MATLAB: How to read a period of wav file in matlab

digital signal processing

I need to read a wav file with cycle, period by period. I need help in this task.

Best Answer

If you use wavread, you can use an argument to read a range of samples. You would have to increment that in a loop.

The same is true of audioread.m

   [y,fs] = wavread(filename,[start end]);

If have the DSP System Toolbox, then the task is easier with System objects. See dsp.AudioFileReader and set the SamplesPerFrame property.

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MATLAB: Split file.wav

elis - the answer you included was to split the wav file into 1 second chunks. You want to do something different and split the data into 5Mb files. In order to do this (and it will give a rough estimate only), you will need to know some information about your wav file: the number of channels, the number of bits per sample, and the sampling frequency (I'm guessing a bit here based on what I've read online). Luckily, you can use audioinfo to get that information. So we'll do this by an example. Let's create a sample wav file using the handel.mat data

>> handelData = load('handel.mat');

which has a sampling frequency of 8192 and 73113 samples (single channel) and is roughly 8.9 seconds long. Let's increase this to ten minutes (by repeating) and write to file

>> tenMinuteData = repmat(handelData.y, 68, 1);
>> audiowrite('handel.wav', tenMinuteData, handelData.Fs);

which creates a ~10Mb file. Using audioinfo gives us

>> handelAudioInfo = audioinfo('handel.wav')
handelAudioInfo = 
             Filename: '/Users/.../handel.wav'
    CompressionMethod: 'Uncompressed'
          NumChannels: 1
           SampleRate: 8192
         TotalSamples: 4971684
             Duration: 606.89501953125
                Title: []
              Comment: []
               Artist: []
        BitsPerSample: 16

Now we are going to split this file into roughly 5Mb chunks which means we need to calculate the number of samples that we write to each of these files. If we (safely?) assume that audio data (excluding wav file header and other information) size of the wav file can be estimated by

SampleRate * NumChannels * (BitsPerSample / 8) * Duration

then a 5Mb data size corresponds to

>> numSamplesPer5MbFile = 5000000 / (handelAudioInfo.NumChannels * handelAudioInfo.BitsPerSample/8)
numSamplesPer5MbFile =
     2500000

which seems valid since there are ~5000000 samples in the ten minute file. So we can try the following

handelAudioInfo = audioinfo('handel.wav');
numSamplesPer5MbFile = 5000000 / (handelAudioInfo.NumChannels * handelAudioInfo.BitsPerSample/8);
[y,Fs] = audioread('handel.wav');
n = length(y);
atBlock = 1;
for k = 1:numSamplesPer5MbFile:n
    audioBlock = y(k:min(k + numSamplesPer5MbFile - 1, n), :);
    audiowrite(sprintf('handel%03d.wav', atBlock), audioBlock, Fs);
    atBlock = atBlock + 1;
end

For me, this created two new files

-rw-r--r--  1 staff  5000044  9 Apr 13:54 handel001.wav
-rw-r--r--  1 staff  4943412  9 Apr 13:54 handel002.wav

each roughly 5Mb in size.

MATLAB: How to plot WAV file

If this is the output of wavread, then see if you have two channels in y

[y,fs] = wavread(filename);

If y is two-channels, Nx2, then just plot one:

    y = y(:,1);
    dt = 1/fs;
    t = 0:dt:(length(y)*dt)-dt;
    plot(t,y); xlabel('Seconds'); ylabel('Amplitude');
    figure
    plot(psd(spectrum.periodogram,y,'Fs',fs,'NFFT',length(y)));

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MATLAB: Split file.wav

MATLAB: How to plot WAV file

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