What is sound?
Sound is a sensation in our brains, transmitted from our ears,  caused by vibrations of the air, which in turn, are caused by a vibrating body. Examples of sound sources include a stretched string which has been plucked or hammered, a drum which has been beaten, a vibrating column of air in a pipe, a metal bar or bell which has been struck, or a vibrating paper cone in a loudspeaker.

Sounds can be divided into two kinds, noise and musical sounds. Click on the red button below to hear a noise, and the green button to hear a musical sound.  Musical sounds are usually longer lasting and characterized by a smooth and regular flow, with clearly identifiable qualities of pitch (vibration frequency)  and timbre. Noises consist of a jumble of irregular vibration frequencies, are usually of short duration and continually changing character, they are irregular and impulsive.

Musical sounds have three important characteristics:-

The musical pitch is described in English-speaking countries by a combination of note names and octave numbers. In the most commonly used musical scale (the major scale) there are 7 truly different notes. These then repeat themselves at a higher or lower pitch, but sounding almost the same. These "repeats" are called octaves, because they occur on every eighth note. There are 7  note names, using the first 7 letters of the alphabet, from A to G.  The starting point is "middle C", which is the C note roughly in the middle of a piano keyboard. An upright piano usually has 7 octaves, from the A   3 octaves below the A below middle C, to the A   3 octaves above the A above middle C.

The modern standard for pitch is called "Concert Pitch", and is used by orchestras and musicians playing together to tune their instruments, so everyone is "in tune" with everyone else. At Concert Pitch, the frequency of the A above middle C is 440 cycles per second. All other notes bear a fixed relationship to this A.

The branch of science which deals with sound is called acoustics. This tells us that musical pitch is determined by the frequency of the vibrating body, measured in cycles per second. The next page in this advanced theory series explains the maths behind sound waves. 


TheorySummarySound.htm     03/11/06 13:12            MENU -> Theory ->  Introduction  ->  What is Sound?