Patent ID: 8769294

Claim:
Digital signature generation apparatus, comprising a processing device configured to digitize a media signal to obtain a sampled data segment; an envelope generator coupled to the processing device and configured to generate an envelope representation, of only one polarity, of the sampled data segment, the envelope generator comprising (i) a provider coupled to the processing device and configured (a) to remove samples in the sampled data segment which are of polarity opposite to the one polarity, or (b) to reverse the polarity of samples in the sampled data segment which are of polarity opposite to the one polarity, to provide a polarized data segment and (ii) a sample value summer coupled to the processing device and configured, for each of successive portions of the polarized data segment, each portion comprising a predetermined plurality of samples, to provide a portion sum value as the sum of the values of the samples in the portion, thereby to provide said envelope representation; a threshold value generator coupled to the processing device and configured to determine threshold values for each of successive blocks of the envelope representation, each block comprising a plurality of the successive portions, each threshold value being determined based on a par value of the portion sum values of the portions comprised in the block concerned, or operable to determine a threshold value for each portion of the envelope representation, each threshold value being derived from (A) the threshold of the preceding portion, and (B) the current portion sum value and (C) a multiplication factor; an event detector coupled to the processing device and configured to detect, as an event, a transition of one of the portion sum values across the threshold value for the block to which the portion concerned belongs, or a transition of one of the portion sum values across the threshold value for the portion concerned; and a signature generator coupled to the processing device and configured in response to the detected event to generate a digital signature characteristic of the sampled data segment.