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Asked: 2026-05-21T09:58:49+00:00

Greetings All I went back and used resample (from the signal processing toolbox) and

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Greetings All

I went back and used resample (from the signal processing toolbox) and repmat, but I’m noticing that on some of the values the rows aren’t the same as the sample rate, see image link below. notice the top image value for rows says 1000 and the bottom image says rows = 1008. This happens when I change the values of resample and repmat (freq_new) but only for certain values. How can I fix this correctly? I could just delete everything after 1000 but I’m not sure if this is a bug or just the way resample/repmat works. PS: using matlab/octave

http://dl.dropbox.com/u/6576402/questions/rows_different.png

Here’s the test code I used to test this

%resample_repmat signal
clear all, clf
Fs = 1000; % Sampling rate
Ts = 1/Fs; %sampling interval
t=0:Ts:1-Ts; %sampling period

freq_orig=1;
y=sin(2*pi*t*freq_orig)'; %gives a short wave

freq_new=9;
y2=resample(y,1,freq_new); %resample matrix
y3=repmat (y2,freq_new,1); %replicate matrix

[r_orig,c_orig] = size(y) %get orig number of rows and cols
[r_new,c_new] = size(y3) %get new number of rows and cols

subplot(2,1,1),plot(y),title('Orginal signal')
title(['rows=',num2str(r_orig),' cols=',num2str(c_orig)])
subplot(2,1,2),plot(y3),title('New signal')
title(['rows=',num2str(r_new),' cols=',num2str(c_new)])
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1 Answer

  1. Editorial Team

    Since your original signal is 1000 samples long, resampling it with a period 9 times shorter would give you 111.11111… samples in one cycle. Matlab rounds this number up to 112. Think about it. If your cycles were 111 samples long, your complete wave would be 999 samples long. Because it’s 112 samples long, when you put nine of them together they produce a 1008-samples-long signal. There is no way to make it 1000, because you’re dealing with discrete times. The code is right, it does what it’s supposed to. There is physically no way to fit precisely 9 identical cycles of anything into 1000 discrete samples. I hope this helps.

    Alternatively, you can try first repeating your initial wave nine times and then resampling it. Your cycles would not be identical, but they would fit nicely into the 1000 samples.

    I hope this helps = )

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