move add_sine, lfo_sine to src folder

src/lfo_sine.m

@@ -0,0 +1,29 @@
+function x = lfo_sine(amplitude, frequency, phase, fs, duration, input)
+% LFO_SINE: modulates an input matrix
+
+% CONTRIBUTORS:
+% Benjamin Liou: Original author
+
+% DOCUMENTATION:
+% frequency is typically below 20Hz (according to wikipedia)
+% fs and duration should be 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 lfo, which will be used to modulate the input
+    lfo = zeros(1, n);
+    
+    % populate lfo matrix
+    for i = 1:n
+        t = i * dt; % time at the i'th sample
+        lfo(i) = amplitude * sin(2 * pi * frequency * t - phase);
+    end
+    
+    % modulate input
+    x = lfo .* input;
+    
+end