Time-Varying Audio-Signal Level Using a Time-Varying Estimated Probability Density of the Level

• US 20100174540A1
• Filed: 07/11/2008
• Published: 07/08/2010
• Est. Priority Date: 07/13/2007
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Seefeldt, Alan Jeffrey
• Granted Patent: US 9,698,743 B2
• Time in Patent Office: Days
• US Class Current: 704/224
• CPC Class Codes: G06F 18/2321 using statistics or function optimisation, e.g. modelling of probability density functions
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 3/32 the control being dependent upon ambient noise level or sound level

Abstract

Methods, media and apparatus for smoothing a time-varying level of a signal. A method includes estimating a time-varying probability density of a short-term level of the signal and smoothing a level of the signal by using the probability density. The signal may be an audio signal. The short-term level and the smoothed level may be time series, each having current and previous time indices. Here, before the smoothing, computing a probability of the smoothed level at the previous time index may occur. Before the smoothing, calculating smoothing parameters using the probability density may occur. Calculating the smoothing parameters may include calculating the smoothing parameters using the smoothed level at the previous time index, the short-term level at the current time index and the probability of the smoothed level at the previous time index. Calculating the smoothing parameters may include calculating the smoothing parameters using breadth of the estimated probability density.

Claims

1. A method for smoothing a time-varying level of a signal, the method comprising:

estimating a time-varying probability density of a short-term level of the signal; and

smoothing a level of the signal by using the probability density.

2. The method of claim 1 wherein

the signal is an audio signal.

3. The method of claim 1 wherein

the smoothed level and the estimated probability density vary over time at approximately the same rate.

4. The method of claim 1 wherein

the short-term level and the smoothed level are time series, each having current and previous time indices and

before the smoothing, the following is performed:

computing a probability of the smoothed level at the previous time index.

5. The method of claim 1 wherein

before the smoothing, the following is performed:

calculating smoothing parameters using the probability density.

6. The method of claim 5 wherein

the calculating of smoothing parameters comprises

calculating the smoothing parameters using the smoothed level at the previous time index, the short-term level at the current time index and the probability of the smoothed level at the previous time index.

7. The method of claim 5 wherein

the calculating of smoothing parameters comprises

calculating the smoothing parameters using breadth of the estimated probability density.

8. The method of claim 6 wherein

the calculating of smoothing parameters comprises

when the smoothed level at the previous time index has no greater than a threshold probability, using first attack and release time constants;

and

otherwise, when the smoothed level at the previous time index has greater than the threshold probability, using attack and release time constants, one of which is slower than its first-time-constants correspondent.

9. The method of claim 8 wherein the using of attack and release constants comprises

using attack and release time constants, both of which are slower than their first-time-constants correspondents.

10. The method of claim 6 wherein

the threshold probability is variable.

11. The method of claim 10 wherein

the variable threshold probability is a function of the estimated probability density.

12. The method of any one of claims 1-11 wherein the smoothing comprises smoothing the short-term level by using the probability density.

13. The method of any one of claims 1-11 wherein estimating the probability density comprises

fitting a parametric representation to past values of the short-term level.

14. The method of claim 13 wherein the fitting comprises

fitting a Gaussian mixture model to the past values of the short-term level.

15. The method of any one of claims 1-11 wherein estimating the probability density comprises

computing a histogram of past values of the short-term level.

16. A computer-readable memory containing a computer program for performing any one of the methods of claims 1-11.

17. A computer system comprising:

a CPU;

the memory of claim 16; and

a bus communicatively coupling the CPU and the memory.

18. A audio-signal-level smoother comprising:

a short-term-level computer for computing a short-term level of an audio signal;

a level smoother for smoothing level of the audio signal using smoothing parameters;

a probability-density estimator for estimating a probability density of the audio signal;

a probability computer for computing a probability of a delayed smoothed level;

a smoothing-parameters calculator for calculating the smoothing parameters; and

a delay for delaying the smoothed level.

19. The audio-signal-level smoother of claim 18 wherein the probability-density estimator comprises

a probability-density estimator for estimating a probability density using a time series of the short-term level of the audio signal.

20. The audio-signal-level smoother of claim 18 wherein the probability computer comprises

a probability computer for computing the probability using the estimated probability density and the delayed smoothed level.

21. The audio-signal-level smoother of claim 18 wherein the smoothing-parameters calculator comprises

a smoothing-parameters calculator for calculating smoothing parameters using the probability, the delayed smoothed level and the short-term level.

22. The audio-signal-level smoother of claim 19 wherein

the probability computer comprises

a probability computer for computing the probability using the estimated probability density and the delayed smoothed level;

and

the smoothing-parameters calculator comprises

a smoothing-parameters calculator for calculating smoothing parameters using the probability, the delayed smoothed level and the short-term level.

23. The audio-signal-level smoother of claims 18-22 wherein the level smoother comprises

a level smoother for smoothing the short-term level of the audio signal.

24. The audio-signal level smoother of claims 18-22 wherein the probability-density estimator comprises

a fitter for fitting a parametric representation to past values of the short-term level.

25. The audio-signal level smoother of claim 24 wherein the parametric-representation fitter comprises

a fitter for fitting a Gaussian mixture model to the past values of the short-term level.

26. The audio-signal level smoother of claims 18-22 wherein the probability-density estimator comprises

a histogram computer for computing a histogram of past values of the short-term level.

27. A method for smoothing a time-varying level of a signal, the method comprising:

receiving a signal having a short-term level; and

smoothing the time-varying level,

wherein

the short-term level and the smoothed time-varying level are time series, each having current and previous time indices and

the smoothing comprises

using slow time constants where the difference between the smoothed short-term level at the previous time index and the short-term level at the current time index exceeds a threshold directing the use of fast time constants.