EP0106640A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Noise control circuit
Assignee: British Telecommunications PLC
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Filing: 1983-10-06
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Granted: —
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Expires: 2003-10-06
Abstract
Abstract Residual noise control is provided on telecommunications links which are at least partly 4-wire, by means of a variable threshold centre clipper 30 applied to the output of an echo canceller 100. The threshold of the centre clipper 30 is varied in accordance with the magnitude of an echo estimate 21 generated by the echo canceller 100. In order to prevent mutilation of near end speech the clipper is disabled when such speech is detected. However, the echo canceller 100, remains in circuit to allow control of echo even during doubletalk. The clippers threshold may be controlled in response to the instantaneous modulus of the echo estimate. Alternatively, the echo estimate may be fed to a modulator 60 and filter 55 to provide a short term filtered version of the echo estimate which allows control of other components of residual noise.
Inventors
- 👤 Nicholas John Arnold Forse
- 👤 Robert Denis Johnson
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 17:01
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04B3/23; H04B3/234
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
57 words
A noise control circuit for use in a communications link having separate receive (2) and return (3) channels comprising an echo canceller (100) and an adaptive clipper (30 or 65) characterised in that an echo estimate (21) produced by said echo canceller (100) is used to control, via signal processing means, the threshold of said adaptive clipper.
Claim 2
Dependent Claim
57 words
A noise control circuit for use in a communications link having separate receive (2) and return (3) channels comprising an echo canceller (100) and an adaptive clipper (30 or 65) characterised in that an echo estimate (21) produced by said echo canceller (100) is used to control, via signal processing means, the threshold of said adaptive clipper.
Claim 3
Dependent Claim
18 words
A noise control circuit as claimed in claim 1 wherein said signal processing means includes a filter (55).
Claim 4
Dependent Claim
32 words
A noise centre clipper as claimed in claim 1 or claim 2 wherein said signal processing means produce short term samples of said echo estimate (21) for use in controlling said threshold.
Claim 5
Dependent Claim
30 words
A noise control circuit as claimed in claim 3 wherein said signal processing means operate to select the largest of said samples from amongst a number, N, of previous samples.
Claim 6
Dependent Claim
23 words
A noise control circuit as claimed in claim 4 wherein said largest sample is used to control the threshold of said adaptive clipper.
Claim 7
Dependent Claim
19 words
A noise control circuit as claimed in claim 4 or claim 5 wherein N is between 10 and 100..
Claim 8
Dependent Claim
58 words
A noise control circuit as claimed in any one of the preceding claims wherein said echo canceller (100) includes an echo subtractor (45) by means of which said echo estimate (21) is utilised to remove echo from said return channel (3), the output from said echo subtractor being used as a feedback signal to improve the echo estimation.
Claim 9
Dependent Claim
34 words
A noise control circuit as claimed in any one of the preceding claims in which the echo canceller (100) together with its associated echo subtractor (45) contributes a loss of no more than 20dB.
Claim 10
Dependent Claim
22 words
A noise control circuit as claimed in any one of the preceding claims, wherein said 4-wire telecommunications link is a digital link.
Claim 11
Dependent Claim
31 words
A telephone operator's telephone equipment wherein a noise control circuit as claimed in any of the above claims is used to control the amount of sidetone fed to an operator's earpiece.
Claim 12
Dependent Claim
31 words
A telephone operator's telephone equipment as claimed in claim 10 wherein an additional signal path is provided to allow a desired amount of sidetone to be fed to an operator's earpiece.
Claim 13
Dependent Claim
25 words
A noise control circuit as claimed in any one of the above claims positioned at a junction of a national and an international telecommunications circuit.
Claim 14
Dependent Claim
24 words
A noise control circuit as claimed in any one of the above claims positioned at a junction between a satellite and a land circuit.
Claim 15
Dependent Claim
43 words
A loudspeaking telephone (140) which incorporates an echo canceller (210 or 240) and an associated adaptive clipper (270 or 260) wherein an echo estimate produced by said echo canceller is used to control, via signal processing means, the threshold of said adaptive clipper.
Claim 16
Dependent Claim
43 words
A loudspeaking telephone (140) which incorporates an echo canceller (210 or 240) and an associated adaptive clipper (270 or 260) wherein an echo estimate produced by said echo canceller is used to control, via signal processing means, the threshold of said adaptive clipper.
Claim 17
Dependent Claim
37 words
A loudspeaking telephone as claimed in claim 14 wherein said echo canceller monitors the signal on the telephone's loudspeaker circuit (160), and said adaptive clipper is arranged to clip the signal on the telephone's microphone circuit (190).
References Cited (Backward Citations)
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