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| '''Frequency''' is the inverse of time. In music, specifically it refers to the number of oscillations per unit of time of a vibrating object. Frequency is typically measured in [[Wikipedia:Hertz|hertz]] (Hz), defined as one oscillation per second.
| | Sound is created through air pressure waves--concentric circular regions emanating from the sound-creating object of high pressure and low pressure. In music, the '''frequency''' of a sound is equal to the frequency of the sine wave that represents the same pitch, where the frequency of the sine wave is measured in the number of times per second the object emanating it generates high pressure. Notes with high frequency sound high, and notes with low frequency sound low. Middle C, roughly in the center of the piano, has a frequency of about 255 [[Hertz]] (abbreviated Hz), or oscillations per second, while human hearing range is from about 20 to 20,000 Hz. |
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| A sound's [[pitch]] is associated with the fundamental frequency of its frequency spectrum.
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| == Definition ==
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| By convention, frequency refers to the ''linear'' measure of how "high" or "low" a sound is. That is, a sound that is twice the frequency has twice as many oscillations per second.
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| Usually, absolute frequency in Hz is not of interest to musicians (even in xenharmony), because human beings tend to perceive and memorize [[ratio]]s of frequency instead of absolute frequencies. Because of this, a standard frequency is usually set (by convention, at 440 Hz, which corresponds to the A above middle C), and the frequencies of other notes in the scale are defined by multiplying that base frequency by ratios.
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| Frequency is different from [[pitch]], which is the ''logarithmic'' measure of how "high" or "low" a sound is. Multiplications in frequency translate to additions in pitch; the notes in an equal tuning are equally spaced in pitch.
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| == Overtones ==
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| Frequency ratios that take the form of simple fractions are concordant. This is because of the way notes sound when played on most instruments: the frequency of the note being heard is called the ''fundamental'' frequency (say 440 Hz), but the sound wave also contains other frequencies at integer multiples of the fundamental, called harmonics or overtones: the [[2/1|perfect octave]] at twice the frequency (880 Hz), the [[3/1|third harmonic]] at 3 times the frequency (1320 Hz), and so on. The relative volume of these harmonics determines what sound the instrument has. When the harmonics of two sound waves coincide, the two frequencies are considered concordant. This obviously happens with two sound waves that have the same frequency (i.e. a ratio of [[1/1]]), but also happens with other simple ratios, which include harmonics, but also include ratios like [[3/2]] and [[5/4]]. Because of this, concordance can be considered how much two notes sound like "the same note".
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| | If an instrument generates a single note, when pressure at a given point near the instrument is graphed, the resulting graph<ref>By taking the [[wikipedia:Fourier_transform|Fourier transform]].</ref> is a sum of sine waves of various levels of frequency and amplitude. The frequency of the lowest sine wave is generally perceived as the frequency of a sound, even if this sine wave does not have the largest amplitude. The entire list of frequencies is called the '''frequency spectrum'''. |
| [[Category:Tuning]] | | [[Category:Tuning]] |
| [[Category:Terms]] | | [[Category:Terms]] |
| | Frequency is different from [[pitch]], because multiplications in frequency translate to additions in pitch; successive octaves are equally spaced in pitch, but exponentially increasing in frequency. |
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| | == Intervals == |
| | When two notes have frequencies a:b where b/a is rational, the interval between the two notes is within [[Just intonation]] and denoted b/a. If the two notes have frequency spectra where frequencies are multiples of the lowest frequency (as is the case with most methods of sound production, including the human voice, most instruments, and square/saw/triangle waves) the two notes will sound concordant when played at once. |