Merge pull request #27 from ltcptgeneral/alex

Alex

README.md

@@ -57,10 +57,10 @@ where LOW, MED, HIGH are user-selected variables of any value.
  
  ## Useful websites
  
- - https://learningsynths.ableton.com
+ - [Learning Synths](https://learningsynths.ableton.com)
- - https://learningsynths.ableton.com/en/playground
+ - [Learning Synths Playground](https://learningsynths.ableton.com/en/playground)
- - https://blog.demofox.org/diy-synthesizer/
+ - [DIY Synthesisers](https://blog.demofox.org/diy-synthesizer/)
- - http://portaudio.com/
+ - [Port Audio (audio I/O library)](http://portaudio.com/)
- - https://ccrma.stanford.edu/software/stk/
+ - [Synthesis ToolKit in C++](https://ccrma.stanford.edu/software/stk/)
- - https://cycling74.com/products/max
+ - [Max](https://cycling74.com/products/max)
- - http://msp.ucsd.edu/software.html
+ - [Software by Miller Puckette](http://msp.ucsd.edu/software.html)

src/generate_heartbeat.m

@@ -0,0 +1,46 @@
+function x = generate_heartbeat(amplitude, frequency, phase, fs, duration, duty)
+% GENERATE_SINE: returns a matrix of sampled heart monitor wave
+
+% CONTRIBUTORS:
+% Alex Nguyen: Original Author
+% Conner Hsu: Reviewed Code and Assisted in polishing
+
+% DOCUMENTATION:
+% phase shift is in number of periods
+% fs is the sampling frequency: how many sample points per second
+% duration is time in seconds
+% duty cycle should be a number between 0 and 0.5.
+    % duty of 0 or less would return 0 for all sample points
+    % duty of 0.5 or less would return a heartbeat signal since there would be
+        % equal amount of space within 1 period to have the right and left sides be equal
+    % duty of greater than 0.5 but less than 1 would return a slope starting at that duty i.e.
+        % the left side but leaving little room to the right side
+    % duty of between 1 and 2 would give a sawtooth wave in the +amplitude.
+    % duty greater than 2 would return 0 for all sample points
+   
+
+    % 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
+    x = zeros(1, n);
+    
+    % populate the matrix
+    for i = 1:n
+        t = i * dt; % time at the i'th sample
+        st = mod(frequency * t - phase, 1);
+
+        if (duty-(duty / 2) < st && st < duty)
+            slope = amplitude / duty;
+            intercept = -0.5 * amplitude;
+            x(i) = slope * st + intercept;
+        elseif (duty < st && st < duty+(duty / 2)) 
+            slope = amplitude / duty;
+            intercept = -amplitude;
+            x(i) = slope * st + (1.5 * intercept);
+        else
+            x(i) = 0;
+    end
+end