Pure tone: Difference between revisions

In [[psychoacoustics]] and [[signal processing]], a '''pure tone''' is a sound or a [[signal]] with a [[sinusoidal]] [[waveform]]; that is, a [[sine]] [[wave]] of anyconstant [[frequency]], [[phase-shift]], and [[amplitude]].<ref>[[ANSI S1.1-1994|ANSI S1.1-1994 Acoustical Terminology]]</ref>

Pure tones have been used by 19th century physicists like [[Georg Ohm]] and [[Hermann von Helmholtz]] to support theories asserting that the ear functions in a way equivalent to a [[Fourier analysis|Fourier frequency analysis]].<ref>{{cite book |last1=von Helmholtz |first1=Hermann L. F. |last2=Ellis |first2=Alexander J. |title=On the sensations of tone as a physiological basis for the theory of music |date=1875 |publisher=Longmans, Green, and Co. |location=London, UK |url=https://archive.org/stream/onsensationston00helmgoog#page/n2/mode/2up}}</ref><ref>{{cite journal |last1=Ohm |first1=Georg |title=Ueber die Definition des Tones, nebst daran geknupfter Theorie der Sirene und ahnlicher tonbildenden Vorrichtungen |journal=Poggendor's Annalen der Physik und Chemie |date=1843 |volume=59 |pages=513–565}}</ref> In [[Ohm's acoustic law]], later further elaborated by Helmholtz, [[Musicalmusical tone|musical tones]]s are perceived as a set of pure tones. The percept of [[Pitch (music)|pitch]] depends on the frequency of the most prominent tone, and the phases of the individual components is discarded. This theory has often been blamed for creating a confusion between pitch, frequency and pure tones.<ref>{{cite book | title = Foundations of Modern Auditory Theory | editor = Jerry V. Tobias | publisher = Academic Press | volume = 1 | author = W. Dixon Ward | chapter = Musical Perception |year = 1970 | page = 438}}</ref>

Unlike [[Musicalmusical tone|musical tones]]s that are composed of the sum of a number of harmonically related sinusoidal components, pure tones only contain one such sinusoidal waveform. When presented in isolation, and when its frequency pertains to a certain range, pure tones give rise to a single pitch percept, which can be characterized by its frequency. In this situation, the instantaneous phase of the pure tone varies linearly with time. If a pure tone gives rise to a constant, steady-state percept, then it can be concluded that its phase does not influence this percept. However, when multiple pure tones are presented at once, like in musical tones, their relative phase plays a role in the resulting percept. In such a situation, the perceived pitch is not determined by the frequency of any individual component, but by the frequency relationship between these components (see [[missing fundamental]]).<gallery>

File:Middle C, or 262 hertz, on a virtual oscilloscope.png|Pure tone [[Oscilloscope|oscillogram]] of middle C (262  Hz). (Scale: 1 square is equal to 1 [[millisecond]])

File:C3 131 Hz oscillogram.png|Pure tone for C3, an [[octave]] below middle C. The frequency is half that of [[C (musical note)|middle C]] (131  Hz).

File:C5 523 Hz oscillogram.png|Pure tone oscillogram of C5, an [[octave]] above middle C. The frequency is twice that of middle C (523  Hz).