To change the recording frequency of biomechanical data from 60 Hz to 100 Hz

Hello,

Would you please help me to find answers to the following questions?

I have biomechanical variables recorded at 60 Hz and I want to upsample them to 100 Hz. The reason is that I need 100 frames per second as a standard for other mathematical calculations. Using mathematical operations, I have to calculate new variables. I am wondering 1) is there a special type of upsampling for biomechanical data? 2) what is the most accurate method for upsampling my data? 3) if it is possible to apply mathematical operations at 60 Hz and then apply upsampling (to new variables resulted from mathematical operations at 60 Hz)?

Somebody introduced me this solution (here the sampling frequency of comvx is 60 Hz and I want to resample it at 100 Hz):

weight= 60  % to normalize data to weight
phaz=100
for i=1:length(comvx);
for j=1:phaz;
comvx_ir(1,:)=1nterp1([1:length (comvx)],comvx(i),[1:(length(comvx)-1/(phaz-1):length(comvx)],'cubic')/weight;
end 
end

But I receive the following message:

Error: Unexpected MATLAB expression.

I am a beginner and do not have a good knowledge regarding MATLAB solutions. I really appreciate your assistance.

[Walter Roberson]

Avoid putting a space between a function name and the ( to indicate its arguments.

This is especially important when you are within [] list building or {} cell building, as spaces are significant for those

Answer 1

[Star Strider]

I would advise against using interp1. Instead use the Signal Processing Toolbox resample fucntion, since it uses an anti-aliasing filter. This is important if you want to do signal processing with your data. (It may also be more straightforward.)

[Vahid Esmaeili]

Thank you so much for your answer. It is easier to use the resample function than interp1. As I am a beginner and still not confident, would you please check the following lines:

originalFs = 60;
desiredFs = 100;
[p,q] = rat(desiredFs / originalFs)
comvx_100Hz = resample(comvx,p,q); 

I used this link for that program to increase the frequency of 'comvx' from 60 Hz to 100 Hz: https://www.mathworks.com/help/signal/examples/resampling-uniformly-sampled-signals.html.

I decided to first increase the sampling rate of all biomechanical variables to 100 Hz and then apply mathematical calculations.

Would you please confirm that the 'resample function' could be applied for analog signals (like signals of electromyography (EMG))?

Have a nice time

[Star Strider]

My pleasure!

It is not necessary to use the rat function (although you can if you want to). It is sufficient just to define:

p = desiredFs;
q = originalFs;

Please understand that unless it is sound coming out of your soundcard output, nothing in a computer is ‘analog’. Everything is represented as individual numbers. EMG and other physiological signals that are originally continuous (analog) are passed through an anti-aliasing Bessel filter, then sampled with an analog-to-digital converter (ADC) and then stored as individual numbers at corresponding time points (also digital).

The resample function will work correctly on all signals input to it, regardless of what they were originally. I have frequently used resample on physiological signals, most often to be certain that the output sample times were constant and consistent, since this is necessary for all signal processing applications. Higher original sampling frequencies are always better.

[Vahid Esmaeili]

Dear Star Strider,

Thank you so much for your favors.

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

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