| 摘要 |
PURPOSE:To obtain satisfactory sound quality with a low bit rate by reducing an arithmetic quantity while allowing a long period prediction means searching an adaptive code vector expressing the pitch correlation of a voice signal to make delay codes change while thining them. CONSTITUTION:The delay code uniformly thining variable circuit 168 of a long period prediction circuit 16A makes delay codes change while thining them uniformly within the size of a code book to set delay codes (d) of processing objects. Then, an adaptive code vector ed (n) generating processing an adaptive code vector generating circuit 162, a weighted adaptive code vector H.ed (n) generating processing by a synthetic filter 163 and an evaluation function Cd<2>/Gd calculating processing by an evaluation function calculating circuit 164 are performed at every delay code. After these processing are performed to all delay codes (d) of variable objects, a delay code making the evaluation function Cd<2>/Gd maximum is determined as an optimum delay code CD by an optimum delay code determining circuit 165 to be outputted. Thus, the arithmetic quantity at the time of a long period prediction is reduced. |
