How can I resample 50Hz signal to 30Hz?

I have a accelerometer data whose sample rate is 50Hz. Now, I want to resample this data to 30Hz. How can I do it? I have tried functions like resample, interp and decimate but all of them require the factor to be an integer which is not in this case. Is there any function which can work with non integer factor?

Answer 1

[Star Strider]

It’s always best to upsample rather than downsample because it’s easier to design filters for them.

If you must, use the Signal Processing Toolbox resample funciton:

S50 = ...;                                                  % Signal Sampled At 50 Hz
S30 = resample(S50, 3, 5);                                  % Resampled Signal At 30 Hz

Use resample rather than interp. The resample function incorporates a FIR anti-aliasing filter.

[Bijay Ratna Shakya]

Hi Strider! Thanks for the suggestion. It seems fine for the 50Hz sample but I also have data with sample rate 6.25Hz. How can I resample this to 30Hz? Trying the same code is giving error. Please suggest.

[Star Strider]

My pleasure.

To resample your 6.25 Hz signal to 30 Hz, you need a rat:

S6 = ...;                                                   % Signal Sampled At 6.25 Hz
Fsa =  6.25;                                                % Actual Sampling Frequency
Fsd = 30;                                                   % Desired Sampliing Frequency
[N,D] = rat(Fsd/Fsa);                                       % Rational Fraction Approximation
Check = [Fsd/Fsa, N/D]                                      % Approximation Accuracy Check (Delete)
S30 = resample(S6, N, D);                                   % Resampled Signal

I did something similar to this yesterday in: convert the time domain signal into frequency domain signal, Comment#21.

[Bijay Ratna Shakya]

Thank you so much for the help. It worked fine for me.TC!!

[Star Strider]

As always, my pleasure!

[sania urooj]

Hey! I have tried this code too but the sample remain same , it just divide (10 sec) duration ecg signal to 2.5 seconds keepin the 2500 sample as same as before resampling. Did you get it ? please tell me how to resolve it.

Answer 2

[Aishwarya Ghosh]

Is there any way we can do sampling rate conversion(SRC) by an integer factor I/D without using the function 'resample'. Like theoretically, SRC is just upsampling the signal by a factor I, then using a filter(low pass) and then downsampling it by a factor D. Can anyone suggest me how to do that without using the inbuit function 'resample'? Thanks!

[Matteo Meli]

Try y = downsample(x,n)