How to obtain peaks in the y-axis above a reference line in matlab plot

I want to get all the pnts in yaxes for a matlab plot above reference line -70 db

Answer 1

[KSSV]

Let x,y be your data. And reference line is at y = y0. To extract data above y = y0:

idx = y>=y0 ;
x1 = x(idx) ;
y1 = y(idx) ;

[TRISHITA BANERJEE]

This is my script..i want to see peaks of yaxes where it is over the reference line -75.21 db

function [h1, h2, h1_nl, h2_nl] = farina_deconvolution(y1,y2,xinv,CorrFac,ctrl_plot_var ) %% Farina Deconvolution % Convolves the measured signals y1 and y2 with xinv and separates % their linear and non-linear impulse responses

    L1      = length(xinv);
    L2      = length(y1);
    Lin     = L1+L2-1;
    XINV1    = fft(xinv,Lin);
    Y1  = fft(y1,Lin);
    h1_complete = ifft(XINV1.*Y1);

    L1      = length(xinv);
    L2      = length(y2);
    Lin     = L1+L2-1;
    XINV2    = fft(xinv,Lin);
    Y2  = fft(y2,Lin);
    h2_complete = ifft(XINV2.*Y2);

    % extract linear impulse response part
    h1 =  h1_complete  (length(xinv):end)/CorrFac;
    h2 =  h2_complete  (length(xinv):end)/CorrFac;

    % extract non-linear impulse response part    
    h1_nl =  h1_complete  (1:length(xinv)-1)/CorrFac;
    h2_nl =  h2_complete  (1:length(xinv)-1)/CorrFac;

    if ctrl_plot_var
        figure
        subplot(2,1,1);
        plot(20*log10(abs(h1_complete)))
        hline = refline([0 -70]);  % highlight reference thersold at -80 DB
        hline.Color = 'r';
        title('Complete Impulse Responses')
        grid on
        ylabel('h1 \rightarrow dB')
        subplot(2,1,2);
        plot(20*log10(abs(h2_complete)))
        hline = refline([0 -75.21]);  % highlight reference thersold at -80 DB
        hline.Color = 'r';
        ylabel('h2 \rightarrow dB')
        grid on

        figure
        subplot(2,1,1);
        plot(20*log10(abs(h1)))
        hline = refline([0 -75.21]);  % highlight reference thersold at -80 DB
        hline.Color = 'r';
        title('Linear Impulse Responses')
        grid on
        ylabel('h1 \rightarrow dB')
        subplot(2,1,2);
        plot(20*log10(abs(h2)))
        hline = refline([0 -75.21]);  % highlight reference thersold at -80 DB
        hline.Color = 'r';
        ylabel('h2 \rightarrow dB')
        grid on

        figure
        subplot(2,1,1);
        plot(h1)
        title('Linear Impulse Responses')
        grid on
        ylabel('h1 \rightarrow dB')
        subplot(2,1,2);
        plot(h2)
        ylabel('h2 \rightarrow dB')
        grid on

    end
end

Answer 2

[Star Strider]

If you have the Signal Processing Toolbox, use the findpeaks (link) function, and the 'MinPeakHeight' (and perhaps also the 'MinPeakDistance') values set to the appropriate thresholds. For 'MinPeakHeight that would be either -70 if your original data are in dB, or 3.162277660168379e-04 otherwise. You will have to experiment to get the correct 'MinPeakDistance' value.

If you do not, and you have R2017b or later, use the islocalmax (link) function. You will first have to threshold your data to present data only greater than -70 dB. Again, you will have to experiment to get the results you want.