GENERATING SAMPLE ERROR COEFFICIENTS

• US 20080106249A1
• Filed: 10/19/2007
• Published: 05/08/2008
• Est. Priority Date: 11/03/2006
• Status: Active Grant

• Current Assignee: Psytechnics Ltd. (NetScout Systems Incorporated)
• Original Assignee: Psytechnics Ltd. (NetScout Systems Incorporated)
• Inventors: Barrett, Paul, Malfait, Ludovic
• Granted Patent: US 8,548,804 B2
• Time in Patent Office: Days
• US Class Current: 324/76.38
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• CPC Class Codes: G10L 21/04 Time compression or expansion
• CPC Class Codes: G10L 25/69 for evaluating synthetic or decoded voice signals

Abstract

This invention relates to generation of a sample error coefficient suitable for use in an audio signal quality assessment system. The invention provides a method of determining a sample error coefficient between a first signal and a similar second signal comprising the steps of: determining a first periodicity measure from the first signal; determining a second periodicity measure from the second signal; generating a ratio in dependence upon said first periodicity measure and said second periodicity measure; and determining a sampling rate error coefficient in dependence upon said ratio.

Claims

1. A method of determining a sample error coefficient between a first signal and a similar second signal comprising the steps of:

a) determining a first periodicity measure from the first signal;

b) determining a second periodicity measure from the second signal;

c) generating a ratio in dependence upon said first periodicity measure and said second periodicity measure; and

d) determining a sampling rate error coefficient in dependence upon said ratio.

2. A method according to claim 1, in which the first signal is a first known signal to be transmitted via a communications channel and the second signal is a first received signal, being a possibly degraded version of said first known signal, received via said communications channel.

3. A method according to claim 2, in which the first known signal is a signal comprising a tone.

4. A method according to claim 3, in which the first known signal is a signal comprising a plurality of tones.

5. A method according to claim 1, in which the steps a) and b) of determining a periodicity measure comprise the step of determining the pitch period of each signal.

6. A method according to claim 5, in which the pitch period is determined in dependence upon the position of a peak in the autocorrelation function of each signal.

7. A method according to claim 1, in which the steps a) and b) are determined in dependence upon the frequency of one or more peaks in the Fourier Transform of each signal.

8. A method according to claim 1, in which the first signal is separated into segments and for each of a plurality of segments of the first signal a segment sampling rate error is determined in accordance with the steps of:

selecting a segment of the second signal where a similarity measure exceeds a predetermined threshold; and

determining a segment sample rate error coefficient in dependence upon a segment first periodicity measure and a segment second periodicity measure;

and wherein the sampling rate error coefficient is determined at step d) in dependence upon the plurality of segment sample rate coefficients so obtained.

9. A method according to claim 8, in which the said plurality of segments of the first signal comprises segments having a periodic component.

10. A method according to claim 8, in which the plurality of segment sample rates are used to form a histogram and the sampling rate error coefficient is determined at step d) by selecting a value from the histogram bin having the greatest number of coefficients.

11. A method according to claim 10, in which said value is selected by generating an average of the values in the histogram bin having the greatest number of coefficients.

12. A method according to claim 8, in which the plurality of segment sample rates are used to form a histogram and the sampling rate error coefficient is determined at step d) by interpolating between multiple histogram bins.

13. A method of estimating the quality of a communications channel comprising the steps of

e) transmitting a second known signal via said communications channel;

f) receiving a second received signal, being a possibly degraded version of said known signal, via said communications channel

g) comparing a copy of the second known signal to the second received signal; and

h) generating a quality measure based on said comparison;

characterised in that;

the comparing step comprises the sub-steps of;

i) determining a sampling rate error coefficient according to the method of any one of claims 1;

j) resampling the received signal in dependence upon said sampling rate error coefficient to generate a resampled signal; and

k) comparing the known signal to the resampled signal.

14. A method according to claim 13, in which the first known signal comprises the second known signal and the first received signal comprises the second received signal.

15. A method according to claim 13 in which the resampling step j) is performed using a truncated sin(x)/x transfer function.

16. A computer readable medium carrying a computer program for implementing the method according to claim 1.