Hands free telecommunication apparatus and method
First Claim
1. A hands free communication terminal apparatus including a receive path having a loudspeaker, for coupling signals from a far end party via a transmission medium to the loudspeaker, and a transmit path having a microphone, for coupling signals from a near end user via the microphone and the transmission medium to the far end part, the hands free communication terminal apparatus comprising:
- a voice switch including a receive variable attenuator being connected in series with the receive path and a transmit variable attenuator being connected in series with the transmit path, the variable attenuators being operable to effect switchable transmit and receive modes of operation;
a first echo canceller being connected between the transmit and receive paths and being adaptive to respond to signals in the receive path for reducing amplitudes of corresponding delayed signals from the microphone in the transmit path; and
a controller being responsive to signals in the transmit and receive paths, for adapting the operation of the echo canceller, and being responsive to signals from the echo canceller in the transmit path and to signals in the receive path, for switching the voice switch between receive and transmit modes of operation.
4 Assignments
0 Petitions
Accused Products
Abstract
In a hands free communications terminal apparatus, a loudspeaker and a microphone are permitted to be simultaneously active. A controller monitors signals in transmit and receive paths to direct operations of transversal filters to provide two echo canceller functions, one for the microphone and one for a telephone line so that most unwanted echo and feedback is removed, to prevent the howling and squealing sounds that commonly occur when the loudspeaker and the microphone are both active. Remaining echoes are removed by voice switching of loss between transmit and receive paths, wherein the amount of loss is determined in response to characteristics of the telephone line and the operating environment of the terminal apparatus.
94 Citations
15 Claims
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1. A hands free communication terminal apparatus including a receive path having a loudspeaker, for coupling signals from a far end party via a transmission medium to the loudspeaker, and a transmit path having a microphone, for coupling signals from a near end user via the microphone and the transmission medium to the far end part, the hands free communication terminal apparatus comprising:
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a voice switch including a receive variable attenuator being connected in series with the receive path and a transmit variable attenuator being connected in series with the transmit path, the variable attenuators being operable to effect switchable transmit and receive modes of operation; a first echo canceller being connected between the transmit and receive paths and being adaptive to respond to signals in the receive path for reducing amplitudes of corresponding delayed signals from the microphone in the transmit path; and a controller being responsive to signals in the transmit and receive paths, for adapting the operation of the echo canceller, and being responsive to signals from the echo canceller in the transmit path and to signals in the receive path, for switching the voice switch between receive and transmit modes of operation. - View Dependent Claims (2, 3, 4, 5, 6, 15)
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7. A hands free telecommunications instrument, for use with a transmission medium, comprising:
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a receive path including an output terminal, the receive path being for carrying binary information signals received from the transmission medium to a loudspeaker via the output terminal; a transmit path including an input terminal, the transmit path being for carrying binary information signals transmitted from a microphone, via the input terminal, to the transmission medium; a voice switch means including transmit and receive variable attenuators within the transmit and receive paths respectively, for passing the received and transmitted information signals with variable attenuation; a controller being responsive to relative strengths of the received and transmitted information signals for controlling the transmit and receive variable attenuators to impede the information signals traversing either one of the variable attenuators, with a set amount of attenuation; a summing means including first and second inputs and an output, and being connected in series between the input of the transmit path and the transmit variable attenuator via the first input and the output respectively; an transversal filter having an input connected to the receive path and an output connected to the second input of the summing means, and in combination with the summing means being operable as directed by the controller and in response to the binary information signals in the receive path, to reduce signals in the transmit path resulting from a substantially direct acoustical coupling between the loudspeaker and the microphone; the controller also being operable for varying the set amount of attenuation in direct proportion to a subsonic average of signals arriving at the microphone from the loudspeaker via a substantially indirect acoustical coupling being of greater length and greater delay than that of the substantially direct acoustical coupling. - View Dependent Claims (8, 9)
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10. A method for operating a hands free communication terminal apparatus which has a receive path with a loudspeaker, for coupling signals from a far end party via a transmission medium to the loudspeaker, and a transmit path with a microphone for coupling signals from a near end user via the microphone to the transmission medium, the method comprising the steps of:
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echo cancelling signals from the microphone in the transmit path in response to signals in the receive path for reducing delayed appearances of said signals in the transmit path to produce echo cancelled signals in the transmit path; in response to signals in the transmit and receive paths, adapting the step of the echo cancelling whereby reduction of said delayed appearances of said signals in the transmit path is limited to signal appearances of short delay and whereby the reduction is sufficient to avoid singing; and in response to signals from the echo canceller in the transmit path, and to signals in the receive path, switching a receive variable attenuator and a transmit variable attenuator in a complementary manner between receive and transmit modes of operation. - View Dependent Claims (11, 12)
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13. A method for audible hands free telecommunications via a transmission medium and a telephone instrument which includes a loudspeaker and a microphone, wherein sounds at the microphone include sounds from the loudspeaker acoustically coupled thereto via first paths with a time delay of up to about twenty milliseconds, and sounds from the loudspeaker acoustically coupled thereto via second paths with a time delay of more than about twenty milliseconds, the method comprising the steps of:
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(a) receiving receive signals at the telephone instrument from the transmission medium; (b) in response to the receive signals, producing audible sounds therefrom, via the loudspeaker; (c) in response to audible sounds in the room, generating transmit signals, via the microphone; (d) transmitting the transmit signals from the telephone instrument to the transmission medium; (e) before transmitting in step (d), echo cancelling the transmit signals with the receive signals; (f) in response to respective energies of the receive and transmit signals performing the respective steps (a) of receiving and (d) of transmitting with complementary losses being switched therebetween, a value of said complementary losses being less than that required to prevent singing were it not for the step (e) of echo cancelling. - View Dependent Claims (14)
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Specification