Method and apparatus for determining watermark symbols in a received audio signal that can contain echoes, reverberation and/or noise

摘要

Following transmission of a watermarked audio signal over an acoustic path causing echoes, reverberation and/or noise, watermark detection correlation result peak values are concentrated within a limited temporal range around main correlation result peaks, which limited temporal range is much smaller than the total correlation length. The watermark detection is based on the following: given np correlation result peak values v=(v1, v2, . . . , vnp) in an average or expected probability distribution for correlation result values for unmarked content, the probability is calculated that within windows covering the limited temporal range there are np or more values from a correlation result value set greater than or equal to these peaks v.

主权项

1. A method for determining watermark symbols in a received audio signal that contain echoes, reverberation and/or noise, said method comprising:
correlating a section of the received audio signal with at least two different candidate reference pattern signals related to corresponding different candidate watermark symbols is, so as to produce in each case N correlation result values cis for each candidate watermark symbol is; for each candidate watermark symbol is, determining M peak values within said correlation result values cis, for each one of said M peak values denoted global peak values and for each candidate watermark symbol is, determining from the correlation result values cis a corresponding vector visk of np peak values within each one of M windows of length L, each length-L window including one of said M global peak values and the summed-up length of all length-L windows being smaller than N, wherein k=1, . . . , M; for each one of said M windows of length L, calculating a false positive probability value FP(visk) based on the vector visk of peak values and an average or expected probability distribution for correlation result values for a non-watermarked audio signal, wherein the false positive probability FP(visk) is defined as the probability that for one or more times such a length-L window contains np or more correlation result absolute values greater than or equal to the np peak values in an average or expected probability distribution for correlation values for a non-watermarked audio signal; and selecting or the section of said received audio signal that candidate watermark symbol is as a detected watermark symbol which has the minimum false positive probability value minis(mink(FP(visk))) if said minimum false positive probability value minis(mink(FP(visk))) is smaller than a predetermined threshold, wherein otherwise it is decided that no watermark symbol has been detected.