Timing recovery scheme for packet speech in multiplexing environ

Details Timing recovery scheme for packet speech in multiplexing environ Timing recovery scheme for packet speech in multiplexing environ

1995-05-18

1997-12-16

MacDonald, Allen R.

Multiplex communications

Wide area network

Packet switching

395 217, 395 219, 395 232, 370505, G10L 914, H04J 307

Patent

active

056994818

ABSTRACT:
Multiple speech bit-stream frame buffers are used between the controller and the speech decoder. Whenever excessive or missing speech packages are detected, the speech decoder switches to a special corrective mode. If there is too much, the buffered frames are played out fast; if there is too little the buffered frames are played out slowly. For the fast play, some speech information has to be discarded, while for the slow play some speech-like information has to be synthesized. The speech may be handled in sub-frame units, which may be 52 samples at a time. Low energy, silent or unvoiced sub-frames, which also indicate non-periodicity, are detected and manipulated. Moreover, the decoded signal is manipulated at the excitation phase, before the final LPC synthesis filter, resulting in a transparent perceptual effect on the manipulated speech quality. Additionally, the buffers are enlarged such that the problem caused by controller asynchronicity is eliminated. Further, for bulk delay caused by multiplexing data and speech transmissions, the buffers maintain the smallest number of speech packets necessary to prevent buffer underflow during a data packet transmission while minimizing speech delay and preserving data transmission efficiency.

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M.M. Lara-Barron and G.B. Lockhart, "Speech Encoding and Reconstruction for Packet-Based Networks", IEE Colloquium No. 199: Coding for Packet Video and Speech Transmission, Sep. 1992.
M.H. Sherif and A. Crossman, "Overview of Speech Packetization", IEEE 1995 Symposium on Computers and Communications, Jun. 1995.

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