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函数：

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 返回输入序列x的上下包络线，作为其解析信号的大小。              %% x的解析信号是利用希尔伯特实现的离散傅里叶变换得到的。           %% 这个函数首先移除x的均值，然后在计算包络线之后再把它加回来。      %% 如果x是一个矩阵，那么包络线对x的每一列都是独立的。             %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[yupper,ylower] = envelope(x)%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 返回用解析信号的大小确定的x的包络线。                        %% 解析信号通过使用长度为fl的Hilbert FIR滤波器对x进行滤波来计算。 %% 如果只指定两个参数，则使用此语法。                           %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[yupper,ylower] = envelope(x,fl,'analytic')%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 返回x的上、下均方根包络。包络是使用长度wl样本的滑动窗口确定的。  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[yupper,ylower] = envelope(x,wl,'rms')%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 返回x的上峰和下峰包络线。                                  %% 包络线由至少np个样本分离的局部最大值上的样条插值确定。         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%[yupper,ylower] = envelope(x,np,'peak')%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 在没有输出参数的情况下，绘制信号及其上下包络线。               %% 该语法接受以前语法中的任何输入参数。                         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%envelope(___)

例1： [up,lo] = envelope(q)

% 信号生成t = 0:1/2000:2-1/2000;q = chirp(t-2,4,1/2,6,'quadratic',100,'convex').*exp(-4*(t-1).^2);plot(t,q)% 包络线绘制[up,lo] = envelope(q);hold onplot(t,up,t,lo,'linewidth',1.5)legend('q','up','lo')hold off

% 信号生成t = 0:1/1000:3;q1 = sin(2*pi*7*t).*exp(-t/2);q2 = chirp(t,30,2,5).*exp(-(2*t-3).^2)+2;q = [q1;q2]';plot(t,q)% 包络线绘制[up,lo] = envelope(q,100,'analytic');hold onplot(t,up,'-',t,lo,'--')hold off

例3：不同参数的包络线区别

% 信号生成t = 0.5:-1/100:-2.49;z = airy(t*10).*exp(-t.^2);plot(z)% 无参数figureenvelope(z)% 参数：analytic,使用50-tap Hilbert filter计算信号的包络线figureenvelope(z,50,'analytic')% 参数：rms，使用40个样本的移动窗口来计算信号的RMS包络figureenvelope(z,40,'rms')% 参数：peak，确定峰包络，在被至少10个样本分隔的局部极大值上使用非结点条件的样条插值。figureenvelope(z,10,'peak')

参考文献：

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