1985-05-14
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
455249, H04N 560
Patent
active
045176027
ABSTRACT:
A dynamic noise filter especially adapted for use in audio reproduction systems within a television display device is provided to eliminate perceived noise. An audio signal having a relatively wide frequency range is passed through a variable bandwidth lowpass filter, the upper frequency cutoff point being variable in response to a control signal. A control path includes a filter and detector circuit for generating the control signal in response to the amplitude of the audio signal within an upper frequency portion of the audio signal frequency range. The control signal controls the bandwidth of the lowpass filter inversely with respect to the level of the audio signal within the upper frequency portion of the frequency range. A further filter is included in the control path for providing substantial attenuation at the fundamental frequency and lower order harmonic frequencies of the television horizontal line scanning signal in order to prevent the control path from erroneously responding to this signal.
REFERENCES:
patent: 3543191 (1970-11-01), Plunkett
patent: 3678416 (1972-07-01), Burwen
patent: 3753159 (1973-08-01), Burwen
patent: 4239939 (1980-12-01), Griffis
National Semiconductor Datasheet Entitled "LM 1894 Dynamic Noise Reduction System DNR", by National Semiconductor Corp., Jan. 1982.
An Article Entitled "Audio Noise Reduction and Masking" by Martin Giles Distributed at the International Conference on Consumer Electronics held Jun. 1982, in Illinois.
National Semiconductor Linear Application Update, Document CLAU-129B, Issued Oct. 1981, pp. 11 and 19.
"Signals and Systems" by Alan V. Oppenheim and Alan S. Willsky, p. 424, published by Prentice-Hall, 1983.
"Analysis and Design of Analog Integrated Circuits" by Paul R. Gray and Robert G. Meyer, pp. 333-334, published by John Wiley & Sons, 1977.
Nationals Audio Handbook Data Sheet on AM, FM, and FM Stereo Section 3; "3.6.1 LM2111-LM1351 FM Amplifiers", pp. 3-13 Through 3-16, by National Semiconductor Corporation, 1976.
Hettiger James
Murphy, III Wesley W.
Chin Tommy P.
Edelman Lawrence C.
Emanuel Peter M.
Parker Michael D.
RCA Corporation
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