bandpass filter in multiple frequencies with a for- if- ifelse loop

Hi everyone!

I have to filter a signal in 5 frequency bands, each with its own range and calculate, for each band, an RMS value. I tried to create a loop, but RMS is overwritten every time a new signal is filtered.

the code:

for freq=1:5

if freq==1

freq_min=0,1

freq_max=0,7

fs=1000

[blow,alow]=butter(2,freq_max/(fs/2));

[bhigh,ahigh]=butter(2,freq_min/(fs/2),'high');

filt_signal=filtfilt((blow,alow,signal);

filt_signal=filtfilt(bhigh,ahigh,filt_signal);

RMS_freq1=rms(filt_signal);

elseif freq==2

freq_min=0,7

freq_max=0,9

fs=1000

[blow,alow]=butter(2,freq_max/(fs/2));

[bhigh,ahigh]=butter(2,freq_min/(fs/2),'high');

filt_signal=filtfilt((blow,alow,signal);

filt_signal=filtfilt(bhigh,ahigh,filt_signal);

RMS_freq2=rms(filt_signal);

ecc..

RMS=[RMS_freq1 RMS_freq2 RMS_freq3 RMS_freq4 RMS_freq5];

end

end

each time the script restarts with a new signal, the RMS array is overwritten.

[Sulaymon Eshkabilov]

Hi,

First of all, the whole structure of your code needs to be re-written by considering the loop.

Second, you should have included the indexes, e.g.:

  freq_min=[0.1; 0.7];
  freq_max=[0.7; 0.9];
  fs=1e3;
for freq=1:5
                        
                            [blow,alow]=butter(2,freq_max(freq)/(fs/2));
                            [bhigh,ahigh]=butter(2,freq_min(freq)/(fs/2),'high');
                            filt_signal(freq,:)=filtfilt(blow, alow,signal);
                            filt_signal(freq,:)=filtfilt(bhigh,ahigh,filt_signal(freq,:));
                            RMS_freq(freq,:)=rms(filt_signal(freq,:));                         
 end
 

Good luck

[Harry Smith]

sorry, but i don't understand what you mean

[Sulaymon Eshkabilov]

You don't need all of these "if .. elseif ... end" conditional statements. A simple [for ... end] loop.

[Harry Smith]

thanks for your help!!

I have 5 frequency bands:

b1: 0.1-0.7 Hz

b2: 0.7-0.9 Hz

b3: 0.9-1.1 Hz

b4 1.1-1.3 Hz

b5: 1.3-1.5 Hz

and i wrote:

freq_min = [0.1; 1.3];

freq_max = [0,7; 1.5];

fs = 1e3;

ecc..

error message: Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.