Speech coder

A speech coder includes an LPC analyzer, a difference signal generating section, a first code book, a second code book, and a multiplexer. The LPC analyzer divides an input discrete speech signal into signal components in units of frames each having a predetermined time length, and obtains a spectrum parameter representing a spectrum envelope of the speech signal. The difference signal generating section obtains a difference signal by dividing the frame into subframes each having a predetermined time length, and predicting a pitch parameter representing a long-term correlation on the basis of a past sound source signal. The first code book stores a signal formed beforehand by learning based on the difference signal. The second code book stores a signal having predetermined characteristics or a signal formed beforehand by learning. The multiplexer represents a sound source signal of the speech signal by a linear combination of a signal selected from the first code book in accordance with each obtained difference signal and a signal selected from the second code book, and outputs the combination.