Coded speech communication system having code books for synthesizing small-amplitude components

In coded speech communication, discrete speech samples are analyzed to generate a first signal indicating the fine pitch structure of the speech samples and a second signal indicating their spectral characteristic. The amplitudes and locations of main excitation pulses are determined from the fine pitch structure and spectral characteristic and a third signal indicating the determined pulse amplitudes and locations is generated. The difference between the speech samples and the main excitation pulses is detected and used in auxiliary excitation pulse calculation to determine gain and index values of auxiliary excitation pulses by retrieving stored auxiliary excitation pulses from a code book so that the retrieved auxiliary excitation pulses approximate the difference. The first, second and third coded signals and the gain and index values are transmitted through a communication channel to a distant end where a replica of the main excitation pulses is recovered from the received first and third signals and a replica of the auxiliary excitation pulses is recovered from a code book in response to the received fourth signal. These replicas are modified with the second signal to recover a replica of the original speech samples.