The Standard

Qualcomm Code Excited Linear Prediction (QCELP) 13-kbps voice coder is the North American speech service option standard for wideband spread spectrum digital communication systems TIA-IS733. The coder supports four basic rates namely 13.3, 6.2, 2.7 and 1 kbps respectively. The vocoder works on the principle of CELP but differs from the traditional CELP in that it dynamically adjusts the encoded rate based on speech signal energy, background noise and other speech characteristics.

The coder works on a frame of 160 speech samples (20 msec), and a look ahead of 60 samples (7.5 msec) is required. So the algorithmic delay for the coder is 27.5 msec.

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