Add lfo_sawtooth function

src/lfo_sawtooth.m

@@ -0,0 +1,37 @@
+function x = lfo_sawtooth(amplitude, frequency, phase, fs, duration, input)
+% LFO_SAWTOOTH: modulates an input matrix to a sawtooth parameter
+
+% CONTRIBUTORS:
+% Ben Zhang: Function Author
+
+% DOCUMENTATION:
+% frequency is below 20Hz for people to hear the sound
+% 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);
+    period = 1 / frequency; % period of the wave
+    slope = 2 * amplitude / period; % the incline slope from start to amplitude
+     
+    % populate lfo matrix
+    for i = 1:n
+        t = i * dt; % time at the i'th sample
+        st = mod(frequency * t - phase, 1); % Progression through cycle
+        %part before the straght vertical line
+        if(st < period /2) 
+            lfo(i) = amplitude * slope;
+        %part after the straght vertical line
+        else
+            lfo(i) = amplitude * (slope - 1);
+    
+    end
+    
+    % modulate input
+    x = lfo .* input;
+    
+end