Patent ID: 7373298

Claim:
An excitation signal coding apparatus for increasing the correlation between a synthesized speech signal and an input speech signal, the apparatus comprising: a first excitation codebook section that: generates for each of a plurality of prospective first excitation vectors a corresponding first synthesized vector, subtracts each of the generated first synthesized vectors from a first target vector, representing the input speech signal, to produce a residual vector, multiplies the first target vector by predetermined coefficients to produce a second target vector, identifies which of the prospective first excitation vectors corresponds to the residual vector having the minimal difference with the second target vector, and identifies the residual vector having the minimal difference with the second target vector; a second excitation codebook section that: generates for each of a plurality of prospective second excitation vectors a corresponding second synthesized vector, and identifies which of the prospective second excitation vectors corresponds to the generated second synthesized vector having the minimal difference with an identified residual error; and a summer that sums the identified first and second excitation vectors to produce an excitation signal; and a generator that generates the synthesized speech signal with the excitation signal.