Resampling of time signal in MATLAB

Question

I want to resample my signal with to new time. Currently the sampling time of my signal is 0.01s , and the size of my signal and time array is 1*90001 .

I am trying to use resample(x,p,q) in MATLAB, but I am a little bit confused.

Can somebody suggest the right way to use this function and how to resample my data to rate of 0.02s instead of 0.01s ?

Code - this is how I am trying to use resample , with example data.

t = [0:0.03:1];
x = sin(4*pi*t);
y = resample(x, 1, 2);
ty = resample(t,1,2);

figure (1);
stem(ty, y, 'r*');
hold on;
stem(t,x,'b')
hold off

Updated Code :

t = [0 2 3 7 8 9 10 11 12 17 18 19 20 24 25 26 27 28 29 31 32 33 35 37 41 ];
A = [0 0 1 2 3 5.2 0 -1.4 0 2 2.7 2 2.3 6 7.3 0 0 -8.6 0 1 1 2.5 3 4.8 2];
plot(t,A)
% Tx = min(diff(t));
Tx = 1:0.1:25;
B = interp1(t,A,Tx); %re-make example data to have decimal points on the x-axis
 y = resample(B, 2, 1); 
 T = 0.05;
 Ty = T / (2 / 1); 
 ty = (0:length(y)-1)*Ty;
% A = interp1(t,ref,t2);
% A = ref;
figure 
plot(Tx,B,'b')
hold on
plot(ty,y,'r')
plot(t,A,'g')
hold off

Answer 1

your original signal is sampled with uniform sampling interval of 10 ms and you want to decrease sampling down to 20 ms. Why don't you just take every second datapoint of your original signal?

y = x(1:2:end);
ty = t(1:2:end);

UPDATE

for non regularly spaced datasets it is possible to use function resample as it is shown here: https://au.mathworks.com/help/signal/ref/resample.html#bungoxs

you can try

fs = 1/0.02;
[y, ty] = resample(x, t, fs, 1, 2)

Answer 2

First of all you do not need to resample time line. It is much easier to define time sampling interval variable or sampling frequency variable: T = 0.03; Fs = 1/T; T = 0.03; Fs = 1/T;

So, x resampling you perform right way: y = resample(x, 1, 2); .

But the new time line must be reconstructed via adjusted sampling interval: Ty = T / (1 / 2); ty = (0:length(y)-1)*Ty; Ty = T / (1 / 2); ty = (0:length(y)-1)*Ty;

The resample function is suitable only for uniformly time distributed data points. If your original points are non-uniformly distributed, you need:

1. Interpolate your x signal to the uniform time line with the smallest sampling interval from the original time line: Tx = min(diff(t)); . See for example interp1 function.
2. Resample your interpolated uniformly time distributed (sampled) signal to the new sampling interval ( resample function).

Answer 3

There is another way to resample in a lower frequency your data. Use this code :

fs=1/(timesignal(2)-timesignal(1)); %for example 48000Hz
fs_resampled=100; % [Hz] example goal value 
t_original = [0:1/fs:(1/fs*(length(signal)-1))];%current time signal
t_resampled = [0:1/fs_resampled:max(t_original)];%new time signal
Signal_resampled = interp1(t_original,signal,t_resampled,'spline');

I hope that's what you wanted. Greetings