Music and Sound

Sound is the most common example of waves that we encounter in our everyday life. A sound wave is caused by the vibration of air molecules in between the source and the listener; this is a clear example of waves transferring energy from one point to another without the transfer of matter.

The speed of sound waves in air is about 300 m/s. The frequency of sound waves is what we denote as the ``pitch'' - the higher the pitch, the higher the frequency. Humans can detect a frequency range from about 20 to 20,000 Hz. The amplitude of a sound wave is related to the energy that the wave carries, and is commonly measured in decibels.

In music, the frequency of the sound wave is denoted by a letter as in, for example, the C major scale in the table below.

 

Table 10.1: C Major Scale

Note	Letter	Frequency (Hz)
do	C	264
re	D	297
me	E	330
fa	F	352
so	G	396
la	A	440
ti	B	495
do	C'	528

 

Note that there is a doubling in frequency in going from C to high C (C') [ie, one octave]. However, we are familiar with the fact that a particular note, such as C, played on a piano, for example, sounds different from the same note played on a guitar. This is due to the presence of various higher frequency harmonics and overtones unique to each musical instrument.