Adjustable noise suppression system
Methods and corresponding systems for suppressing noise in an input signal include setting a minimum overall gain in a noise reduction processor for processing a first frame of data associated with the input signal. In response to a new minimum overall gain being set, the minimum overall gain in the noise reduction processor is replaced with the new minimum overall gain, and a second frame of data associated with the input signal is processed to suppress noise using the new minimum overall gain. The new minimum overall gain can be a function of the input signal or an output signal of the noise reduction processor. The new minimum overall gain can correspond to a difference between an estimated signal-to-noise ratio (SNR) improvement that is calculated using time-domain data and a target SNR improvement.
1. A method of suppressing noise in an input signal comprising:
setting a minimum overall gain in a noise reduction processor for processing a first frame of data associated with the input signal;
replacing, in response to a new minimum overall gain being set, the minimum overall gain in the noise reduction processor with the new minimum overall gain; and
processing a second frame of data associated with the input signal to suppress noise using the new minimum overall gain.
2. The method of suppressing noise according to claim 1 wherein the replacing the minimum overall gain comprises replacing the minimum overall gain with the new minimum overall gain, wherein the new minimum overall gain is a function of one or more of the input signal and an output signal of the noise reduction processor.
3. The method for suppressing noise according to claim 1 comprising:
outputting from the noise reduction processor a noise indicator; and
calculating the new minimum overall gain using the input signal, an output signal, the noise indicator, and a reference signal.
4. The method for suppressing noise according to claim 1 wherein the replacing the minimum overall gain comprises:
estimating, using time domain data, a signal to noise ratio (SNR) improvement of the noise reduction processor;
computing the new minimum overall gain corresponding to a difference between a target SNR improvement and the estimated SNR improvement; and
replacing the minimum overall gain in the noise reduction processor with the new minimum overall gain.
5. The method for suppressing noise according to claim 4 wherein the computing the new minimum overall gain comprises computing the new minimum overall gain using a least mean squares (LMS) algorithm and the difference between the target SNR improvement and the estimated SNR improvement.
6. The method for suppressing noise according to claim 4 comprising updating the target SNR improvement.
7. The method for suppressing noise according to claim 4 comprising initially setting the minimum overall gain to a negative value of the target SNR improvement.
8. A system for suppressing noise in an input signal comprising:
a frequency domain converter adapted to convert the input signal to a frequency domain signal;
a noise estimator adapted to estimate a noise level in the frequency domain signal;
a gain calculator adapted to calculate a gain based upon the estimated noise level and a minimum gain control signal, wherein the minimum gain control signal varies with a desired level of noise suppression;
a gain adjuster adapted to change the amplitude of the frequency domain signal based upon the gain to produce a filtered signal; and
a time domain converter adapted to convert the filtered signal to an output signal in a time domain, wherein
the system further comprises:
a post-filter analyzer coupled to the input signal and the output signal, for producing an improvement signal; and
a minimum gain adapter coupled to the improvement signal and a reference signal for producing the minimum gain control signal.
9. The system for suppressing noise according to claim 8 wherein the minimum gain control signal is responsive to a signal to noise ratio (SNR) of the input signal, an SNR of the output signal, and a target SNR.
10. The system for suppressing noise according to claim 9 further comprising a noise indicator having an input coupled to the frequency domain signal, an input coupled to the SNR of the input signal, and having a noise indicator output signal responsive to a sample of the input signal being noise.
11. The system for suppressing noise according to claim 8 wherein the improvement signal is an SNR improvement signal responsive to a difference between an SNR of the input signal and an SNR of the output signal, and wherein the reference signal is an SNR target signal.
12. The system for suppressing noise according to claim 8 wherein the improvement signal is responsive to the noise indicator output signal.
13. A noise suppression device having adjustable noise suppression comprising:
a noise suppressor having a noise suppressor input, a noise suppressor output, a noise indicator output, and a minimum gain control input; and
a noise suppressor controller having inputs coupled to the noise suppressor input, the noise suppressor output, and the noise indicator output, and having an output for outputting a minimum gain control signal, wherein the minimum gain control signal is coupled to the minimum gain control input, wherein the noise suppressor is adapted to have a minimum gain controlled by the minimum gain control signal.
14. The noise suppression device according to claim 13 wherein the noise suppressor comprises:
a frequency domain converter coupled to the noise suppressor input;
a gain modifier coupled to an output of the frequency domain converter;
a time domain converter having an input coupled to a gain modifier output, and an output coupled to the noise suppressor output; and
a gain calculator having an input coupled to the minimum gain control signal, and an output coupled to the gain modifier and adapted to control the gain modifier in response to the minimum gain control signal.
15. The noise suppression device according to claim 14 wherein the noise suppressor comprises:
an energy estimator having an input coupled to the output of the frequency domain converter;
a noise estimator having an input coupled to an output of the energy estimator; and
a signal-to-noise ratio (SNR) estimator having an input coupled to the output of the energy estimator, and an output coupled to an input of the gain calculator.
16. The noise suppression device according to claim 13 wherein the noise suppressor controller comprises:
a post-filter analyzer having inputs coupled to the noise suppressor input, and the noise suppressor output, and having an improvement signal output; and
a minimum gain adapter having an input coupled to the improvement signal, an input coupled to a reference signal, and an output for outputting the minimum gain control signal.
17. The noise suppression device according to claim 16 wherein the post-filter analyzer has an input coupled to the noise indicator output.
18. The noise suppression device according to claim 16 wherein the minimum gain adapter has an input coupled to the noise indicator output.
19. The noise suppression device according to claim 13 comprising:
an echo canceller having an output coupled to the noise suppressor input; and
a level controller having an input coupled to the noise suppressor output.