| 摘要 |
In an encoder device which is for use in combination with a decoder device in a communication system and which encodes a sequence of digital speech signals into a sequence of output signals by the use of a spectrum parameter and pitch parameters, a primary pulse producing unit calculates a first set of prediction excitation multipulses by the use of the spectrum parameter and the pitch parameters with respect to a preselected one of subframes which result from dividing every frames and produces the first set of prediction excitation multipulses and a sequence of primary synthesized signals specified by the first set of prediction excitation multipulses and the spectrum parameter and the pitch parameters. A subtracter subtracts the primary synthesized signals from the digital speech signals and produces a sequence of difference signals representative of differences between the primary synthesized signals and the digital speech signals. Supplied with the difference signals, a secondary pulse producing unit calculates a predetermined number of secondary excitation multipulses by the use of the spectrum parameter and the pitch parameters. Alternatively, the encoder device may comprise a periodicity detector supplied with the spectrum parameter for detecting whether or not periodicity of an impulse response of a synthesis filter determined by the spectrum parameter is higher than a predetermined threshold level. The periodicity detector produces a weighting signal representative of a weighted value when the periodicity is higher than the predetermined threshold level. The spectrum parameter is weighted on production of the weighted signals. |
