for ii = 1:24 % 7 8 wav分別為背景聲和背景+槍聲，21-24是爆炸聲
    if 8 < ii &&  ii < 21
        continue;
    end
    % 取信號
    file_name = strcat('gun',num2str(ii));
    file_name = strcat(file_name,'.wav');
    fprintf('reading %s...\n',file_name);
    [y,fs] = audioread(file_name);   
    sz = size(y);
    gun = (y(:,1))'; % 單聲道
    % 原信號
    figure(ii);
    p2 = abs(fft(gun)/length(gun));
    % size(gun)
    % size(1:length(gun)/2+1)
    gun_fft = p2(1:length(gun)/2+1);
    gun_fft(2:end-1) = 2*gun_fft(2:end-1);
    f = fs*(0:(length(gun)/2))/length(gun);
    subplot(3,2,1);plot(gun);xlabel('t / s');title('signal');
    subplot(3,2,2);plot(f,gun_fft);title('spectrum');xlabel('frequency / Hz');
    % 短時能量分析
    N = 300; % 窗寬（張克剛）
    inc = 100; % 幀移（張克剛）
    win = hamming(N);
    % frameout: num x N 
    % t: num x 1, centers of frames
    % energy: 1 x num
    [frameout,t,energy]=enframe(y,win,inc);
    t = t';
    % 自適應(yīng)短時能量閾值分割
    %size(energy)
    threshold = min(energy)+0.2*(max(energy)-min(energy));
    processed_energy = energy;
    for i = 1:length(energy)
        processed_energy(i) = 0;
        if energy(i) >= threshold 
            processed_energy(i) = 1;
        end
        %fprintf('%d: %f > %f = %d\n',ii,energy(i),threshold,processed_energy(i));
    end
    subplot(3,2,3); plot(energy,'b');title('energy');
    hold on;plot(threshold*ones(size(energy)),'g');
    subplot(3,2,5); plot(processed_energy);title('binarized energy')
    % 持續(xù)時間分析
    thr = 30; % 持續(xù)采樣點
    cnt = 0;
    for i = 1:length(processed_energy)
        if processed_energy(i) == 1
            if cnt > 0
                cnt = cnt+1; %計數(shù)器累加
            elseif cnt == 0
                cnt = 1; %初始化計數(shù)器
            end
            if i == length(processed_energy) && cnt < thr
                processed_energy((i-cnt):i) = 0;
            end
        elseif processed_energy(i) == 0
            if cnt > 0
                if cnt < thr
                    processed_energy((i-cnt):i) = 0;
                end
            end
            cnt = 0;
        end
        %fprintf('%f, %f\n',i,processed_energy(i));
    end
    
    subplot(3,2,3);hold on;plot(processed_energy*max(energy),'r');hold off;
    subplot(3,2,5);hold on;plot(processed_energy,'r');hold off;
end
function [f,t,eng,zcr]=enframe(x,win,inc)
%ENFRAME split signal up into (overlapping) frames: one per row. [F,T]=(X,WIN,INC)
%
%	F = ENFRAME(X,LEN) splits the vector X(:) up into
%	frames. Each frame is of length LEN and occupies
%	one row of the output matrix. The last few frames of X
%	will be ignored if its length is not divisible by LEN.
%	It is an error if X is shorter than LEN.
%
%	F = ENFRAME(X,LEN,INC) has frames beginning at increments of INC
%	The centre of frame I is X((I-1)*INC+(LEN+1)/2) for I=1,2,...
%	The number of frames is fix((length(X)-LEN+INC)/INC)
%
%	F = ENFRAME(X,WINDOW) or ENFRAME(X,WINDOW,INC) multiplies
%	each frame by WINDOW(:)
%
%   The second output argument, T, gives the time in samples at the centre
%   of each frame. T=i corresponds to the time of sample X(i). 
%
nx=length(x);
nwin=length(win);
if (nwin == 1)
   len = win;
else
   len = nwin;
end
if (nargin < 3)
   inc = len;
end
len = nwin;
nf = fix((nx-len+inc)/inc);
f=zeros(nf,len);
indf= inc*(0:(nf-1)).';
inds = (1:len);
f(:) = x(indf(:,ones(1,len))+inds(ones(nf,1),:));
if (nwin > 1)
    w = win(:)';
    f = f .* w(ones(nf,1),:);
end
t = floor((1+len)/2)+indf;
%fprintf('size of f\n');
szf = size(f);
% ff = f(:).*f(:);
for i = 1:szf(1)
    %ff = f(i,:).*f(i,:)
%     ff = abs(f(i,:));
%     eng(i) = sum(ff);
    eng(i) = 0;
    zcr(i) = 0;
    for j = 1:szf(2)
        eng(i) = eng(i)+abs(f(i,j));
        if j+1 <= szf(2)
            zcr(i) = zcr(i)+abs(sign(f(i,j+1))-sign(f(i,j)));
        end
    end
    zcr(i) = 0.5*zcr(i);
end