STATIONARY-TONES INTERFERENCE CANCELLATION

• US 20080243497A1
• Filed: 03/28/2007
• Published: 10/02/2008
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Malvar, Henrique S., Tashev, Ivan
• Granted Patent: US 7,752,040 B2
• Time in Patent Office: Days
• US Class Current: 704/227
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 25/27 characterised by the analysis technique

Abstract

An “Interference Canceller” provides a computationally efficient real-time technique for removing stationary-tone interference from signals. Typical sources of stationary tone contamination of signals include noise from power wiring (i.e., 50/60 Hz or 400 Hz and their harmonics), frame or line frequencies from electronic devices, and noise from computer fans, hard disk drives, etc. In general, the Interference Canceller adaptively builds and updates a model of stationary tone interference in consecutive frames of an input signal. This adaptively updated model is then used to extrapolate and subtract noise from subsequent frames of the input signal to generate a “clean” output signal. This output signal exhibits significant attenuation of stationary tone interference without eliminating important portions of the underlying signal or distorting the underlying signal with artifacts such as musical noise or nonlinear distortions. The Interference Canceller is applicable for use either alone, or as pre-processor to conventional noise suppression.

Claims

1. A computer-readable medium having computer executable instructions for canceling approximately stationary noise from an input signal, said computer executable instructions comprising:

receiving an input signal including contamination by one or more noise sources;

processing consecutive partially overlapping frames of the input signal to produce corresponding blocks of frequency domain transform coefficients for each frame of the input signal;

for each block of transform coefficients, updating an estimated complex model of noise contaminating the input signal, said model including any of stationary and approximately stationary noise;

for each block of transform coefficients, estimating a complex plane rotation speed of frequency components comprising each block of transform coefficients;

for each block of transform coefficients, using the estimated complex model of noise in combination with the estimated rotation speed of the frequency components to extrapolate an estimate of the noise to a next sequential block of transform coefficients; and

subtracting the extrapolated estimate of the noise from each next sequential block of transform coefficients to generate a frequency domain representation of an output signal.

2. The computer-readable medium of claim 1 wherein the input signal further includes contamination by non-predictable noise, and further comprising performing a frequency-domain noise suppression operation on the frequency domain representation of the output signal to attenuate the non-predictable noise.

3. The computer-readable medium of claim 1 further comprising transforming the frequency domain representation of the output signal to reconstruct a time domain version of the output signal, said time domain version of the output signal representing a version of the input signal from which an estimate of the approximately stationary noise has been cancelled.

4. The computer-readable medium of claim 3 further comprising providing a real-time playback of the output signal.

5. The computer-readable medium of claim 1 wherein the input signal is a real-time speech signal.

6. The computer-readable medium of claim 5 further comprising computing a probability of speech absence for each block of transform coefficients, and wherein the probability of speech absence is used in computing the estimated complex model of noise and the estimated complex plane rotation speeds.

7. The computer-readable medium of claim 5 further comprising encoding the frequency domain representation of the output signal using a transform-domain encoder.

8. A method for canceling noise from a signal, comprising using a computing device to:

receive a frequency-domain representation of a noisy input signal comprising consecutive blocks of transform coefficients corresponding to overlapping frames of the noisy input signal;

estimating a complex plane rotation speed of frequency components comprising each block of transform coefficients;

evaluating each block of transform coefficients to generate an estimated complex noise model for modeling predictable noise, including any of stationary and approximately stationary noise, in the noisy input signal;

for each block of transform coefficients, using the estimated complex noise model in combination with the estimated rotation speeds to extrapolate an estimate of the predictable noise to a next sequential block of transform coefficients; and

from each next sequential block of transform coefficients, subtracting the extrapolated estimate of noise to generate a frequency domain representation of an output signal.

9. The method of claim 8 further comprising performing a frequency-domain noise suppression operation on the frequency domain representation of the output signal to attenuate non-predictable noise in the noisy input signal.

10. The method of claim 8 wherein the input signal is a real-time speech signal.

11. The method of claim 10 further comprising transforming the frequency domain representation of the output signal to reconstruct a time domain version of the output signal.

12. The method of claim 11 further comprising providing a real-time playback of the time-domain version of the output signal.

13. The method of claim 10 further comprising computing a probability of speech absence for each block of transform coefficients, and wherein the probability of speech absence is used in computing the estimated complex noise model and the estimated complex plane rotation speeds.

14. A system for providing real-time noise cancellation in a speech signal, comprising using a computing device to perform steps for:

receive overlapping frames of a real-time time domain input of a noisy speech signal;

as each frame of the noisy input signal is received, transform each frame into a corresponding block of transform coefficients;

evaluating each block of transform coefficients to generate an estimated noise model for modeling any of stationary and approximately stationary noise in the noisy input signal;

estimating complex plane rotation speeds of frequency components comprising each block of transform coefficients from each current block of transform coefficients towards corresponding frequency components in each next block of transform coefficients;

for each block of transform coefficients, using the estimated noise model in combination with the estimated rotation speeds to extrapolate an estimate of the stationary and approximately stationary noise to a next sequential block of transform coefficients;

from each next sequential block of transform coefficients, subtracting the extrapolated estimate of noise to generate a frequency domain representation of an output signal; and

transforming each block of coefficients of the frequency domain representation of the output signal to the time domain to reconstruct a real-time time domain speech output signal.

15. The system of claim 14 further comprising performing a frequency-domain noise suppression operation on the frequency domain representation of the output signal prior to transforming the signal to the time domain to attenuate non-predictable noise in the noisy speech signal.

16. The system of claim 14 further comprising providing a real-time playback of the time domain speech output signal.

17. The system of claim 14 further comprising encoding each block of transform coefficients of the frequency domain representation of the output signal to compress the frequency domain representation of the output signal for transmission across a network.

18. The system of claim 14 further comprising computing a probability of speech absence for each block of transform coefficients of the noisy input signal, and wherein the probability of speech absence is used in computing the estimated noise model and the estimated complex plane rotation speeds.

19. The system of claim 18 wherein computing a probability of speech absence for each block of transform coefficients comprises processing each block of transform coefficients using a voice activity detector.

20. The system of claim 14 further comprising storing the time domain speech output signal on a computer readable medium.