Compressed domain automatic level control based on ITU-T G.722.2

In order to control the speech level automatically in the 3G mobile networks where Transcoder Free Operation (TrFO) is adopted, a compressed domain automatic level control (ALC) method is proposed based on ITU-T G.722.2 speech codec. The level of decoded speech is first measured by P.56 tool. Then, based on the difference between the measured level and the target level, the gain of ALC is calculated. Finally, the codebook gain parameters of speech codec are modified according to the ALC gain and the level of decoded speech is adjusted to the target level. The result of performance evaluation shows that, in comparison with the traditional method, in which the speech signal is first decoded, then level adjusted by ITU-T P.56 tool, and finally re-encoded, the proposed method saves 65% to 75% of the computational complexity. The difference between the output level and the target level is smaller and the objective speech quality is much better.