Code conversion method and device for code conversion

A method of converting code which converts first codes based on a first system to second codes based on a second system, comprising:

• obtaining data of first linear prediction coefficients from said first codes;
• obtaining data of first excitation signal from said first codes;
• storing said data of first linear prediction coefficients;
• storing said data of first excitation signal;
• calculating current data of first linear prediction coefficients from past data of first linear prediction coefficients which are stored;
• calculating current data of first excitation signal from past data of first excitation signal which are stored;
• obtaining data of second linear prediction coefficients from said current data of first linear prediction coefficients;
• and
• obtaining data of second excitation signal from said current data of first excitation signal,
• wherein when said first codes are unavailable, said second codes are obtained by directly using speech parameters which are ever decoded in accordance with said first system and are stored.

A code conversion apparatus, which converts first codes based on a first system to second codes based on a second system, comprising:

• a linear prediction coefficients data decoding circuit configured to obtain data of first linear prediction coefficients from said first codes;
• an excitation signal data decoding circuit configured to obtain data of first excitation signal from said first codes;
• a linear prediction coefficients data storage circuit configured to store said data of first linear prediction coefficients;
• an excitation signal data storage circuit configured to store said data of first excitation signal;
• a linear prediction coefficients data calculating circuit configured to calculate current data of first linear prediction coefficients from past data of first linear prediction coefficients which are stored;
• an excitation signal data calculating circuit configured to calculate current data of first excitation signal from past data of first excitation signal which are stored;
• a linear prediction coefficients data encoding circuit configured to obtain data of second linear prediction coefficients from said current data of first linear prediction coefficients;
• and
• an excitation signal data generating circuit configured to obtain data of second excitation signal from said current data of first excitation signal,
• wherein when said first codes are unavailable, said second codes are obtained by directly using speech parameters which are ever decoded in accordance with said first system and are stored.

A computer program product embodied on a computer-readable medium and comprising code that when executed, causes a computer to perform processes, said computer serving as a code conversion apparatus which converts first codes based on a first system to second codes based on a second system,

• said processes comprising:
• a process of obtaining data of first linear prediction coefficients from said first codes;
• a process of obtaining data of first excitation signal from said first codes;
• a process of storing said data of first linear prediction coefficients;
• a process of storing said data of first excitation signal;
• a process of calculating current data of first linear prediction coefficients from past data of first linear prediction coefficients which are stored;
• a process of calculating current data of first excitation signal from past data of first excitation signal which are stored;
• a process of obtaining data of second linear prediction coefficients from said current data of first linear prediction coefficients;
• and
• a process of obtaining data of second excitation signal from said current data of first excitation signal,
• wherein when said first codes are unavailable, said second codes are obtained by directly using speech parameters which are ever decoded in accordance with said first system and are stored.