Minimization of transient noises in a voice signal

• US 20060100868A1
• Filed: 10/17/2005
• Published: 05/11/2006
• Est. Priority Date: 02/21/2003
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: QNX Software Systems Company (Blackberry Limited)
• Inventors: Paranjpe, Shreyas A., Hetherington, Phillip A.
• Granted Patent: US 7,725,315 B2
• Time in Patent Office: Days
• US Class Current: 704/226
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain

Abstract

A voice enhancement system is provided for improving the perceptual quality of a processed voice signal. The system improves the perceptual quality of a received voice signal by removing unwanted noise from a voice signal recorded by a microphone or from some other source. Specifically, the system removes sounds that occur within the environment of the signal source but which are unrelated to speech. The system is especially well adapted for removing transient road noises from speech signals recorded in moving vehicles. Transient road noises include common temporal and spectral characteristics that can be modeled. A transient road noise detector employs such models to detect the presence of transient road noises in a voice signal. If transient road noises are found to be present, a transient road noise attenuator is provided to remove them from the signal.

Claims

1. A system for suppressing transient road noises from a signal comprising

a transient road noise detector adapted to detect the presence of transient road noise in the signal;

and

a transient road noise attenuator for substantially removing road transient noise detected in the received signal.

2. The system of claim 1 wherein the transient road noise detector includes a model of transient road noise and wherein the transient road noise detector is adapted to compare an attribute of the signal with an attribute of the model, the transient road noise detector detecting the presence of a transient road noise in the signal when the transient road noise detector determining that an attribute of the signal is in substantial agreement with an attribute of the model.

3. The system of claim 2 wherein the model includes a spectral component and a temporal component.

4. The system of claim 3 wherein the temporal component comprises a first sound event and a second substantially similar sound event separated by a period of time.

5. The system of claim 4 wherein the period of time between the first sound event and the second sound event is based on the speed at which the vehicle is traveling and a distance between front and rear wheels of the vehicle.

6. The system of claim 5 wherein the period of time between the first sound event and the second sound event is based on a calculation of the actual speed at which the vehicle is traveling and the length of the vehicle'"'"'s wheel base.

7. The system of claim 5 wherein the period of time between the first sound event and the second sound event is determined by an adaptive model.

8. The system of claim 3 wherein the spectral component comprises one or more attributes of a spectral shape of a sound event associated with a transient road noise.

9. The system of claim 8 wherein the attributes of the spectral shape of a sound event associated with a transient road noise include a broadband frequency response with peak intensity at relatively lower frequency ranges.

10. A transient road noise detector for detecting the presence of transient road noise in a signal, the transient road noise detector comprising:

an analog to digital converter for converting a received signal into a digital signal;

a windowing function generator for dividing the signal into a plurality of individual analysis windows;

a transform module for transforming the individual analysis windows from time domain signals to frequency domain short term spectra; and

a modeler for at least one of generating and storing model attributes of transient road noise, and comparing attributes of the short term spectra of the transformed analysis windows to the model attributes to determine whether a transient road noise is present in the received signal.

11. The transient road noise detector of claim 10, wherein the analog to digital converter converts the received signal into a pulse code modulated (PCM) signal.

12. The transient road noise detector of claim 10 wherein the windowing function generator is a Hanning window function generator.

13. The transient road noise detector of claim 10 wherein the transform module performs a fast Fourier transform on the individual analysis windows.

14. The transient road noise detector of claim 10 wherein the model attributes include temporal characteristics typical of transient road noises.

15. The transient road noise detector of claim 10 wherein the model attributes include spectral characteristics typical of transient road noises.

16. The transient road noise detector of claim 10 wherein the model attributes include both temporal and spectral characteristics typical of transient road noises.

17. The transient road noise detector of claim 16 wherein the model attributes include the presence of two sound events having substantially similar spectral characteristics separated by a relative short time period.

18. The transient road noise detector of claim 17 wherein the model attributes include spectral shape characteristics of the two sound events.

19. The transient road noise detector of claim 18 wherein a function is fitted to a selected portion of the signal in the time-frequency domain to evaluate the spectro-temporal shape characteristics of the two sound events.

20. The transient road noise detector of claim 10 further comprising a residual attenuator for tracking the power spectrum of the signal and when a large increase in signal power is detected limiting the transmitted power in a low frequency range to a predetermined value based on the average spectral power of the signal in the low frequency range from an earlier period in time.

21. A method of removing transient road noises from a signal comprising:

modeling characteristics of transient road noises;

analyzing the signal to determine whether characteristics of the signal correspond to the modeled characteristics of transient road noises; and

substantially removing from the signal the characteristics of the received signal that correspond to the modeled characteristics of transient road noises.

22. The method of claim 21 wherein modeled characteristics of transient road noises include sonic doublets of two sound events separated in time.

23. The method of claim 22 wherein the two sound events comprising a sonic doublet are separated by an amount of time corresponding to a length of time between the front tires of a vehicle traveling at a rate of speed striking an obstacle and the rear tires of the vehicle striking the obstacle.

24. The method of claim 23 wherein the vehicle has a wheel base having a length, and wherein the length of the wheel and the rate of speed at which the vehicle is traveling are known, the method further comprising calculating the time separation between the two sound events corresponding to a transient road noise sonic doublet based of the length of the wheelbase and the rate of speed at which the vehicle is traveling.

25. The method of claim 22 further comprising modeling the temporal separation between the two sound events comprising a sonic doublet characterizing a transient road noise.

26. The method of claim 25 wherein a leaky integrator is employed to model the temporal separation of transient road noise sonic doublets.

27. The method of claim 22 wherein the modeled characteristics of transient road noises further includes spectral shape attributes of the sound events comprising the sonic doublets associated with transient road noises.

28. The method of claim 27 wherein the spectral shape attributes of the sound events include a broadband event with peak energy levels concentrated at relatively lower frequencies.