| 摘要 |
Disclosed is a code converting apparatus for converting a first code sequence conforming to a first system to a second code sequence conforming to a second system, in which a speech decoding circuit (1500) acquires first linear prediction coefficient and the information on an excitation signal from the first code sequence, and actuates a filter having the aforementioned first linear prediction coefficient with the excitation signal obtained from the information on the excitation signal, to generate a first speech signal. A gain code generating circuit (1400) calculates a gain minimizing the distance between a second speech signal, generated from the information, obtained from the second code sequence, and the first speech signal (optimum gain), and corrects the optimum gain. The gain code generating circuit then finds the gain information in the second code sequence, based on the optimum gain as corrected (optimum gain corrected), the above optimum gain and a gain read out from a gain codebook of the second system. The gain is found at this time, in a non-speech segment, based on a speech decision value, using an evaluation function which will reduce time variations of the gain of the second system. <IMAGE>
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