how to improve detrending?

Code:

d=load('CU_Ventricular_Tacharrhythmia\cu01m.mat');
noisyECG_withTrend=d.val(1,:);
subplot(2,1,1), plot(noisyECG_withTrend), grid on,
nnoisyECG_withTrend = noisyECG_withTrend';
t = 1:length(noisyECG_withTrend);
[p,s,mu] = polyfit((1:numel(noisyECG_withTrend))',nnoisyECG_withTrend,6)
f_y = polyval(p,(1:numel(noisyECG_withTrend))',[],mu);

ECG_data = nnoisyECG_withTrend - f_y;    % Detrend data

subplot(2,1,2), plot(t,ECG_data); grid on
%ax = axis; 
%axis([ax(1:2) -1.2 1.2])
title('Detrended ECG Signal')
xlabel('Samples'); ylabel('Voltage(mV)')
legend('Detrended ECG Signal')

Code Source: http://www.mathworks.com/help/signal/examples/peak-analysis.html

[Explorer]

Basically, I am trying to remove baseline error so that I can extract features like R to R delay and other intervals.

Answer 1

[Star Strider]

See if this filter does what you want (assuming Fs=256):

Fs = 256;
Fn = Fs/2;
Wp = [1 90]/Fn;
Ws = Wp.*[0.5 1.25];
Rp =  1;
Rs = 20;
[n,Wn] = buttord(Wp,Ws,Rp,Rs);
[b,a] = butter(n,Wn);
[sos,g] = tf2sos(b,a);

figure(1)
freqz(sos, 2048, Fs);

[Explorer]

Yes, it works in removing baseline errors.

[Star Strider]

I was quite definitely hoping it would.

[Evenor]

Can you please comment-in and explain how this filter works? Some of the functions used in it, like 'buttord', do not appear in my MATLAB2014a documentation, so can you elaborate on them (in what toolbox/version they are available and what they do)? Thanks.

[Star Strider]

@Evenor —

My code uses functions from the Signal Processing Toolbox. You need to have it installed in order to run my code. You should be able to run it in R2014a.

[Sibi Ramachandran]

@Star Strider Good morning sir I saw your comments and it helped me to understand the use of these filters. I recently posted a question and I was wondering if you would be able to help me also? Thank you so much!