Code excited linear predictive vocoder using virtual searching

A method for encoding speech for communication to a decoder for reproduction and said speech comprises frames with each frame represented by a speech vector having a plurality of samples, comprising the steps of:

• calculating a target excitation vector in response to a present speech vector;
• storing a plurality of candidate excitation vectors having samples in an overlapping table, a group of said candidate excitation vectors having fewer samples than said target excitation vector and a remainder of said candidate excitation vectors having the same number of samples as said target excitation vector;
• calculating an error value associated with each of said plurality of candidate excitation vectors, said error value being a function of its associated candidate excitation vector and said target excitation vector and calculating an error value by repeating for each of said group of candidate excitation vectors a portion of each of said group of said candidate speech vectors so that each of said group of candidate excitation vectors has the same number of samples as said target excitation vector thereby compensating for speech transitions such as between unvoiced and voiced regions of said speech;
• selecting the candidate excitation vector whose calculated error value is the smallest;
• and
• communicating information defining the location of the selected candidate excitation vector in said table.

Apparatus for encoding speech to be communicated to a decoder for reproduction and said speech comprises frames each having a plurality of samples, comprising;

• means for storing a plurality of candidate sets of excitation information each having samples in a table, a group of said sets of excitation information having fewer samples than each of said frames of speech and remaining sets of said sets of excitation information having the same number of samples as each of said frames of speech;
• means for searching through said plurality of candidate sets of excitation information with a present one of said frames to determine the candidate set of excitation information that best matches said present frame by repeating upon searching each of said group of said candidate sets of excitation information a portion of each of said group of said candidate sets of excitation information so that each of said group of said candidate sets of excitation information has the same number of samples as said present frame thereby compensating the amount of matching during speech transitions such as between unvoiced and voiced regions of said speech;
• and
• means for communicating information to identify the location of the determined candidate set of excitation information in said table for reproduction of said speech for said present frame by said decoder.