public function getChordBitMasks() {
    	$chords = array();
    	$tones = $this->getTones();
    	$doubledTones = array_merge(
    		$tones,
	    	array_map(
	    		function($n){return $n + 12;},
	    		$this->getTones()
	    	)
	    );
    	for ($i=0; $i<count($tones); $i++) {
    		// build a triad on the ith degree
    		$triad = 0;
    		$triad = $triad | (1 << $doubledTones[$i]);
    		$triad = $triad | (1 << $doubledTones[$i + 2]);
    		$triad = $triad | (1 << $doubledTones[$i + 4]);
    		$chords[] = $triad;
    	}
    	return $chords;
    }