System for comfort noise injection

1. A noise injection system for adding comfort noise to an audio signal, comprising:

a background noise estimator configured to determine spectral content of a background noise associated with the audio signal when speech is detected in the audio signal;

a comfort noise generator configured to generate a comfort noise signal having a randomized phase;

a gain circuit configured to calculate a gain value for adjusting the comfort noise signal based on the determined spectral content of the background noise to generate a gain-adjusted comfort noise signal; and

a combining circuit configured to combine the gain-adjusted comfort noise signal and the audio signal to generate an output signal when speech is not detected in the audio signal.

2. The system of claim 1 wherein the background noise estimator determines spectral content in the presence of speech in the audio signal.

3. The system of claim 2 wherein the background noise is present at a source of the speech.

4. The system of claim 3 wherein the source of the speech comprises a speaker.

5. The system of claim 1 wherein the generated comfort noise is included when the speech is not detected.

6. The system of claim 5 wherein the generated comfort noise is included in the gaps in the speech.

7. The system of claim 6 wherein the generated comfort noise mimics the background noise.

8. The system of claim 1 further comprising:

an analysis filter configured to filter time domain input data on a block basis using overlapping blocks of the time domain input data, the time domain input data representing an input signal;

a first conversion circuit configured to convert the time domain input data into the frequency domain data;

a second conversion circuit configured to convert the frequency domain output data into time domain output data; and

a synthesis filter configured to filter the time domain output data.

9. The system of claim 8 where the gain circuit comprises:

a ripple compensator configured to adjust the gain value to compensate for an energy increase due to ripples caused by processing in an overlapping block manner;

a coherency mismatch compensator configured to adjust the gain value to compensate for data coherence mismatch caused by a phase randomization and processing in an overlapping block manner; and

a window compensator configured to adjust the gain value to compensate for a loss in energy due to the filtering of the time domain input data and/or the time domain output data.

10. A method for adding comfort noise to an audio signal, comprising:

determining spectral content of a background noise associated with the audio signal when speech is detected in the audio signal;

generating a comfort noise signal having a randomized phase;

calculating a gain value for adjusting the comfort noise signal based on the determined spectral content of the background noise to generate a gain-adjusted comfort noise signal; and

combining the gain-adjusted comfort noise signal and the audio signal to generate an output signal when speech is not detected in the audio signal.

11. The method of claim 10 wherein the determining is with a background noise estimator.

12. The method of claim 10 wherein the generating is with a comfort noise generator.

13. The method of claim 10 wherein the calculating is with a gain circuit.

14. The method of claim 10 wherein the combining is with a combining circuit.

15. A noise injection system for injecting comfort noise into an audio signal, comprising:

a background noise estimator configured to determine spectral content of a background noise associated with the audio signal when speech is detected in the audio signal;

a comfort noise generator configured to generate a comfort noise signal having a randomized phase;

a gain circuit configured to calculate a gain value for adjusting the comfort noise signal based on the determined spectral content of the background noise to generate a gain-adjusted comfort noise signal, wherein the gain-adjusted comfort noise signal approximates the background noise; and

a combining circuit configured to combine the gain-adjusted comfort noise signal and the audio signal to generate an output signal, wherein the combination of the gain-adjusted comfort noise signal is at gaps when speech is not detected in the audio signal.

16. The system of claim 15 wherein the background noise estimator determines spectral content in the presence of speech in the audio signal.

17. The system of claim 16 wherein the background noise is present at a source of the speech.

18. The system of claim 17 wherein the source of the speech comprises a speaker.

19. The system of claim 15 further comprising:

an analysis filter configured to filter time domain input data on a block basis using overlapping blocks of the time domain input data, the time domain input data representing an input signal;

a first conversion circuit configured to convert the time domain input data into the frequency domain data;

a second conversion circuit configured to convert the frequency domain output data into time domain output data; and

a synthesis filter configured to filter the time domain output data.

20. The system of claim 19 where the gain circuit comprises:

a ripple compensator configured to adjust the gain value to compensate for an energy increase due to ripples caused by processing in an overlapping block manner;

a coherency mismatch compensator configured to adjust the gain value to compensate for data coherence mismatch caused by a phase randomization and processing in an overlapping block manner; and

a window compensator configured to adjust the gain value to compensate for a loss in energy due to the filtering of the time domain input data and/or the time domain output data.