move add_sine, lfo_sine to src folder

src/add_sine.m

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+function x = add_sine(amplitude, fundamental, harmonics, fs, duration)
+% ADD_SINE: Additive sine wave synthesis
+
+%CONTRIBUTORS:
+%Benjamin Liou: Original author
+
+% DOCUMENTATION:
+% harmonics should ideally be a 1D matrix of:
+    % overtones: positive integers
+    % undertones: 1/ positive integers
+    % example: [1/2, 1, 2, 3]
+    % NOTE: pitch of the fundamental frequency will still be perceived even
+        % when the fundamental itself is missing. ex. [4,5,6]
+    
+% NOTE: it seems like when MATLAB's built in sound() takes in values,
+    % magnitudes over 1 get distorted.
+    
+    
+    
+    % initialize local variables from input arguments
+    n = fs * duration; % number of samples (length of matrix)
+    
+    % initialize a one dimensional zero matrix to be populated
+    x = zeros(1, n);
+    
+    % populate matrix by adding sine waves
+    for harmonic = harmonics
+        x = x + generate_sine(1, fundamental * harmonic, 0, fs, duration);
+    end
+    
+    % scale to amplitude
+    scalar = max(abs(x));
+    x = x / scalar * amplitude;
+end

src/lfo_sine.m

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+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