| 摘要 |
In an LPC type coded communications system the excitation source is derived from previous filter outputs at the decoder; in one embodiment the speech output is used, in other embodiments, intermediate excitation outputs are used. To enable tracking the coder derives the filter parameters by using the same excitations, supplied by a local decoder, to synthesise locally the actual error produced at the decoder; the parameters are optimised iteratively by varying the delay of an FIR stage and deriving the actual error in a loop, and selecting the delay for minimum actual error. The IIR parameters may be calculated jointly with the other FIR parameters inside the loop, either for minimum prediction error or minimum actual error. The FIR stage may comprise several parallel FIRs, separately excited. |
