vad.m

在语音识别系统中

function [x1,x2] = vad(x)

%幅度归一化到[-1,1]
x = double(x);
x = x / max(abs(x));

%常数设置
FrameLen = 240;                                                            %帧长
FrameInc = 80;                                                             %帧叠

amp1 = 10;
amp2 = 2;
zcr1 = 10;                                                                 %过零率门限
zcr2 = 5;

%maxsilence = 8;                                                           % 6*10ms  = 30ms
maxsilence = 3;                                                            % 3*10ms  = 30ms
minlen  = 15;                                                              % 15*10ms = 150ms
status  = 0;     
count   = 0;
silence = 0;

%计算过零率
tmp1  = enframe(x(1:end-1), FrameLen, FrameInc);
tmp2  = enframe(x(2:end)  , FrameLen, FrameInc);
signs = (tmp1.*tmp2)<0;                                                    %用于存贮相邻2个采样点之间的距离是否相同,即是否穿越零电平
diffs = (tmp1 -tmp2)>0.02;                                                 %计算相邻2个采样点之间的距离,若>0.02,则diffs为1
zcr   = sum(signs.*diffs, 2);

%计算短时能量
amp = sum(abs(enframe(filter([1 -0.9375], 1, x), FrameLen, FrameInc)), 2); %预加重,分帧,加窗


%调整短时能量门限
amp1 = min(amp1, max(amp)/4);
amp2 = min(amp2, max(amp)/8);

%开始端点检测
x1 = 0; 
x2 = 0;
for n=1:length(zcr)
   goto = 0;
   switch status
   case {0,1}                                                              % 0 = 静音, 1 = 可能开始
      if amp(n) > amp1                                                     % 确信进入语音段
         x1 = max(n-count-1,1);
         status  = 2;
         silence = 0;
         count   = count + 1;    
      elseif amp(n) > amp2 | ...                                           % 可能处于语音段
             zcr(n) > zcr2
         status = 1;                                                       %（可能是过滤带）
         count  = count + 1;
      else                                                                 % 静音状态
         status  = 0;
         count   = 0;
      end
   case 2,                                                                 % 2 = 语音段
      if amp(n) > amp2 | ...                                               % 保持在语音段
         zcr(n) > zcr2
         count = count + 1;
      else                                                                 % 语音将结束
         silence = silence+1;
         if silence < maxsilence                                           % 静音还不够长，尚未结束
            count  = count + 1;
         elseif count < minlen                                             % 语音长度太短，认为是噪声（相当于设定最短时间门限）
            status  = 0;
            silence = 0;
            count   = 0;
         else                                                              % 语音结束
            status  = 3;
         end
      end
   case 3,
      break;
   end
end   

count = count-silence/2;
x2 = x1 + count -1;