matlab如何解决?Error using ==> conv A and B must be vectors.

matlab如何解决?Error using ==> conv A and B must be vectors.
a=wavread('d.wav'); %读取语音信号的数据,赋给变量x1,这里的文件的全路径和文件名由个人设计
n=length(a);
N=320;
subplot(3,1,1),plot(a);
h=linspace(1,1,N);%形成一个矩形窗,长度为N
En=conv(h,a.*a);%求卷积得其短时能量函数En
subplot(3,1,2),plot(En);
for i=1:n-1
if a(i)>=0
b(i)= 1;
else
b(i) = -1;
end
if a(i+1)>=0
b(i+1)=1;
else
b(i+1)=-1;
end
w(i)=abs(b(i+1)-b(i));
end%求出每相邻两点符号的差值的绝对值
k=1;
j=0;
while (k+N-1) conv
A and B must be vectors.
Error in ==> Untitled2 at 6
En=conv(h,a.*a);%求卷积得其短时能量函数En