Here is described a simple process to 'put a voice on a sunbeam' and transmit it over a distance. It is a fascinating example of amplitude modulation of light using sound vibrations. It then describes how the modulated light is detected...

Study the details of sound from characteristics to speed, ultrasound, infrasound, and other aspects of sound waves.

The concept of pitch and frequency is covered in this tutorial. Learn what frequency and pitch are, the difference between infra sound and ultrasonic frequencies, and how pitch is related to the frequency of a sound.