3G语音链路中自动增益控制模块的实现和改进

Implementation and improvement of auto gain control in the 3G mobile terminal

针对3G终端通话时语音不够平滑圆润的问题,提出在3G上行和下行语音链路中增加自动增益控制(automatic gain control,AGC)模块。AGC模块通过自适应更新增益值算法能够防止通话过程中的语音幅度过大,从而避免语音数据经过数字增益后发生溢出,同时能对小信号进行有效地放大,对时域语音质量进行均衡,使通话双方感到语音质量自然流畅。但是如果不对现有AGC算法进行改进,处理后的语音中会产生非线性失真。改进后的AGC不仅可以使输出语音的幅值在一个预先规定的范围内,根据预先设定的门限值,放大小信号,限制强信号,防止通话过程中的语音信号过载,同时能避免非线性失真。经过理论评估和实际验证,该模块能够有效地放大小信号,限制强信号,从而增强移动终端通话质量。

The 3G mobile terminal speaking voiee is not smooth, so we suggested adding the automatic gain control（AGC） module in the uplink and downlink voice link of the 3G mobile terminal. At the same time, by adapting to update gain values algorithm, the AGC module can avoid audio too large amplitude which has led to audio data overflow after passing data gain module. The AGC Module can amplifying small audio signal effectively. This will make audio quality reach equilibri- um,which make the voice smooth to both sides. However, if an existing AGC algorithm has not been improved, the non-linear distortion will occur in processing the voice. The AGC which was proposed in this article will make the output of voice at predetermined amplitude, according to pre-determined threshold value, amplify weak signal, suppress strong signal, prevent overload of audio signal in the processing of call and avoid nonlinear distortion. The academic evaluations and practice tests proved that the AGC module can amplify weak signal effectively and prevent the overload of the strong signal, thereby enhancing the quality of mobile communication terminal calls.