US 5,893,061 AGranted

Method of synthesizing a block of a speech signal in a celp-type coder

AssigneeNokia Mobile Phones Ltd.

InventorUdo Gortz

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Abstract

A new scheme to generate the stochastic excitation for a CELP-type speech codec based upon a hybrid stochastic codebook search technique including use of regular pulse excitation codebooks is described. From the ideal RPE sequence the position of the first nonzero pulse and the position of the pulse with maximum amount as well as the overall sign of the RPE sequence are determined. The corresponding target vectors and pulse responses of the synthesis filter are stored in databases belonging to the positions of the maximum pulse, respectively. These databases are used to derive the stochastic codebook via the so-called LBG-algorithm. Once the codebook has become available, the position of the maximum pulse serves as pre-selection measure to limit the search for the "best" candidate vector to a "small" subset of the stochastic codebook.

Claims4

Dependent claims

A method of synthesizing a block of a speech signal in a CELP-type coder, the method comprising the steps of:

applying an excitation vector to a synthesizer filter of the coder, said excitation vector consisting of two gain normalized components derived from an adaptive codebook and from a stochastic codebook,
for limiting the computational effort of the stochastic codebook components search, computing an ideal Regular Pulse Excitation (RPE) sequence followed by
determining four parameters, namely
the position of the first nonzero pulse of the ideal RPE excitation sequence,
the position of the maximum pulse within said RPE excitation sequence,
the overall sign of the regular pulse excitation sequence defined as the respective sign of said maximum pulse, and
the position of the corresponding part of the pulse codebook, as the position of the maximum pulse,
wherein the method further comprises a step of transmitting said four parameters to a speech decoder.

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Dependencies are inferred from the claim text.