Create lfo_square

src/LFO/lfo_square

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+function x = lfo_square(amplitude, frequency, phase, fs, duration, input)
+% LFO_SQUARE: modulates an input matrix to a square
+
+% CONTRIBUTORS:
+% Aleksandra Desens: Author
+
+% DOCUMENTATION:
+% phase shift is in number of periods
+% fs is the sampling frequency - below 20 Hz
+% duration - same as input
+
+    % initialize local variables from input arguments
+    n = fs * duration; % number of samples (length of matrix)
+    dt = 1 / fs; % sampling period: time between two sample points
+    
+    % initialize a one dimensional zero matrix to be populated
+    lfo = zeros(1, n);
+    
+    % populate the matrix
+    for i = 1:n
+        
+        t = i * dt;
+        duty = 0.5;  % duty of 0.5 generates a square wave
+
+        st = mod((frequency * t - phase), 1);
+
+        if (st < duty) 
+            lfo(i) = amplitude;
+        else
+            lfo(i) = -amplitude;
+
+    end
+
+    % modulate input
+    x = lfo .* input;
+
+end