Patent CA-2374725-A1 (CA)
Title: Voice decode apparatus with packet error resistance, voice encoding decode apparatus and method thereof
Inventor: SERIZAWA MASAHIRO
IPC: G10L19/16
Filed: 2002-03-06
Abstract: In case that a determination result transferred from a loss detection circuit 25 shows that frame loss exists, a reuse packet detection circuit 30 obtains the generation time of loss packet from the packet transferred from a reception buffer circuit 10 and records it. Next, in case that the recorded generation time coincides with the generation time of the packet transferred from a packet input terminal 5, a command for recalculating excitation signals is transferred to an excitation code buffer circuit 40, a past excitation signal generation circuit 60 and an updated excitation signal buffer circuit 55 , together with the generation time of the loss packet which arrived late. The excitation code buffer circuit 40 accumulates the voice source signal and the codes of a pitch filter, which were transferred from a code division circuit 35, until the past for a time period corresponding to the predetermined number of packets. In order to use packets which are received late, it is required that the number of these packets is longer than reception buff er length. Also, when receiving the recalculation command of the excitation signals from the reuse packet detection circuit 30 , the excitation code buffer circuit 40 transfers the codes being accumulated after the transferred loss packet generation time to a past excitation generation circuit 60. When receiving the recalculation command of the excitation signals from the reuse packet detection circuit 30, by using the codes of the excitation signals,  which were transferred from the excitation code buffer circuit 40, the past excitation signal generation circuit 60 conducts the decode processing of the excitation signals up to a frame prior to a frame being presently processed from a retroactive frame, packet of which was lost . The decode processing is the same as one conducted by a voice source signal circuit 49, a pitch filter circuit 50 and an excitation signal buffer 54. In the frame in which this processing is conducted, with regard to the generation of the excitation signals, the quantity of operation becomes times as much as the frame number from the frame, packet of which was lost, to the frame being presently processed. The quantity of operation depends on the number of the packets which are retroactively detected in the reuse packet detection. Finally, the excitation signals recalculated up to the prior frame are transferred to an updated excitation signal buffer circuit 55. The updated excitation signal buffer circuit 55 accumulates the excitation signals E transferred from the pitch filter circuit 50 for a predetermined time period in the past, and transfers the accumulated excitation signals to the pitch filter circuit 50.        In case that the recalculation command of the excitation signals is transferred from the reuse packet detection circuit 30, after the excitation signals being already accumulated are replaced with the excitation signals recalculated by the past excitation signal generation circuit 60, these excitation signals are transferred to the pitch filter circuit 50.