Stephen D Mcgrath

US Patent:

6351731, Feb 26, 2002

Filed:

Aug 10, 1999

Appl. No.:

09/371306

Inventors:

David V. Anderson - Alpharetta GA
Stephen McGrath - Atlanta GA
Kwan Truong - Lilburn GA

Assignee:

Polycom, Inc. - Milpitas CA

International Classification:

G10L 1102

US Classification:

704233, 704225, 704226

Abstract:

An adaptive filter is provided featuring a speech spectrum estimator receiving as input an estimated spectral magnitude signal for a time frame of the input signal and generating an estimated speech spectral magnitude signal representing estimated spectral magnitude values for speech in a time frame. A spectral gain generator receives as input the estimated spectral magnitude signal and the estimated speech spectral magnitude signal and generates as output an initial spectral gain signal that yields an estimate of speech spectrum in a time frame of the input signal when the initial spectral gain signal is applied to the spectral signal. A spectral gain modifier receives as input the initial spectral gain signal and generates a modified gain signal by limiting a rate of change of the initial spectral gain signal with respect to the spectral gain over a number of previous time frames. The modified gain signal is then applied to the spectral signal, which is then converted to its time domain equivalent. The value of the noise multiplier is larger when a time frame of the input signal contains more noise than speech and is smaller when a time frame of the input signal contains more speech than noise.

US Patent:

6453285, Sep 17, 2002

Filed:

Aug 10, 1999

Appl. No.:

09/371748

Inventors:

David V. Anderson - Alpharetta GA
Stephen McGrath - Atlanta GA
Kwan Truong - Lilburn GA

Assignee:

Polycom, Inc. - Milpitas CA

International Classification:

G10L 1102

US Classification:

704210, 704226, 381 943

Abstract:

A system and method for removing noise from a signal containing speech (or a related, information carrying signal) and noise. A speech or voice activity detector (VAD) is provided for detecting whether speech signals are present in individual time frames of an input signal. The VAD comprises a speech detector that receives as input the input signal and examines the input signal in order to generate a plurality of statistics that represent characteristics indicative of the presence or absence of speech in a time frame of the input signal, and generates an output based on the plurality of statistics representing a likelihood of speech presence in a current time frame; and a state machine coupled to the speech detector and having a plurality of states. The state machine receives as input the output of the speech detector and transitions between the plurality of states based on a state at a previous time frame and the output of the speech detector for the current time frame. The state machine generates as output a speech activity status signal based on the state of the state machine, which provides a measure of the likelihood of speech being present during the current time frame.