How to deal with this error??

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Good mind 2017-5-4

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评论： Star Strider 2017-5-7

A model of the surface EMG signal is created by filtering a white gaussian noise, using a shaping filter H(f). this filter has low cut-off freq=60hz and high cut-off freq=120hz. this is my code but i don't know how to deal with Undefined function 'designfilt' for input arguments of type 'char'.

clear all;  
    subplot(322);
    load nnoise.m;
    plot(nnoise,'k');
 % design shaping filter
   bpFilt = designfilt('bandpassfir',...
         'CutoffFrequency1',60,'CutoffFrequency2',120, ...
         'SampleRate',2000);
     subplot(323);
     W = filter(bpFilt,nnoise);
     plot(W,'k');title ('EMG');

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Adam 2017-5-4

Do you have the Signal Processing toolbox? If not then you will not have this function.

Good mind 2017-5-4

So what is the solution? how can i get it

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Answer 1

Star Strider 2017-5-4

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https://ww2.mathworks.cn/matlabcentral/answers/338698-how-to-deal-with-this-error#answer_265639

在 MATLAB Online 中打开

The designfilt function was introduced in the R2014a version of the Signal Processing Toolbox.

If you have an earlier version of the Signal Processing Toolbox, this filter will work, since all the functions were introduced prior to R2006a:

Fs = 2000;
notch_frq = [50 60 120 130];
mags = [0 1 0];
devs = [0.05  0.01  0.05];
[n,Wn,beta,ftype] = kaiserord(notch_frq,mags,devs,Fs);
n = n + rem(n,2);
hh = fir1(n,Wn,ftype,kaiser(n+1,beta),'scale');
figure(1)
freqz(hh, 1, 2^17, Fs)

Use the filtfilt function to do the actual filtering of your signal.

See the documentation on the various functions to understand how to use them.

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Good mind 2017-5-5

在 MATLAB Online 中打开

1. white gaussian noise is passed through shaping filter H(f)where H(f)=(fh^4)(f^2)/((f^2)+(fl^2))*((f^2)+(fh^2))^2*, fh and fl change the shape of the spectral function (the goal is create an emg model).

2. the new filtred signal (W)is multiplied by a factor A(this factor is in function of e, f and snr-in) this snr-in is from -5 to 55 in steps of 5db the formula of snr_in in my code is it correct?? because when i type snr-in=55 instead snr-in=(-5:5:55) i get acceptable result

3.noisy ecg = ecg + A*W (ecg is sampled at 360hz from physionet MIT db)

%ecg and noisy ecg clc;

    clear all;
    load m105a.m;
    ecg=m105a;
    subplot(3,2,1);
    plot(ecg); title ('ECG');
    xlabel('samples'); ylabel('magnitude');
    subplot(322);
    load nnoise.m;
    plot(nnoise,'k');
 % using shaping filter
Fs = 2000;
notch_frq = [50 60 120 130];
mags = [0 1 0];
devs = [0.05  0.01  0.05];
[n,Wn,beta,ftype] = kaiserord(notch_frq,mags,devs,Fs);
n = n + rem(n,2);
hh = fir1(n,Wn,ftype,kaiser(n+1,beta),'scale');   
subplot(323);
  W = filtfilt(hh,1,nnoise);
  plot(W,'k');title ('EMG'); 
 % noisy ecg  
    snrin_db=(-5:5:55);                %initial snr in db
    N=length(ecg);
    n=(0:N-1);
    e = sum( ecg(1+n).^2 );
    f = sum( W(1+n).^2 );
    A=sqrt(e./(10.^(snrin_db/10))*f);   %the factor A in function of e and f
    subplot(324);
    ecgnoisy = repmat(ecg(:), 1, length(A)) + repmat(W(:), 1, length(A)) .* repmat(A, numel(W), 1);
    plot(ecgnoisy,'k');title('Noisy signal');

Star Strider 2017-5-5

在 MATLAB Online 中打开

First, since ‘ecg is sampled at 360hz’ your sampling frequency for all your signal processing must be 360 Hz.

Second, your ‘H(f)’ filter does not appear to be coded correctly. In any event, I cannot get a magnitude plot for it that is remotely close to what you want it to do. The FIR filter I designed works correctly.

Third, I have no idea how to interpret 2. in your Comment. This is apparently taken from the ‘Methods’ section of a paper, and has no context for me. I cannot determine if the SNR calculation is correct.

If you get an acceptable result for one value of ‘snrin_db’*, you most likely need to use a loop to calculate all of them:

snrin_db=(-5:5:55);                %initial snr in db
N=length(ecg);
n=(0:N-1);
e = sum( ecg(1+n).^2 );
f = sum( W(1+n).^2 );
for k1 = 1:length(snrin_db)
    A = sqrt(e./(10.^(snrin_db(k1)/10))*f);   %the factor A in function of e and f
    subplot(324);
    ecgnoisy{k1} = repmat(ecg(:), 1, length(A)) + repmat(W(:), 1, length(A)) .* repmat(A, numel(W), 1);
end

I created ‘ecgnoisy’ as a cell array because I do not know its dimensions. The loop should produce a cell array element for each value of ‘snrin_db’.

I cannot run your code, so this is a guess. You may have to experiment to get the result you want.

Good mind 2017-5-7

Mr. Strider I would like to thank you very much. you alerted me to important informations. I hope that everyone will benefit from these discussions, especially beginners.

2^17 is from where?

Star Strider 2017-5-7

As always, it is my pleasure to help.

The ‘2^17’ is the length of the Fast Fourier Transform that freqz uses to compute the transfer function. I apologise for not explaining that earlier.

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