US3699271A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Speech processor using multiband controlled center clipping
Assignee: AT&T Inc
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Filing: 1970-11-16
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Granted: 1972-10-17
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Expires: 1990-11-16
Abstract
Abstract An echo suppressor for full duplex telephone circuits consists of a filter bank of contiguous band filters in the transmission path, with each filter output feeding a separate center clipper. Each clipping level is controlled by echo signal amplitude as attenuated by the trans-hybrid loss that occurs in the corresponding subband. The scheme permits ''''double-talking'''' while suppressing the echo component.
Inventors
- 👤 David Arthur Berkley
- 👤 Olga Mary Mracek Mitchell
- 👤 John Robinson Pierce
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 12:10
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04B3/21
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
117 words
For a voice communications system containing imperfectly isolated transmit and receive paths, apparatus for reducing echo caused by leakage therebetween, comprising: means for dividing the transmit path signal into plural contiguous subbands, means for producing, from an incoming voice signal in the receive path, a replica of the echo of said voice signal occurring in each of said transmit path subbands, means for continuously detecting the peak level of each said echo replica, means for center-clipping the signal in each transmit path subband a varying amount in response to the concurrent said peak level value, sufficient to just overcome said echo in the respective subband, and means for combining the outputs of each center-clipping means for transmission.
Claim 2
Dependent Claim
117 words
For a voice communications system containing imperfectly isolated transmit and receive paths, apparatus for reducing echo caused by leakage therebetween, comprising: means for dividing the transmit path signal into plural contiguous subbands, means for producing, from an incoming voice signal in the receive path, a replica of the echo of said voice signal occurring in each of said transmit path subbands, means for continuously detecting the peak level of each said echo replica, means for center-clipping the signal in each transmit path subband a varying amount in response to the concurrent said peak level value, sufficient to just overcome said echo in the respective subband, and means for combining the outputs of each center-clipping means for transmission.
Claim 3
Dependent Claim
89 words
Apparatus pursuant to claim 1, wherein said dividing means comprises a first set of contiguous band filters; and wherein said echo replica-producing means comprises a second set of contiguous band filters spanning the same subbands as said first set and being connected across said receive path, an attenuator connected to the output of each filter in said second set, and means for setting each attenuation level to obtain an output from each said attenuator having an amplitude comparable to said echo signal occurring in the corresponding transmit path subband.
Claim 4
Dependent Claim
11 words
Apparatus pursuant to claim 2, wherein said attenuation levels are fixed.
Claim 5
Dependent Claim
79 words
Apparatus pursuant to claim 2, further comprising means for varying said attenuation levels, comprising: a white noise generator connected to said receive path, means responsive to a selected initiating circuit condition for energizing said generator, means for sensing the resulting echo signal level exiting from said center-clippers in each of said transmit path subbands, and means responsive to each said sensed level for adjusting the corresponding attenuator until no echo signal is sensed, and thereafter, for deenergizing said generator.
Claim 6
Dependent Claim
30 words
Apparatus pursuant to claim 2, wherein said center-clipping means includes means for returning said clipping levels to zero a prescribed time after disappearance of an echo signal in that subband.
Claim 7
Dependent Claim
21 words
Apparatus pursuant to claim 2, wherein said center-clipping means includes means for returning said clipping levels to a selected minimum value.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-17 | 1976-04-17 | 1976-10-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-17 | 1980-04-17 | 1980-10-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-17 | 1984-04-17 | 1984-10-17 | $7700.00 | Window Closed / Lapsed |