We begin with a discussion of the essential nature of sound as pressure waves in air, discussing matters such as the speed of sound, harmonic frequencies, loudness, standing waves, and the Doppler effect. We then apply these basic principles to understand the nature of music, and why different musical instruments sound different. Also discussed are the various aspects of music, including beat, pitch, melody, timbre, etc, and the differences between woodwind, percussion, brass, and string instruments. Recommended prelistening is Episode 24: Vibrations and Waves