Method of estimating noise levels in a communication system

1. A method of estimating noise level in data including voice information and noise, the method comprising:

receiving the data as a sequence of input values, the data provided in a frequency domain signal comprising frequency bands;

adding a bias value to at least two of the input values of the sequence, the bias values based, at least in part, on a corresponding frequency band;

transforming the data provided in the frequency domain signal comprising frequency bands by applying a first non linear mapping to the input values and the corresponding bias values, a derivative function of the first non linear mapping decreasing in magnitude as the input values increase in magnitude;

smoothing the transformed data, the smoothing being performed by a filter block comprising two inputs, one of the two inputs receiving the transformed data and another of the two inputs receiving speech indicator data from a speech detector;

transforming the smoothed transformed data by applying a second non linear mapping to the smoothed transformed data and the corresponding bias values, the second non linear mapping being opposite to the first non linear mapping;

determining an estimate of the noise level in the data based, at least in part, on the transforming the smoothed transformed data; and

using the determined estimate of the noise level in the data to produce a noise corrected signal.

2. A method as claimed in claim 1 wherein the smoothing comprises smoothing the transformed data using a low pass filter.

3. A method as claimed in claim 1 wherein the smoothing comprises smoothing the transformed data using time averaging.

4. A method as claimed in claim 1 wherein the smoothing comprises smoothing the transformed data using a smoothing coefficient.

5. A method as claimed in claim 4 further comprising detecting an indication of a presence of voice information in the data and increasing the smoothing.

6. A method as claimed in claim 5 wherein the smoothing is constant during the detecting the indication of the presence of the voice information.

7. A method as claimed in claim 5 wherein the increasing the smoothing comprises increasing the smoothing coefficient.

8. A method as claimed in claim 7 wherein the increasing the smoothing coefficient comprises increasing the smoothing coefficient to a value of 1.

9. A method as claimed in claim 4 further comprising:

applying the smoothing coefficient for each frequency band of the frequency domain signal,

detecting an indication of voice presence for each frequency band of the frequency domain signal; and

increasing the smoothing coefficient applied to a particular frequency band of the frequency domain signal if an indication of voice presence is detected for the particular frequency band.

10. A method as claimed in claim 1 wherein the first non linear mapping comprises a logarithmic mapping.

11. A method as claimed in claim 10 wherein the second non linear mapping comprises an exponential mapping.

12. A method as claimed in claim 1 wherein the first non linear mapping and the second non linear mapping maps the data to a multiplicative inverse of the data.

13. A method as claimed in claim 1 wherein transforming the data provided in the frequency domain signal comprising frequency bands by applying the first non linear mapping, smoothing the transformed data, and transforming the smoothed transformed data by applying the second non linear mapping are represented by an equation comprising:

y

⁡

(

n

)

=

1

/

(

α

y

⁡

(

n

-

1

)

+

1

-

α

x

⁡

(

n

)

)

where x(n) comprises the input values of the sequence, where y(n) comprises noise estimate values, and where a comprises a smoothing coefficient.

14. A method as claimed in claim 1 further comprising, prior to transforming the data, adding different bias values to at least some of the input values based on a corresponding frequency band.

15. A method as claimed in claim 1 , wherein applying the first non linear mapping to the input values comprising mapping each of the input values to a respective arc tangent, and wherein applying the second non linear mapping to the smoothed transformed data comprises mapping the tangent of the smoothed transformed data.

16. A system, comprising:

one or more processors; and

memory, communicatively coupled to the one or more processors, storing one or more components configured to implement operations comprising:

receiving data as a sequence of input values, the data provided in a frequency domain signal comprising frequency bands and including voice information and noise;

adding a bias value to at least two of the input values of the sequence, the bias values based, at least in part, on a corresponding frequency band;

transforming the data provided in the frequency domain signal comprising frequency bands by applying a first non linear mapping to the input values and the corresponding bias values, a derivative function of the first non linear mapping decreasing in magnitude as the input values increase in magnitude;

smoothing the transformed data, the smoothing being performed by a filter block comprising two inputs, one of the two inputs receiving the transformed data and another of the two inputs receiving speech indicator data from a speech detector;

transforming the smoothed transformed data by applying a second non linear mapping to the smoothed transformed data and the corresponding bias values, the second non linear mapping being opposite to the first non linear mapping;

determining an estimate of a noise level in the data based, at least in part, on the transforming the smoothed transformed data; and

using the determined estimate of the noise level in the data to produce a noise corrected signal.

17. A system as claimed in claim 16 wherein the smoothing comprises smoothing the transformed data using time averaging.

18. A system as claimed in claim 16 wherein the smoothing comprises smoothing the transformed data using a smoothing coefficient.

19. A mobile device, comprising:

one or more processors; and

memory, communicatively coupled to the one or more processors, storing one or more components configured to implement operations comprising:

receiving data as a sequence of input values, the data provided in a frequency domain signal comprising frequency bands and including voice information and noise;

adding a bias value to at least two of the input values of the sequence, the bias values based, at least in part, on a corresponding frequency band;

transforming the data provided in the frequency domain signal comprising frequency bands by applying a first non linear mapping to the input values and the corresponding bias values, a derivative function of the first non linear mapping decreasing in magnitude as the input values increase in magnitude;

smoothing the transformed data, the smoothing being performed by a filter block comprising two inputs, one of the two inputs receiving the transformed data and another of the two inputs receiving speech indicator data from a speech detector;

transforming the smoothed transformed data by applying a second non linear mapping to the smoothed transformed data and the corresponding bias values, the second non linear mapping being opposite to the first non linear mapping;

determining an estimate of a noise level in the data based, at least in part, on the transforming the smoothed transformed data; and

using the determined estimate of the noise level in the data to produce a noise corrected signal.

20. A mobile device as claimed in claim 19 wherein the smoothing comprises smoothing the transformed data using a low pass filter.