关于MATLAB中的语音信号检测程序

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;
FrameInc = 80;

amp1 = 10;
amp2 = 2;
zcr1 = 10;
zcr2 = 5;

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

%计算过零率
tmp1 = enframe(x(1:length(x)-1), FrameLen, FrameInc);
tmp2 = enframe(x(2: length(x)) , FrameLen, FrameInc);
signs = (tmp1.*tmp2)<0;
diffs = (tmp1 -tmp2)>0.02;
zcr = sum(signs.*diffs, 2);

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

%调整能量门限
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;
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
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;

subplot(311)
plot(x)
axis([1 length(x) -1 1])
ylabel('Speech');
line([x1*FrameInc x1*FrameInc], [-1 1], 'Color', 'red');
line([x2*FrameInc x2*FrameInc], [-1 1], 'Color', 'red');

subplot(312)
plot(amp);
axis([1 length(amp) 0 max(amp)])
ylabel('Energy');
line([x1 x1], [min(amp),max(amp)], 'Color', 'red');
line([x2 x2], [min(amp),max(amp)], 'Color', 'red');

subplot(313)
plot(zcr);
axis([1 length(zcr) 0 max(zcr)])
ylabel('ZCR');
line([x1 x1], [min(zcr),max(zcr)], 'Color', 'red');
line([x2 x2], [min(zcr),max(zcr)], 'Color', 'red');

运行后出现
??? Input argument 'x' is undefined.

Error in ==> D:\我的工具\matlab\work\vad.m
On line 4 ==> x = double(x);
是什么原因呢?
请各位高手帮忙看下谢谢了!!
是不是需要一个信号输入呢 ?

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