how can I plot frequency spectrum and impulse response with hold on?

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studentmatlaber 2021-11-30

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评论： Star Strider 2021-12-15

采纳的回答： Star Strider

在 MATLAB Online 中打开

Hi. I passed the signals in the time domain to the frequency domain and plotted the spectrum:

        L = length(Ti{i,j});                                                        % Length Of Time & Signal Vectors
        Ts = mean(diff(Tt));                                                        % Sampling Interval
        Fs{i,j} = 1/Ts;                                                             % Sampling Frequency
        Fn = Fs{i,j}/2;                                                             % Nyquist Frequency
        X = fftshift(fft(x)/L);                                                  
        Fv2 = linspace(-Fn, Fn, L);
        plot(Fv2, abs(X));
        grid;
        xlabel('Frequency (Hz)');
        ylabel('Amplitude');
        

Then I designed a low pass filter and plotted the impulse response of the filter:

        [n, fo, ao, w] = firpmord ([0.09 0.7], [1 0], [0.001 0.01], Fs{i,j});
        b = firpm (n, fo, ao, w);
        filtered_signal{i,j} = filtfilt(b,1,nonoffset{i,j});
        fvtool(b,1)
        

I want to plot the graph of the signal in the frequency domain and the graph of the impulse response. But I need to convert frequency to normalized frequency and convert amplitude to dB. How can I do these? I would be very happy if you show me a way.

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Star Strider 2021-11-30

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Use freqz instead of fvtool to plot the transfer function of the filter, and specify the sampling frequency of the signal in the freqz call so that the frequency is plotted as actual frequency, not normalised frequency. It will be necessary to plot the phase angle of ‘X’ as well as the amplitude in the appropriate plots, since freqz produces subplot plots. Note that only the ‘positive’ half of ‘X’ will need to be plotted because the freqz transfer function only depicts the ‘positive’ half of its Fourier transform.

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studentmatlaber 2021-12-15

在 MATLAB Online 中打开

"to divide the entire signal magnitude by the maximum magnitude" It didn't come to life as a code in my head.

    f_radsec = Fv2 * pi / Fn; %Hz to rad/sample
    fvtool(b,1) %impulse response
    hold on
    ydb = mag2db(abs(X)); %amplitude to magnitude (dB)
    plot(f_radsec, ydb);