Importance

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Abstract

Apparatus and methods are disclosed for recovering alignment from a non-ideally encoded multi-bit digital signal without the need to embed framing information within the encoded signal or append framing bits thereto. In particular, the invention is disclosed in the context of recovering septet alignment in a sub-band ADPCM (adaptive differential pulse code modulated) 7 kHz audio digital signal without the need to embed any framing information within the digital signal itself. Specifically, in this context, this method relies on first gathering statistics from a 56 kbit/second 7 kHz audio digital signal itself for a pre-defined number of incoming bits that occur during a measurement interval and for every one of seven possible alignments for a septet. Once these statistics are gathered, the alignment is selected to be that which satisfies various pre-defined statistical tests that are dictated by non-uniform deterministic characteristics that occur in the ADPCM audio digital signal itself, once it is properly aligned, and specifically certain characteristics which exist in a distribution of the occurrences of the different combinations of the four most significant bits of the low-band ADPCM codewords situated within properly aligned ADPCM septets that occurred during the measurement interval.

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First Claim