From a2dea29304c8003026c6c660f462a5f821857a3c Mon Sep 17 00:00:00 2001
From: "paul.ewing" <paul.ewing@ecam.fr>
Date: Mon, 18 Mar 2024 09:33:25 +0100
Subject: [PATCH] added frequencySpectrum.m

---
 frequencySpectrum.m | 64 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 frequencySpectrum.m

diff --git a/frequencySpectrum.m b/frequencySpectrum.m
new file mode 100644
index 0000000..ea63086
--- /dev/null
+++ b/frequencySpectrum.m
@@ -0,0 +1,64 @@
+function power = frequencySpectrum(signal, fs, resolution)
+%%%%%%%%%%%%%%%%%%
+%function power = frequencySpectrum(signal, fs, pad)
+%
+% Task: Display the power spectrum (lin and log scale) of a given signal
+%
+% Input:
+%    - signal: the input signal to process
+%    - fs: the sampling rate in Hz
+%    - resolution: frequency resolution in Hz, signal will be padded with zeros if necessary
+%
+% Output: 
+%    - power: the power spectrum
+%    
+%
+% Guillaume Gibert, guillaume.gibert@ecam.fr
+% 15/03/2024
+%%%%%%%%%%%%%%%%%%
+
+n = length(signal);          % number of samples
+current_resolution = fs / n;
+if (resolution < current_resolution)
+    n_original = n;
+    n = fs / resolution;
+    signal = [signal zeros(1, n-n_original)];
+end
+
+%~ if (pad)
+    %~ n_original = n;
+    %~ n = 2^(nextpow2(n));
+    %~ signal = [signal zeros(1, n-n_original)];
+%~ end
+
+y = fft(signal, n);% compute DFT of input signal
+power = abs(y).^2/n;    % power of the DFT
+
+[val, ind] = max(power); % find the mx value of DFT and its index
+
+% plots
+figure;
+
+subplot(1,3,1) % time plot 
+t=0:1/fs:(n-1)/fs; % time range
+plot(t, signal)
+xticks(0:0.1*fs:n*fs);
+xticklabels(0:0.1:n/fs);
+xlabel('Time (s)');
+ylabel('Amplitude (a.u.)');
+title('Time');
+
+subplot(1,3,2) % linear frequency plot
+f = (0:n-1)*(fs/n);     % frequency range
+plot(f,power, 'b*'); hold on;
+plot(f,power, 'r');
+xlim([5, 20]);
+xlabel('Frequency (Hz)')
+ylabel('Power (a.u.)')
+title('Linear Frequency');
+
+subplot(1,3,3) % log frequency plot
+plot(f,10*log10(power/power(ind)));
+xlabel('Frequency (Hz)')
+ylabel('Power (dB)')
+title('Log Frequency');
\ No newline at end of file