APPARATUS AND A METHOD FOR ESTIMATING AN OPEN-LOOP PITCH IN A TRANSCODER TO REDUCE QUANTITY OF CALCULATION AND IMPROVE QUALITY OF SOUND

摘要

PURPOSE: An apparatus and a method for estimating an open-loop pitch are provided to reduce quantity of calculation and improve quality of sound in a transcoder between speech codecs of different CELP(Code Excited Linear Prediction) types. CONSTITUTION: A decoding process part(401) decodes a coded bitstream having an input CELP codec format and extracts a closed-loop pitch for each sub-frame of a decoded speech signal from the bitstream. A perception weighting filter(402) performs filtering by perception weighting in view of the decoded speech signal. An open-loop pitch search part(407) searches an open-loop pitch within a search range of the open-loop pitch. The search range is determined by using a decoded closed-loop pitch and a previous open-loop pitch of the same frame. A closed-loop pitch search part(408) searches the closed-loop pitch of a speech signal filtered by perception weighting, by utilizing the searched open-loop pitch, and outputs the searched result as a pitch delay value of an output CELP codec format.