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

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Harry Smith on 17 May 2021
Commented: Harry Smith on 17 May 2021
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.
##### 4 CommentsShowHide 3 older comments
Harry Smith on 17 May 2021
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.

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