speeding up the proccess

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tony karamp 2013-4-25

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https://ww2.mathworks.cn/matlabcentral/answers/73586-speeding-up-the-proccess

关闭： MATLAB Answer Bot 2021-8-20

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hello,

I have a wavfile that I read with 'wavread' and I want to apply some weighting function on each channel. everything is working ok, but it takes almost 2 minutes to through the for loop. Any ideas as to how to speed things up? the sampling frequency fs=32kHz and duration is 10secs.

 [y,fs] = wavread('C:\Desktop\testwavfile')
 y = y';
 t =0:1/fs:length(y)/fs-1/fs;
 t = t';
 gain1 = 0:4/fs:40-4/fs;         %this is level
 gain2 = 20:4/fs:60-4/fs;
 gain3 = 40:-4/fs:0+4/fs;
 t1 = 8*fs;
 slope = (gain2(1)-gain2(t1))/t1;
 con = slope+gain2(1);
 slopeout = (gain1(5*fs)-gain1(t1))/t1;
 conout = slopeout+gain1(5*fs);
 %creates a weighting function
 for iTime = 1:t1
    temp(iTime) = -slope*iTime+con;   %#ok<*SAGROW>
    out(iTime) =  -slopeout*iTime+conout;
 end
 temp(t1+1:length(y)) = 6.5*gain3(t1+1:length(y));
 out(t1+1:length(y)) = 4*gain3(t1+1:length(y));

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Matt Kindig 2013-4-25

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In fact, the for loop doesn't even appear to be necessary. You can define both of them as:

temp(1:t1) = -slope*iTime+con;
out(1:t1) = -slopeout*iTime+conout;

and eliminate the for loop entirely.

tony karamp 2013-4-25

it did the trick. I don't know how I forgot to pre-allocate, I usually do it.

Thanks a bunch!

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