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               <div class="wrapper">
   <div id="chord-diagram"></div>
  <audio id="jam-track" src="https://myguitarpal.com/wp-content/uploads/2014/09/12-Bar-Blues-in-A-Version-1.mp3" controls></audio>
  <br>

  <label>Beat: </label>
  <div class="data" id="beat"></div>

  <label>Measure: </label>
  <div class="data" id="measure"></div>
   
  <label>Section: </label>
  <div class="data" id="section"></div>

  <label>Chord: </label>
  <div class="data" id="chord"></div>

  <div id="chord-progression"></div>
</div>
            
          
!
            
              .wrapper {
  max-width: 400px;
}

#chord-progression {
  margin-top: 20px;
  padding-top: 20px;
  border-top: 1px solid lightgray;
}

.section {
  margin-bottom: 20px;
  display: none;
}

.measure {
  width: 25%;
  display: inline-block;
}

.m-line {
  float: right;
  width: 10px;
}

audio {
  width: 100%;
}

.data {
  display: inline;
  margin-right: 10px;
}

label {
  font-weight: bold;
}
            
          
!
            
              (function(){
  // beats per minute
  var BPM = 117;

  // beats per second
  var BPS = 60 / BPM;

  // measures used for count in
  var measuresCount = 1;

  // time the track starts
  var offsetSeconds = 0.2;

  // time signature
  var timeSigTop = 4;
  var timeSigBottom = 4;

  var sectionOne = ['A7', 'A7', 'A7', 'A7', 'D7', 'D7', 'A7', 'A7', 'E7', 'D7', 'A7', 'A7'];
  var sectionTwo = ['A7', 'A7', 'A7', 'A7', 'D7', 'D7', 'A7', 'A7', 'E7', 'D7', 'A7', 'A7', 'A7', 'A7', 'A7', 'A7', 'A7', 'A7'];

  var chordProgression = [
    sectionOne,
    sectionOne,
    sectionOne,
    sectionTwo
  ];
  
  var currentSection;
  var currentChord;
  var cleanMeasure;
  var measureBeat;

  // every time the ontimeupdate event fires, run the jam station
  var audio = document.getElementById('jam-track');
  audio.ontimeupdate = function() {
    jamStation();
  };

  function jamStation() {
    var beat = (audio.currentTime - offsetSeconds + BPS) / BPS; 
    var measure = (beat - 1) / timeSigTop;

    // round down for beat and measure
    var cleanBeat = Math.floor(beat);
    cleanMeasure = Math.floor(measure);

    // find the current beat within the measure
    measureBeat = ((cleanBeat - 1) % timeSigTop) + 1;

    // set the current chord and section.  s = section, m = measure 
    if (cleanMeasure > 0) {
      // find the current section
      var count = 0;
			var br = false;
      
      for(var s = 0; s < chordProgression.length; s++) {
        for(var m = 0; m < chordProgression[s].length; m++) {
          count++;
          if (cleanMeasure == count) {
            currentSection = s + 1;
            currentChord = chordProgression[s][m];
            br = true;
            break;
          }
        }
        if (br === true) {
          break;
        }
      }
    } else {
      currentSection = null;
      currentChord = null;
    }

    // display the jam staion and it's data
    renderJamStation();
  }

  function renderJamStation() {
    // show the beat within the measure, not overall
    document.getElementById('beat').innerHTML = measureBeat;

    // show the current measure, but only if the jam track is past the count in measures
    var measureElem = document.getElementById('measure');

    // only show the current measure if it's > 0
    if (cleanMeasure > 0) {
      measureElem.innerHTML = cleanMeasure;
    } else {
      measureElem.innerHTML = '';
    }

    // show the section number
    document.getElementById('section').innerHTML = currentSection;
    // show the current chord name
    document.getElementById('chord').innerHTML = currentChord;

    // hide all sections before displaying only the section we want to see
    var allSections = document.getElementsByClassName('section');
    for (var i = 0; i < allSections.length; i++) {
      allSections[i].style.display = 'none';
    }

    // show the currently playing section
    if (currentSection !== null) {
      document.getElementById('section-' + currentSection).style.display = 'block';
    } else {
      allSections[0].style.display = 'block';
    }

    // style the current chord in the chord progression
    if (cleanMeasure > 0) {
      // style all measures black
      var measures = document.getElementsByClassName('measure');
      for (i = 0; i < measures.length; i++) {
         measures[i].style.color = 'black';
      }
      // style current measure red
      document.getElementById('measure-' + cleanMeasure).style.color = 'red';
    }
  }

  // take the chordProgression array and render the HTML
  function renderChordProgression() {
    var progression = document.getElementById('chord-progression');

    // make the sections
    for (s = 0; s < chordProgression.length; s++) {
      progression.innerHTML += '<div class="section" id="section-' + (s + 1) + '"></div>';
    }

    var count = 0;

    for (var s = 0; s < chordProgression.length; s++) {
      for (var m = 0; m < chordProgression[s].length; m++) {
        count++;
        var section = document.getElementById('section-' + (s + 1));
        section.innerHTML += '<div class="measure" id="measure-' + count + '">' 
                          + chordProgression[s][m] 
                          + '<div class="m-line">|</div></div>';
      }
    }
  }

  renderChordProgression();
  jamStation();
}());
            
          
!
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