| 摘要 |
PURPOSE:To obtain a high quality sound at a low bit rate with less noise by searching adaptive code book and providing a smooth pitch change. CONSTITUTION:An adaptive code book searching circuit 7 delays the past sound source against the delay which is longer than a subframe length and evaluation measures and gains are computed to produce influence subtraction signals SE and a delay D1, which is an optimum delay within a search region, is obtained. At the same time, an adaptive code book searching circuit 8 changes the delay value for every repeat against the delay which is less than a subframe length, computes gains and evaluation measures, computes evaluation measure equivalent to a subframe length and gain and obtains a delay D2 which is an optimum delay within the searching region. Then, an optimum delay determining circuit 9 decides the optimum delay, which makes the evaluation measure a minimum, from the delays D1 and D2 and generates an adaptive code sound source SA which is the corresponding sound source signals. If the delay is less than the subframe length, the sound source SA is made by a simple repetition. |
