Telephone set with background noise suppression function

• US 5,748,725 A
• Filed: 12/20/1994
• Issued: 05/05/1998
• Est. Priority Date: 12/29/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kubo, Masato
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US08/359,516
• Time in Patent Office: 1,232 Days
• Field of Search: 379/387, 379/390, 379/395, 379/402, 379/406, 379/407, 379/410, 379/411, 379/419, 379/433, 381/83, 381/92, 381/93, 381/94, 381/107, 381/104, 381/71
• US Class Current: 379/392.01
• CPC Class Codes: G10L 2021/02165 Two microphones, one receiving mainly the noise signal and the other one mainly the speech signal
• CPC Class Codes: G10L 21/0216 characterised by the method used for estimating noise
• CPC Class Codes: H04M 1/19 Arrangements of transmitters, receivers, or complete sets to prevent eavesdropping, to attenuate local noise or to prevent undesired transmission; Mouthpieces or receivers specially adapted therefor circuit arrangements for preventing eavesdropping H04M1/68; telephone cabinets E04H1/14
• CPC Class Codes: H04R 2410/05 Noise reduction with a separate noise microphone
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A telephone set is provided with a first microphone at the position close to a speaker and a signal including remaining noise is outputted from the first microphone. Background noise is outputted from a second microphone. A noise elimination circuit estimates background noise reaching the ear of a receiver based on the background noise signal, the signal including the remaining noise, and a received voice signal from a transmitter. Also, the noise elimination circuit subtracts the estimated background noise from the received voice signal to supply the resultant signal to the speaker.

Claims

1. A telephone set for suppressing background noise comprising:

a speaker for outputting a first voice signal;

a first microphone provided in the vicinity of said speaker, for generating a first voice band signal;

a second microphone for generating a second voice band signal including said background noise;

said noise elimination circuit comprising;

a level detector for comparing said received voice signal with a predetermined threshold value to output a control signal indicative of whether said received voice signal is equal to or higher than the predetermined threshold level;

a first adaptive filter for producing a third voice band signal based on said received voice signal and first tap coefficients and for updating said first tap coefficients based on said first voice band signal and an error signal when said control signal indicates that said received voice signal is higher than the threshold value;

a first subtracter for subtracting said third voice band signal from said first voice band signal to produce said error signal;

a second adaptive filter for producing said estimated background noise based on said second voice band signal and second tap coefficients and for updating said second tap coefficients when said control signal indicates that said received voice signal is lower than said threshold value; and

a second subtracter for subtracting said estimated background noise from said received voice signal to produce said first voice signal.

2. The telephone set as claimed in claim 1, wherein said first microphone is provided on a concentric axis of said receiver or speaker.

3. The telephone set as claimed in claim 2, wherein said second microphone is a transmission microphone.