语音自适应端点检测 adaptive VAD 以及短时能量和过零率相结合的两级判别法

端点检测 语音端点检测就是检测语音信号的起点和终点，因此也叫起止点识别。在语 音识别中，一个关键问题就是如何将语音信号精确地检测出来，为获得准确的识 别提供前提。 1．基于短时能量和过零率相结合的两级判别法 以能量E和过零率ZCR为特征的起止点算法的根据是背景噪声与语音的短时 段及特征从统计看都有相当的区别。 设语音波形时域信号为x (l)，加窗分帧处理后得到第n帧语音信号为 先用短时能量作第一次判别，在此基础上用短时过零率作第二次判别。在用 短时能量作第一次判别时，为了不至于把语音能量的局部下降点错误地当成起止 点，常采用双门限比较的方法。 代码： %设置初始量 frameSize=256;%帧长 overlap=128;%重叠 deltaEnergyLevel1=-20;%短时能量的两个门限 deltaEnergyLevel2=-10; zcrRatio=0.2;%短时过零率门限 %读入语音文件 [filename,pathname]=uigetfile('D:\*.wav','open file:'); [y,fs,nbits]=wavread([pathname,filename]);%Reads input wav file %消除DC电平偏移 y=y-mean(y); %分帧 framedY=buffer(y,frameSize,overlap); frameNum=size(framedY,2);%Number of frames %计算短时能量和门限 energy=frame2logEnergy(framedY); energyLevel1=max(energy)+deltaEnergyLevel1; energyLevel2=max(energy)+deltaEnergyLevel2; %计算短时过零率和门限 zcr=zcrate(framedY-0.03);%0.03设置噪声门限 zcrThreshold=max(zcr)*zcrRatio; %根据较高的门限找到起止点 voicedIndex=find(energy>=energyLevel2); sound=[]; k=1; sound(k).begin=voicedIndex(1); for i=2:length(voicedIndex)-1, if voicedIndex(i+1)-voicedIndex(i)>1, sound(k).end=voicedIndex(i); sound(k+1).begin=voicedIndex(i+1); k=k+1; end end sound(k).end=voicedIndex(end); %忽略一些小的细节 index=[];for i=1:length(sound), if(sound(i).end-sound(i).begin)<3 index=[index,i]; end end sound(index)=[]; %根据较低的门限进一步判断 for i=1:length(sound), head=sound(i).begin; while(head-1)>=1&energy(head-1)>=energyLevel1, head=head-1; end sound(i).begin=head; tail=sound(i).end; while(tail+1)<=length(energy)&energy(tail+1)>energyLevel1, tail=tail+1; end sound(i).end=tail; end %根据zcr门限判断起止点 for i=1:length(sound), head=sound(i).begin; while(head-1)>=1&zcr(head-1)>=zcrThreshold, head=head-1; end sound(i).begin=head; tail=sound(i).end; while(tail+1)<=length(zcr)&zcr(tail+1)>zcrThreshold, tail=tail+1; end sound(i).end=tail; end %去掉重复的语音帧 if length(sound)~=0, index=[]; for i=1:length(sound)-1, if sound(i).begin==sound(i+1).begin&sound(i).end==sound(i+1).end, index=[index,i]; end end sound(index)=[];end; %将序列变换成整段语音的样点序列 if length(sound)~=0, for i=1:length(sound), out(i).begin=(sound(i).begin-1)*(frameSize-overlap)+1; out(i).end=(sound(i).end)*(frameSize-overlap)+overlap; end else out=[]; end; %画图显示 subplot(3,1,1); plot((1:length(y))/fs,y); axis([-inf inf-1 1]); ylabel('Amplitude'); title('Wave form'); subplot(3,1,2); time=((0:frameNum-1)*(frameSize-overlap)+0.5*frameSize)/fs; plot(time,energy,'.-'); line([min(time),max(time)],energyLevel1*[1 1],'color','c'); line([min(time),max(time)],energyLevel2*[1 1],'color','c'); axis tight ylabel('Log energy(dB)'); title('Log energy'); subplot(3,1,3); plot(time,zcr,'.-'); line([min(time),max(time)],zcrThreshold*[1 1],'color','c'); axis([-inf inf 0 inf]); ylabel('ZCR'); title('Zero crossing rate'); %Plot end points subplot(3,1,1); yBound=[-1 1]; for i=1:length(sound), line(sound(i).begin*(frameSize-overlap)/fs*[1,1],yBound,'color','r'); line(sound(i).end*(frameSize-overlap)/fs*[1,1],yBound,'color','g'); end %Plot end points subplot(3,1,2); yBound=[min(energy)max(energy)]; for i=1:length(sound), line(sound(i).begin*(frameSize-overlap)/fs*[1,1],yBound,'color','r');line(sound(i).end*(frameSize-overlap)/fs*[1,1],yBound,'color','g'); end %Plot end points subplot(3,1,3); yBound=[0 max(zcr)]; for i=1:length(sound), line(sound(i).begin*(frameSize-overlap)/fs*[1,1],yBound,'color','r'); line(sound(i).end*(frameSize-overlap)/fs*[1,1],yBound,'color','g'); end %短时能量 function logEnergy=frame2logEnergy(framedY) %frame2logEnergy Frame to log energy conversion meanSquare=mean(framedY.^2); meanSquare(meanSquare==0)=eps;%To avoid"log(0)"warning logEnergy=10*log10(meanSquare); %短时过零率 function count=zcrate(frame) count=sum(diff(sign(frame))~=0); count=count/(2*(length(frame)));