Inacoustics, abeat is aninterference pattern between twosounds of slightly differentfrequencies,perceived as a periodic variation involume, the rate of which is thedifference of the two frequencies.
Withtuning instruments that can produce sustained tones, beats can be readily recognized. Tuning two tones to aunison will present a peculiar effect: when the two tones are close in pitch but not identical, the difference in frequency generates the beating. The volume varies as in atremolo while the sounds alternately interfere constructively and destructively. As the two tones gradually approach unison, the beating slows down and may become so slow as to be imperceptible. As the two tones get further apart, their beat frequency begins approaching the range of human pitch perception,[1] the beating starts to sound like a note, and acombination tone is produced.
This phenomenon is best known in acoustics or music, though it can be found in any linear system:
"According to thelaw of superposition, two tones sounding simultaneously are superimposed in a very simple way: one adds their amplitudes".[2]
If a graph is drawn to show thefunction corresponding to the total sound of twostrings, it can be seen that maxima and minima are no longer constant (as when a pure note is played), but change over time: when the two waves are nearly 180 degreesout of phase the maxima of one wave cancel the minima of the other, whereas when they are nearly in phase their maxima sum up, raising the perceived volume.
It can be proven (with the help of asum-to-product trigonometric identity) that the sum of two unit-amplitudesine waves can be expressed as a carrier wave of frequencyf1 +f2/2 whoseamplitude is modulated by anenvelope wave of frequencyf1 -f2/2:[3]
Since every other burst in the modulation pattern is inverted, each peak is replaced by a trough and vice versa. The envelope is perceived to havetwice the frequency of the modulating cosine, which means theaudible beat frequency (if it is in the audible range) is:[4]
"Monaural beats are when there is only one tone that pulses on and off in a specific pattern. With only one tone (as opposed to two tones with binaural beats), your brain has a much easier time adjusting and there is no need to balance separate tones.
Monaural beats are combined into one sound before they actually reach the human ear, as opposed to formulated in part by the brain itself, which occurs with a binaural beat.
This means that monaural beats can be used effectively via either headphones or speakers. It also means that those without two ears can listen to and receive the benefits." - Ebonie Allard[5]
A binaural beat is anauditory illusion that can occur when two sine waves of different frequencies are presented to a listener dichotically (one in each ear).
For example, if a 530 Hz puretone is presented to a subject's right ear, while a 520 Hz pure tone is presented to the subject's left ear, the listener will hear beating at a rate of 10 Hz, just as if the two tones were presented monaurally, but the beating will also have an element of lateral motion.
Binaural-beat perception originates in theinferior colliculus of themidbrain and thesuperior olivary complex of thebrainstem, whereauditory signals from each ear are integrated and precipitateelectrical impulses alongneural pathways through thereticular formation up the midbrain to thethalamus,auditory cortex, and other cortical regions.[6]
According to a 2023 systematic review, studies have investigated some of the claimed positive effects in the areas of cognitive processing. Affective states like anxiety, mood, pain perception, meditation, relaxation, mind wandering, and creativity were studied, but it was determined that the techniques were not comparable and the results were inconclusive. Out of fourteen studies reviewed, five reported results in line with thebrainwave entrainment hypothesis, eight studies reported contradictory, and one had mixed results. The authors recommend standardization in study approaches for future studies so results may be more effectively compared.[7]
Musicians commonly use interference beats objectively to checktuning at theunison,perfect fifth, or other simple harmonic intervals.[8] Piano andorgan tuners use a method involving counting beats, aiming at a particular number for a specific interval.
Manypipe organs contain"céleste" stops that intentionally produce beating by having two sets of pipes which are slightly out of tune with each other, producing an undulating effect.
ThecomposerAlvin Lucier has written many pieces that feature interference beats as their main focus. Italian composerGiacinto Scelsi, whose style is grounded on microtonal oscillations of unisons, extensively explored the textural effects of interference beats, particularly in his late works such as the violin solosXnoybis (1964) andL'âme ailée / L'âme ouverte (1973), which feature them prominently (Scelsi treated and notated each string of the instrument as a separate part to make his violin solos effectively quartets of one-strings, where different strings of the violin may be simultaneously playing the same note with microtonal shifts, so that the interference patterns are generated). ComposerPhill Niblock's music is entirely based on beating caused by microtonal differences.[9] Computer engineer Toso Pankovski invented a method based on auditory interference beating to screen participants in online auditory studies for headphones and dichotic context (whether the stereo channels are mixed or completely separated).[10]
Amateur radio enthusiasts use the terms "zero-beating" or "zero-beat" for precisely tuning to a desiredcarrier wave frequency by manually reducing the number of interference beats,[11] fundamentally the same tuning process used by musicians.
Learning materials related toBeat (acoustics) at Wikiversity| Acoustical engineering | ||
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| Psychoacoustics | ||
| Audio frequency andpitch | ||
| Acousticians | ||
| Related topics | ||
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| Perfect Consonances | ||
| Imperfect Consonances | ||
| Dissonances | ||
