Minimization of transient noises in a voice signal

• US 7,725,315 B2
• Filed: 10/17/2005
• Issued: 05/25/2010
• 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: Hetherington, Phillip A., Paranjpe, Shreyas
• Primary Examiner(s): Dorvil; Richemond
• Assistant Examiner(s): He; Jialong
• Application Number:
  US11/252,160
• Publication Number:
  US 20060100868A1
• Time in Patent Office: 1,681 Days
• Field of Search: 704/226, 704/233
• US Class Current: 704/233
• 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 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 that converts a received signal into a digital signal;

a windowing function generator that divides the digital signal into a plurality of individual analysis windows;

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

a modeler that generates and stores model attributes of transient road noise, and that compares attributes of the short term spectra of the transformed analysis windows to the model attributes to determine whether a transient noise present in the received signal is a transient road noise, where the model attributes include the presence of two sound events separated by a period of time based on the speed at which a vehicle is traveling and a distance between front and rear wheels of the vehicle, and where the period of time between the two sound events is determined by an adaptive model.

2. The transient road noise detector of claim 1, further comprising an average transient road noise model generated from the plurality of individual analysis windows and wherein the model attributes comprise average transient road noise model attributes obtained from the average transient road noise model.

3. The transient road noise detector of claim 1 wherein the windowing function generator is a Hanning window function generator.

4. The transient road noise detector of claim 1 wherein the model attributes include temporal characteristics typical of transient road noises, and where the modeler identifies the transient noise as being transient road noise based on a similarity between attributes of the transient noise and the temporal characteristics typical of transient road noises.

5. The transient road noise detector of claim 1 wherein the model attributes include spectral characteristics typical of transient road noises, and where the modeler identifies the transient noise as being transient road noise based on a similarity between attributes of the short term spectra of the transformed analysis windows and the spectral characteristics typical of transient road noises.

6. The transient road noise detector of claim 1 wherein the model attributes include both temporal and spectral characteristics typical of transient road noises, and where the modeler identifies the transient noise as being transient road noise based on a similarity between attributes of the transient noise and the temporal and spectral characteristics typical of transient road noises.

7. The transient road noise detector of claim 6 wherein the model attributes include the presence of two sound events having substantially similar spectral characteristics separated by a relative short time period.

8. The transient road noise detector of claim 7 wherein the model attributes include spectral shape characteristics of the two sound events.

9. The transient road noise detector of claim 8 wherein a function is fitted to a selected portion of a signal in a time-frequency domain to evaluate spectro-temporal shape characteristics of the two sound events.

10. The transient road noise detector of claim 1 further comprising a residual attenuator for tracking a power spectrum of a signal, and when a large increase in signal power is detected, limiting a transmitted power in a low frequency range to a predetermined value based on a average spectral power of the signal in the low frequency range from an earlier period in time.

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

modeling characteristics of transient road noises, where the modeled characteristics of transient road noises include a sonic doublet of two sound events separated by an amount of time corresponding to a length of time between front tires of a vehicle traveling at a rate of speed striking an obstacle and rear tires of the vehicle striking the obstacle, and where the amount of time between the two sound events is determined by an adaptive model;

analyzing the signal to determine whether characteristics of the signal correspond to the modeled characteristics of transient road noises to determine whether a transient noise present in the signal is a transient road noise; and

passing the signal through a noise attenuator to substantially remove from the signal the characteristics of the signal that correspond to the modeled characteristics of transient road noises.

12. The method of claim 11 wherein the vehicle has a wheel base having a length, and wherein the length of the wheel base and the rate of speed at which the vehicle is traveling are known, the method further comprising calculating the amount of time between the two sound events corresponding to a transient road noise sonic doublet based on the length of the wheel base and the rate of speed at which the vehicle is traveling.

13. The method of claim 11 further comprising modeling a temporal separation between the two sound events comprising a sonic doublet characterizing a transient road noise.

14. The method of claim 11 wherein:

modeling comprises deriving an average transient road noise model from multiple modeled characteristics of the transient road noises; and

analyzing comprises determining whether the characteristics of the signal correspond to characteristics of the average transient road noise model.

15. The method of claim 11 wherein the modeled characteristics of transient road noises further include spectral shape attributes of the sound events comprising the sonic doublet associated with transient road noises.

16. The method of claim 15 wherein the spectral shape attributes of the sound events include a broadband event with peak energy levels concentrated at relatively lower frequencies.

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

a transient road noise detector that detects a presence of transient road noise in the signal; and

a transient road noise attenuator that substantially removes transient road noise detected in the signal;

wherein the transient road noise detector includes a model of transient road noise and wherein the transient road noise detector compares 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 determines that the attribute of the signal is in substantial agreement with the attribute of the model;

wherein the model includes a spectral component and a temporal component, and the temporal component comprises a first sound event and a second substantially similar sound event separated by a period of time;

wherein the period of time between the first sound event and the second sound event is based on a speed at which a vehicle is traveling and a distance between front and rear wheels of the vehicle; and

wherein the period of time between the first sound event and the second sound event is determined by an adaptive model.