1.   Ultrasonic waves are at a higher pitch than the human ear can hear.

2.   And it is analog circuitry in the CD player that turns the digital code back into an electronic speaker signal that a human ear can hear.

3.   As the ear hears birds chirping, separate cells respond to each frequency while others compute the direction and intensity of the sound.

4.   But not every ear hears these sounds the same.

5.   So, you sing the bass line long enough that the ear hears it and gets used to it.

6.   Technically it was proficient, but even untrained ears could hear there were no dynamics and no emotion in the playing.

7.   The ears hear more, ranging from the comforting call of the invisible whippoorwill to the rustling of something in the deep woods.

8.   This meant one ear heard the noise just billionths of a second before the other.