US3760102A
Expired / Lapsed
US
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Level setting in noise reduction systems
Assignee: DOLBY LABOR INC US
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Filing: 1971-10-26
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Granted: 1973-09-18
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Expires: 1991-10-26
Abstract
Abstract A special test tone at a predetermined level is recorded or transmitted to enable the level to be set correctly on playback or reception. To enable the tone to be identified, it is intermittently and briefly frequency modulated to give the aural impression of a constant tone with intermittent ''''blips'''' therein. Because the amplitude stays constant, the modulation does not interfere with level meters and the like.
Inventors
- 👤 D Robinson
- 👤 R Dolby
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 23:11
CPC Classifications
H; H03; H03G; H03G7/00; H03G7/002; G; G11; G11B; G11B20/00; G11B20/24
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
120 words
In an audio system having an input, a test tone generator, and switching means for selectively connecting the input to receive an audio input signal or the output of said generator, the improvement wherein said generator comprises: a constant amplitude audio oscillator having a base frequency of some hundreds of Hertz, and modulating means permanently connected to the oscillator for intermittently and briefly frequency-modulating the oscillator without changing the amplitude of the signal generated thereby, wherein said modulating means shift the oscillator frequency from the base frequency to a different frequency during first intervals of low tens of milliseconds in duration, the intervening intervals during which the oscillator is at the base frequency being substantially longer than the first intervals.
Claim 2
Dependent Claim
120 words
In an audio system having an input, a test tone generator, and switching means for selectively connecting the input to receive an audio input signal or the output of said generator, the improvement wherein said generator comprises: a constant amplitude audio oscillator having a base frequency of some hundreds of Hertz, and modulating means permanently connected to the oscillator for intermittently and briefly frequency-modulating the oscillator without changing the amplitude of the signal generated thereby, wherein said modulating means shift the oscillator frequency from the base frequency to a different frequency during first intervals of low tens of milliseconds in duration, the intervening intervals during which the oscillator is at the base frequency being substantially longer than the first intervals.
Claim 3
Dependent Claim
83 words
A noise reduction unit comprising compressor/expander circuitry having an input and an output, a switch for setting said circuitry selectively to compressor mode or expander mode, a signal input terminal, a test tone generator having an output terminal, and switching means for selectively connecting said input terminal or said generator output terminal to said circuitry input, said generator comprising: a constant amplitude audio oscillator, and modulating means for intermittently and briefly frequency-modulating the oscillator without changing the amplitude of the signal generated thereby.
Claim 4
Dependent Claim
83 words
A noise reduction unit comprising compressor/expander circuitry having an input and an output, a switch for setting said circuitry selectively to compressor mode or expander mode, a signal input terminal, a test tone generator having an output terminal, and switching means for selectively connecting said input terminal or said generator output terminal to said circuitry input, said generator comprising: a constant amplitude audio oscillator, and modulating means for intermittently and briefly frequency-modulating the oscillator without changing the amplitude of the signal generated thereby.
Claim 5
Dependent Claim
23 words
A system according to claim 2, wherein said modulating means change the oscillator frequency by an amount of the order of 10 percent.
Claim 6
Dependent Claim
15 words
A system according to claim 3, wherein said modulating means shift the oscillator frequency upwardly.
Claim 7
Dependent Claim
23 words
A system according to claim 3, wherein said modulating means modulate the oscillator frequency abruptly between two frequencies differing by approximately 10 percent.
Claim 8
Dependent Claim
20 words
A system according to claim 2, wherein the modulating means have a period in the range 0.5 to 1.5 seconds.
Claim 9
Dependent Claim
30 words
A system according to claim 2, wherein the oscillator comprises a constant-amplitude, free-running multivibrator generating square waves, and a shaping circuit for forming a sinusoidal signal from the square waves.
Claim 10
Dependent Claim
53 words
A noise reduction unit according to claim 2, wherein said modulating means shift the oscillator frequency from a base frequency to a different frequency during first intervals of low tens of milliseconds in duration, the intervening intervals during which the oscillator is at the base frequency being substantially longer than the first intervals.
Claim 11
Dependent Claim
30 words
A noise reduction unit according to claim 8, wherein the base frequency is some hundreds of Hz and the different frequency is approximately 10 percent higher than the base frequency.
Claim 12
Dependent Claim
14 words
A system according to claim 9, wherein the base frequency is approximately 850 Hz.
Claim 13
Dependent Claim
14 words
A system according to claim 9, wherein the base frequency is approximately 400 Hz.
Claim 14
Dependent Claim
18 words
A noise reduction unit according to claim 14, wherein the modulating means is permanently connected to the oscillator.
Claim 15
Dependent Claim
91 words
A noise reduction unit comprising compressor/expander circuitry having an input and an output, a switch for setting said circuitry selectively to compressor mode or expander mode, a signal input teRminal, a test tone generator having an output terminal, and switching means for selectively connecting said input terminal or said generator output terminal to said circuitry input, said generator comprising: a constant amplitude audio oscillator having a base frequency greater than 500 Hz, and modulating means for intermittently and briefly frequency-modulating the oscillator without changing the amplitude of the signal generated thereby.
Claim 16
Dependent Claim
91 words
A noise reduction unit comprising compressor/expander circuitry having an input and an output, a switch for setting said circuitry selectively to compressor mode or expander mode, a signal input teRminal, a test tone generator having an output terminal, and switching means for selectively connecting said input terminal or said generator output terminal to said circuitry input, said generator comprising: a constant amplitude audio oscillator having a base frequency greater than 500 Hz, and modulating means for intermittently and briefly frequency-modulating the oscillator without changing the amplitude of the signal generated thereby.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-09-17 | 1977-03-19 | 1977-09-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-17 | 1981-03-19 | 1981-09-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-17 | 1985-03-19 | 1985-09-18 | $7700.00 | Window Closed / Lapsed |