US4591670A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Echo canceller and echo suppressor for frequency divisional attenuation of acoustic echoes
Assignee: NEC Corp
•
Filing: 1983-09-15
•
Granted: 1986-05-27
•
Expires: 2003-09-15
Abstract
Abstract An echo cancelling circuit is composed of digital circuits. An echo canceller is supplied with lower send-in and receive-in components derived from a send-in and a receive-in digital signal, respectively, in a lower frequency band below a predetermined frequency. The echo canceller produces a lower digital signal component which is free from a lower echo signal component. The echo canceller furthermore produces a control signal indicative of presence and absence of a lower voice signal component in the lower send-in component. Controlled by the control signal and supplied with a higher send-in component of a frequency band higher than the predetermined frequency, an adjustable attenuator produces a higher digital signal component in which a higher echo signal component is suppressed with no attenuation and either a constant or an adjustable positive attenuation given to the higher send-in component when the control signal indicates presence and absence of the lower voice signal component, respectively. The lower and the higher digital signal components are combined into a send-out signal exempted from the echo signal, which may or may not comprise a reverberation signal introduced into the send-in digital signal by audible sound reproduced from a voice signal carried by the receive-in digital signal.
Inventors
- 👤 Yasuo Itoh
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 20:05
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
287 words
An echo cancelling circuit responsive to a receive-in digital signal for feeding a receive-out signal to a receiver and responsive to a send-in digital signal delivered from a transmitter for producing a send-out signal, said echo cancelling circuit being furthermore for exempting said send-out signal from an echo signal which results from said receive-in digital signal, said receive-in digital signal comprising voice information which makes said receiver reproduce audible sound, said send-in digital signal comprising an acoustic signal when said transmitter is spoken to, said echo cancelling circuit comprising: a first send-in digital filter responsive to said send-in digital signal for producing a first send-in component, said first send-in component comprising an acoustic signal component when said send-in digital signal comprises said acoustic signal; a second send-in digital filter responsive to said send-in digital signal for producing a second send-in component; a receive-in digital filter responsive to said receive-in digital signal for producing a first receive-in component, said first receive-in component comprising a voice information component when said receive-in digital signal comprises said voice information; echo cancelling means responsive to said first send-in component and said first receive-in component for self-adaptively cancelling said echo signal to produce a first local digital signal component which is exempted substantially from said echo signal, said echo cancelling means being furthermore responsive to at least one of said first send-in component and said first receive-in component for producing a control signal indicative of presence and absence of said acoustic signal component; adjustable attenuating means responsive to said control signal for producing a second local digital signal component by attenuating said second send-in component; and combining means for combining said first and said second local digital signal components into said send-out signal.
Claim 2
Dependent Claim
287 words
An echo cancelling circuit responsive to a receive-in digital signal for feeding a receive-out signal to a receiver and responsive to a send-in digital signal delivered from a transmitter for producing a send-out signal, said echo cancelling circuit being furthermore for exempting said send-out signal from an echo signal which results from said receive-in digital signal, said receive-in digital signal comprising voice information which makes said receiver reproduce audible sound, said send-in digital signal comprising an acoustic signal when said transmitter is spoken to, said echo cancelling circuit comprising: a first send-in digital filter responsive to said send-in digital signal for producing a first send-in component, said first send-in component comprising an acoustic signal component when said send-in digital signal comprises said acoustic signal; a second send-in digital filter responsive to said send-in digital signal for producing a second send-in component; a receive-in digital filter responsive to said receive-in digital signal for producing a first receive-in component, said first receive-in component comprising a voice information component when said receive-in digital signal comprises said voice information; echo cancelling means responsive to said first send-in component and said first receive-in component for self-adaptively cancelling said echo signal to produce a first local digital signal component which is exempted substantially from said echo signal, said echo cancelling means being furthermore responsive to at least one of said first send-in component and said first receive-in component for producing a control signal indicative of presence and absence of said acoustic signal component; adjustable attenuating means responsive to said control signal for producing a second local digital signal component by attenuating said second send-in component; and combining means for combining said first and said second local digital signal components into said send-out signal.
Claim 3
Dependent Claim
56 words
An echo cancelling circuit as claimed in claim 1, wherein said adjustable attenuating means is controlled by said control signal to give a zero attenuation or a finite attenuation to said second send-in component to produce said second local digital signal component when said control signal indicates presence or absence of said acoustic signal component, respectively.
Claim 4
Dependent Claim
116 words
An echo cancelling circuit as claimed in claim 2, wherein said adjustable attenuating means comprises: a switch responsive to said control signal for suppling the output of said adjustable attenuating means with said second send-in component as said second local digital signal when said control signal indicates the presence of said acoustic signal component and for supplying said second send-in component to a digital attenuator when said control signal indicates the absence of said acoustic signal component; and a digital attenuator receiving said second send-in component and giving said finite attenuation to said second send-in component to produce said second local digital signal component when said control signal indicates the absence of said acoustic signal component.
Claim 5
Dependent Claim
15 words
An echo cancelling circuit as claimed in claim 2, wherein said finite attenuation is adjustable.
Claim 6
Dependent Claim
68 words
An echo cancelling circuit as claimed in claim 1, wherein said echo cancelling means comprises: control means responsive to at least one of said first send-in component and said first receive-in component for producing said control signal; and an echo canceller responsive to said first send-in component, said first receive-in component, and said control signal for self-adaptively cancelling said echo signal to produce said first digital signal component.
Claim 7
Dependent Claim
113 words
An echo cancelling circuit as claimed in claim 5, each of said first send-in component and said first receive-in component being sampled with a predetermined sampling period, wherein said echo canceller comprises: a transversal filter for processing said first receive-in component by digital tap gains to produce a digital simulation signal which substantially simulates said echo signal; a digital subtractor for substracting said simulation signal from said first send-in component to produce a digital difference signal; and tap gain adjusting means responsive to said first receive-in component, said difference signal, and said control signal for self-adaptively adjusting said digital tap gains so that said difference signal becomes said first local digital signal component.
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) | 1989-05-26 | 1989-11-25 | 1990-05-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-05-26 | 1993-11-25 | 1994-05-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-05-26 | 1997-11-25 | 1998-05-27 | $7700.00 | Window Closed / Lapsed |