Splitting an audio file in Matlab

Question

I'm trying to split an audio file into 30 millisecond disjoint intervals using Matlab. I have the following code at the moment:

clear all
close all

% load the audio file and get its sampling rate
[y, fs] = audioread('JFK_ES156.wav');

for m = 1 : 6000
    [t(m), fs] = audioread('JFK_ES156.wav', [(m*(0.03)*fs) ((m+1)*(0.03)*fs)]);
end

But the problem is that I get the following error:

In an assignment  A(I) = B, the number of elements in B and I
must be the same.

Error in splitting (line 12)
    [t(m), fs] = audioread('JFK_ES156.wav', [(m*(0.03)*fs)
    ((m+1)*(0.03)*fs)]);

I don't see why there's a mismatch in the number of elements in B and I and how to solve this. How can I get past this error? Or is there just an easier way to split the audio file (maybe another function I don't know about or something)?

score 3 · Answer 1 · answered Apr 28 '15 at 12:00

I think the easiest way to split audio is to just load it and use the vec2mat function. so you would have something like this;

[X,Fs] = audioread('JFK_ES156.wav');

%Calculate how many samples you need to capture 30ms of audio
matSize = Fs*0.3;

%Pay attention to that apostrophe. Makes sure samples are stored in columns
%rather than rows.
output = vec2mat(x,matSize)';

%You can now have your audio split up into the different columns of your matrix. 
%You can call them by using the column calling command for matrices.

%Plot first 30ms of audio 
plot(output(:,1));

%You can join the audio back together using this command. 
output = output(:);

Hope that helps. Another good thing about this method is that it keeps all your data in one place!

Edit : One thing I thought of, you may get a problem with this depending on your vector size. But I think vec2mat actually zeroPads your vector. Not a big thing, but if you're moving back and forth between the two, then it might be a good idea to have another variable that stores the original length of your signal.

vec2mat does zero padding. It is also part of communications System toolbox. — Navan, Apr 28 '15 at 14:13

score 2 · Accepted Answer · answered Apr 28 '15 at 01:40

You should just use the variable y and reshape it to form your split audio. For example,

chunk_size = fs*0.03;
y_chunks = reshape(y, chunk_size, 6000);

That will give you a matrix with each column a 30 ms chunk. This code will also be faster than reading small segments from file in a loop.

As hiandbaii suggested you could also use cell array. Make sure you clear your existing variables before that. Not clearing the array t is probably the reason you got the error "Cell contents assignment to a non-cell array object."

Your original error is because you cannot assign a vector with scalar indexing. That is, 'm' is a scalar, but your audioread call is returning a vector. This is what the error says about mismatch in size of I and B. You could also fix that by making t a 2-D array and use an assignment like

[t(m,:), fs] =

score 1 · Answer 3 · answered Apr 27 '15 at 21:41

1

It appears that each 30 ms segment is not equal to one sample. That would be the only case where your code works. i.e. 0.03*fs != 1.

You could try using cells instead.. i.e. replace t(m) with t{m}

answered Apr 27 '15 at 21:41

hiandbaii

1,276
8
14

I get the following error when I try that: "Cell contents assignment to a non-cell array object." – Essam Apr 27 '15 at 22:35

Splitting an audio file in Matlab

3 Answers3