Patent US2354453A successfully refreshed from Google Patents.
US4476502A
Expired / Lapsed
US
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Noise reduction system
Assignee: Hitachi Ltd
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Filing: 1982-08-27
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Granted: 1984-10-09
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Expires: 2002-08-27
Abstract
Abstract A noise reduction system is provided which can operate as either a Dolby B-type or C-type system. In either case, an input signal is applied to the variable impedance of a high-level side chain through an identical shared filter circuit network. The high-level side chain has two voltage-current converters for controlling the variable impedance. By substantially inhibiting the operation of one of the two converters, the system operates as a C-type Dolby system. On the other hand, when the system operates as a B-type Dolby system, a bias current is applied to each of the two converters during periods of no input signal. This bias current is about half of a minute bias control current which is applied during no signal periods to the single converter used when the system operates as the C-type Dolby system.
Inventors
- 👤 Kazuo Watanabe
- 👤 Yasuo Kominami
- 👤 Yoshiyuki Takizawa
- 👤 Akira Haeno
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 10:20
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/62; H04B1/64; H03; H03G; H03G9/00; H03G9/02; H03G9/025
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
144 words
A noise reduction system comprising: a first level processing circuit which has a first combining network, and a first signal inverter, an anti-saturation network and a low-level side chain coupled to said first combining network; a second level processing circuit which has a second combining network, and a second signal inverter, a spectral skewing network and a high-level side chain coupled to said second combining network; said low-level side chain including a first filter circuit network, a first variable impedance and a first voltage-current converter; said high-level side chain including a second filter circuit network, a second variable impedance and a second voltage-current converter and a third voltage-current converter whose characteristics are substantially equal to each other, and a control circuit coupled to said third voltage-current converter, said control circuit including means for selectively permitting or inhibiting an operation of said third voltage-current converter.
Claim 2
Dependent Claim
144 words
A noise reduction system comprising: a first level processing circuit which has a first combining network, and a first signal inverter, an anti-saturation network and a low-level side chain coupled to said first combining network; a second level processing circuit which has a second combining network, and a second signal inverter, a spectral skewing network and a high-level side chain coupled to said second combining network; said low-level side chain including a first filter circuit network, a first variable impedance and a first voltage-current converter; said high-level side chain including a second filter circuit network, a second variable impedance and a second voltage-current converter and a third voltage-current converter whose characteristics are substantially equal to each other, and a control circuit coupled to said third voltage-current converter, said control circuit including means for selectively permitting or inhibiting an operation of said third voltage-current converter.
Claim 3
Dependent Claim
172 words
A noise reduction system which can be operated either as a Dolby B-type or Dolby C-type system comprising: a first level processing circuit which has a first combining network, a first signal inverter, an anti-saturation network and a low-level side chain; a second level processing circuit which has a second combining network, a second signal inverter, a spectral skewing network and a high-level side chain; said low-level side chain including a first filter circuit network, a first variable impedance and a first voltage-current converter; said high-level side chain including a second filter circuit network, a second variable impedance and a second voltage-current converter and a third voltage-current converter whose characteristics are substantially equal to each other; means for inhibiting an operation of said third voltage-current converter to operate the noise reduction system as a Dolby C-type system; and means for reducing an impedance of said first variable impedance and for simultaneously operating said second voltage-current converter and said third voltage-current converter to operate the noise reduction system as a Dolby B-type system.
Claim 4
Dependent Claim
172 words
A noise reduction system which can be operated either as a Dolby B-type or Dolby C-type system comprising: a first level processing circuit which has a first combining network, a first signal inverter, an anti-saturation network and a low-level side chain; a second level processing circuit which has a second combining network, a second signal inverter, a spectral skewing network and a high-level side chain; said low-level side chain including a first filter circuit network, a first variable impedance and a first voltage-current converter; said high-level side chain including a second filter circuit network, a second variable impedance and a second voltage-current converter and a third voltage-current converter whose characteristics are substantially equal to each other; means for inhibiting an operation of said third voltage-current converter to operate the noise reduction system as a Dolby C-type system; and means for reducing an impedance of said first variable impedance and for simultaneously operating said second voltage-current converter and said third voltage-current converter to operate the noise reduction system as a Dolby B-type system.
Claim 5
Dependent Claim
84 words
A noise reduction system according to claim 2, wherein said noise reduction system includes means for setting a bias current flow through each of the second and third voltage-current converters during Dolby B-type operation when no input signal is received by said noise reduction system at a value of about half of a bias current which flows through said second voltage-current converter when said noise reduction system operates as the Dolby C-Type system when no input signal is received by said noise reduction system.
Claim 6
Dependent Claim
40 words
A noise reduction system according to claim 2 or 3, including means for maintaining the same filter parameters for said second filter network regardless of whether said noise reduction system operates as a type B or type C Dolby system.
Claim 7
Dependent Claim
44 words
A noise reduction system according to claim 4, wherein said second filter network includes a fixed value resistor and a fixed value capacitor coupled in parallel with one another between an input terminal for said noise reduction system and said second and third voltage-converters.
Claim 8
Dependent Claim
31 words
A noise reduction system according to claim 5, wherein said fixed value resistor has a value of b 47 kΩ and said fixed value capacitor has a value of 10,000 pF.
Claim 9
Dependent Claim
61 words
A noise reduction system according to claims 1, 2 or 3, wherein said low level side chain further includes a first signal amplifier, a first gain control amplifier, first rectifying diodes and a first overshoot suppressor, and wherein said high-level side chain further includes a second signal amplifier, a second gain control amplifier, second rectifying diodes and a second overshoot suppressor.
Claim 10
Dependent Claim
58 words
A noise reduction system according to claim 4, wherein said low level side chain further includes a first signal amplifier, a first gain control amplifier, first rectifying diodes and a first overshoot suppressor, and wherein said high-level side chain further includes a second signal amplifier, a second gain control amplifier, second rectifying diodes and a second overshoot suppressor.
Claim 11
Dependent Claim
58 words
A noise reduction system according to claim 5, wherein said low level side chain further includes a first signal amplifier, a first gain control amplifier, first rectifying diodes and a first overshoot suppressor, and wherein said high-level side chain further includes a second signal amplifier, a second gain control amplifier, second rectifying diodes and a second overshoot suppressor.
Claim 12
Dependent Claim
58 words
A noise reduction system according to claim 6, wherein said low level side chain further includes a first signal amplifier, a first gain control amplifier, first rectifying diodes and a first overshoot suppressor, and wherein said high-level side chain further includes a second signal amplifier, a second gain control amplifier, second rectifying diodes and a second overshoot suppressor.
References Cited (Backward Citations)
US4263624A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-10-09 | 1988-04-09 | 1988-10-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-10-09 | 1992-04-09 | 1992-10-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-10-09 | 1996-04-09 | 1996-10-09 | $7700.00 | Window Closed / Lapsed |