anchor.diff:  
       // function for generating a random fiddle tune in a random key
       var random_fiddle_tune = function() {
  -        // pick a key randomly
  -        var key = Math.floor(Math.random()*12);
  +        // determine the key of the fiddle tune
  +        // http://stackoverflow.com/questions/15839169/how-to-get-value-of-selected-radio-button
  +        var key = $("input[name=key_choice]:checked").val();
  +        // pick a random key if they checked the random button
  +        if (key === -1) {
  +            key = Math.floor(Math.random() * 12);
  +        };
           // generate the tune
           var tune = fiddletune(key);
           // play the tune at 75 beats per minute
  
positive.code:             // console.log("start and end times for " + tune[0][note] + ": " + (0.75*note) + " and " + (0.75*(note+1)));
              MIDI.noteOn(0, tune[0][note] + 60, 127, (60/tempo)*tune[1][note][0] + offset);
              MIDI.noteOff(0, tune[0][note] + 60, (60/tempo)*tune[1][note][1] + offset);
          };
      }
  
      var possibleRhythms = [[[0, 1]], [[0, 0.5], [0.5, 0.75], [0.75, 1]], [[0, 
       0.25], [0.25, 0.5], [0.5, 0.625], [0.625, 0.75], [0.75, 1]], [[0,
        0.25], [0.25, 0.5], [0.5, 0.75], [0.75, 1]], [[0, 0.5], [0.5, 
       1]], [[0, 0.25], [0.25, 0.5], [0.5, 1]]];
      </script>
negative.code: 	<h1>HACC</h1>
      <h2>Human-Aided Computer Composition</h2>
  	<div class="row-fluid">
          <section id="about">
              <div class="row">
                  <div class="col-md-6 col-md-offset-3">
                      <!-- http://getbootstrap.com/javascript/#collapse-example-accordion -->
                      <div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true">
                        <div class="panel panel-default">
                          <div class="panel-heading" role="tab" id="headingOne">
                            <h4 class="panel-title">
                              <a data-toggle="collapse" data-parent="#accordion" href="#whatsthis" aria-expanded="false" aria-controls="whatsthis">
                                What's This?
                              </a>
                            </h4>
                          </div>
                          <div id="whatsthis" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingOne">
                            <div class="panel-body">
                              Human-Aided Computer Composition (HACC) was an exploratory project I started in 2010 to see whether computers could compose music effectively. Over the course of 21 months, the programs I wrote (in <a href="http://www.wolfram.com/mathematica/">Mathematica</a>) were able to produce sixty-second violin duets, string quartets, and fiddle tunes. Below is the result of rewriting my fiddle tune code in Javascript. Select a key by clicking on the appropriate radio button, click "Generate Fiddle Tune", and (thanks in part to the <a href="http://mudcu.be/midi-js/">Midi.js</a> library) my program will start playing a newly-composed Irish reel.
                              <br><br>
                              I plan to port my violin duet and string quartet code to Javascript soon. Until then, have fun making reels!
                            </div>
                          </div>
                        </div>
                      </div>
                  </div>
              </div>
          </section>
  		<section id="music">
              <div class="col-md-6 col-md-offset-3">
                  <div class="form-group">
                    <div class="col-sm-2 col-sm-offset-5 center">
                      <label class="control-label">Key</label>
                    </div>
                    <br>
                    <div class="col-sm-12">
                      <div class="row">
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="0">C Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="1">C# Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="2">D Major
                          </label>
                        </div>
                      </div>
                      <div class="row">
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="3">D# Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="4">E Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="5">F Major
                          </label>
                        </div>
                      </div>
                      <div class="row">
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="6">F# Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="7">G Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="8">G# Major
                          </label>
                        </div>
                      </div>
                      <div class="row">
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="9">A Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="10">A# Major
                          </label>
                        </div>
                        <div class="col-sm-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="11">B Major
                          </label>
                        </div>
                      </div>
                      <div class="row">
                        <div class="col-sm-4 col-sm-offset-4">
                          <label class="radio-inline">
                            <input type="radio" name="key_choice" value="-1" checked>Random
                          </label>
                        </div>
                      </div>
                    </div>
                  </div>
                  <div class="col-md-6 col-md-offset-3 center">
                    <br>
      			  <button class="btn btn-primary" onclick="random_fiddle_tune()">Generate Fiddle Tune</button>
                  </div>
                  <!-- <button class="btn btn-primary" onclick="MIDI.Player.pause()">Pause</button> -->
              </div>
  		</section>
              <div class="col-md-6 col-md-offset-3">
  