How to add a vertical line in a plot that corresponds to a maximum?

Hello, everyone!

I would like to add a vertical line corresponding to the maximum value of the graph attached (and displaying its value). Basically, I need a line that is 'x= fundamental frequency' . I know that similar questions are already answered in the forum, but could not find something working for me. Below I have attached the code and the audio file, accompanied with the last graph that I want to add the line to. Thank you very much in advance!

close all;
clear all;
clc;

%______________________________________________________

[y, Fs] = audioread('A1-sound.wav');

t=linspace(0,length(y)/Fs, length(y));
Fn = Fs/2;

L = length(y);    
Y = fft(y);

phase2 = abs(Y/L);
phase1 = phase2(1:L/2+1);
phase1(2:end-1) = 2*phase1(2:end-1);

F = Fs*(0:(L/2))/L;

%_______________________________Frequencies Distribution

figure;
subplot(2,1,1);
plot(F,phase1);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');

%__________________________________________________Focus

idx =  F >= 0 & F <= 1000;         %Focusing 0-1000 Hz
zoomX = F(idx);
zoomY = phase1(idx);

subplot(2,1,2);
plot(zoomX, zoomY);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');

%________________________________________Fundamental Frequency

[maxValue, f1] = max(Y);


idx2 =  F >= 80 & F <= 120;        %Focusing 80-120 Hz  
zoomX2 = F(idx2);
zoomY2 = phase1(idx2);

figure;
plot(zoomX2, zoomY2);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');

Answer 1

[Star Strider]

Changing part of your code to draw the vertical lines, and the text label in figure(2):

%__________________________________________________Focus
idx =  F >= 0 & F <= 1000;         %Focusing 0-1000 Hz
zoomX = F(idx);
zoomY = phase1(idx);
subplot(2,1,2);
plot(zoomX, zoomY);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');
[pks1,locs1] = findpeaks(zoomY, 'MinPeakProminence',0.002, 'MinPeakDistance',100);      % Identify Prominent Peaks ...
hold on
ylv = ylim;
plot([1;1]*zoomX(locs1), ylv(:)*ones(size(pks1')))                                      % ... & Plot Vertical Lines Through Them
hold off
%________________________________________Fundamental Frequency
[maxValue, f1] = max(Y);
idx2 =  F >= 80 & F <= 120;        %Focusing 80-120 Hz  
zoomX2 = F(idx2);
zoomY2 = phase1(idx2);
figure;
plot(zoomX2, zoomY2);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');
[pks2,locs2] = max(zoomY2);                                                             % Identify Prominent Peak ...
hold on
plot([1;1]*zoomX2(locs2)', ylv(:)*ones(size(pks2')))                                    % ... & Plot Vertical Line Through It
text(zoomX2(locs2), pks2/2, sprintf('\\leftarrow %.1f Hz = Fundamental Frequency',zoomX2(locs2)), 'HorizontalAlignment','left')

I wasn’t certain if you also wanted the vertical lines in the lower subplot, so I used findpeaks to add them as well. The peak in figure(2) kist needs max, since ther is only one peak.

Experiment to get the result you want.

[Petros Tsitouras]

Amazing! Just what I needed. Thank you very much Star Strider!! Just for the sake of curiosity, is it possible to draw the line up to the maximum value of the peak instead of infinity? Something like: line([fundamental fundamental], [0 maxValue])?

[Star Strider]

As always, my pleasure!

Yes.

To get vertical lines from 0 to the maximum of each peak, the plot calls change to:

plot([1;1]*zoomX(locs1), [pks1 zeros(size(pks1))]')                                     % ... & Plot Vertical Lines Through Them

and

plot([1;1]*zoomX2(locs2)', [pks2;0]*ones(size(pks2')))                                  % ... & Plot Vertical Lines Through It

respectively.

The rest of my code is unchanged.

[Petros Tsitouras]

Great! Thanks a lot once more!

[Star Strider]

As always, my pleasure!