Sound with frequencies higher than the range of human hearing is called ultrasonic while sound with frequencies lower than the range of human hearing is called infrasonic.
The loudness of a sound is associated with the amplitude of its wave. Noise is random, non-repeating sound. A musical sound is a repeating wave.
Most musical sounds are composed of a lowest frequency, called the fundamental frequency and a superposition of other frequencies called harmonics or overtones. The pitch of a sound refers to its frequency or its fundamental frequency. The additional harmonics that are present, and their relative strengths, give a sound its distinctive quality, or timbre, or voice. These additional harmonics let us distinguish a piano from a harpsichord or a French horn from an oboe.
The frequency of two notes an octave apart differ by a factor of two. Two notes are pleasing to the ear when their frequencies are the ratio of small whole numbers. The notes on a piano, as part of an equally tempered scale, are compromises between pure diatonic scales so that music pieces written in different keys can be played without retuning the piano.
Two sounds with close frequencies will interfer constructively and destructively with time, causing the volume that is heard to increase and decrease with a frequency equal to the difference in their frequencies. This is known as beats.
The Doppler effect refers to the change in pitch heard if the sound source or listener is moving.
A large amplitude shock wave is produced when a source moves faster than the speed of sound. When this shock wave strikes the ground, a sonic boom is heard or felt.