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1 Sound waves
Variations in air pressure against the ear drum, and the subsequent physical and neurological processing and interpretation, give rise to the experience called " sound". Most sound that people recognize as " musical" is dominated by periodic or regular vibrations rather than non-periodic ones (called a definite pitch), and we refer to the transmission mechanism as a "sound wave". In a very simple case, the sound of a sine wave, which is considered to be the most basic model of a sound waveform, causes the air pressure to increase and decrease in a regular fashion, and is heard as a very "pure" tone. Pure tones can be produced by tuning forks. The rate at which the air pressure varies governs the frequency of the tone, which is also measured in oscillations per second, or Hertz. Frequency is a primary determinate of the perceived pitch.
A spectrogram of . The bright lines along the bottom are the fundamentals of each note, and the other bright lines are (nearly) harmonic overtones, collectively they are spectra.
Whenever two different pitches are played at the same time, their sound waves interact with each other - the highs and lows in the air pressure reinforce each other to produce a different sound wave. As a result, any given sound wave which is more complicated than a sine wave can, nonetheless, be modelled by many different sine waves of the appropriate frequencies and amplitudes. In humans the hearingHearing is one, the auditory, of the traditional five senses, and refers to the ability to detect sound. In human beings, hearing is performed by the ears, which also perform the function of balance, a sense in itself but not one of the traditional list ( apparatus (composed of the ears and brainFor other articles about other subjects named brain see brain (disambiguation). In the anatomy of animals, the brain or encephalon is the supervisory center of the nervous system. Although the brain is usually cited as the supervisory center of vertebrate) can isolate these tones and hear them distinctly. When two or more tones are played at once, a single variation of air pressure at the ear "contains" the pitches of each, and the ear and/or brain isolate and decode them into distinct tones.
When the original sound sources are perfectly periodic, the noteThis article is about music. For information about money, see banknote. In music, a note is either a unit of fixed pitch that has been given a name, or the graphic representation of that pitch in a notation system, and sometimes its duration, or a specifi consists of several related sine waves (which mathematically add to each other) called the fundamentalA fundamental is something basic and important which other things are built upon. See: Fundamental frequency, a concept in music or phonetics Fundamentalism Fundamental theorem of algebra Fundamental theorem of arithmetic See also Basic Foundation Further and the harmonicIn acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integral multiple of the fundamental frequency. For a sine wave, it is an integral multiple of the frequency of the wave. For example, if the freqs, partials, or overtoneAn overtone is a sinusoidal component of a waveform, of greater frequency than its fundamental frequency. Usually the first overtone is the second harmonic, the second overtone is the third harmonic, etc. Use of the term overtone is generally confined tos. The sounds have harmonicIn acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integral multiple of the fundamental frequency. For a sine wave, it is an integral multiple of the frequency of the wave. For example, if the freq spectra. The lowest frequency present is the fundamental, and is the frequency that the entire wave vibrates at. The overtones vibrate faster than the fundamental, but must vibrate at integer multiples of the fundamental frequency in order for the total wave to be exactly the same each cycle. Real instruments are close to periodic, but the frequencies of the overtones are slightly imperfect, so the shape of the wave changes slightly over time.
