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Psychoacoustics

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Psychoacousticsis the branch ofpsychophysicsinvolving the scientific study of theperceptionofsoundby the humanauditory system.It is the branch of science studying thepsychologicalresponses associated with sound includingnoise,speech,andmusic.Psychoacoustics is an interdisciplinary field including psychology,acoustics,electronic engineering, physics, biology, physiology, and computer science.[1]

Background

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Hearing is not a purely mechanical phenomenon ofwave propagation,but is also a sensory and perceptual event. When a person hears something, that something arrives at theearas a mechanical sound wave traveling through the air, but within the ear it is transformed into neuralaction potentials.These nerve pulses then travel to the brain where they are perceived. Hence, in many problems in acoustics, such as foraudio processing,it is advantageous to take into account not just the mechanics of the environment, but also the fact that both the ear and the brain are involved in a person's listening experience.[citation needed]

Theinner ear,for example, does significantsignal processingin converting soundwaveformsinto neural stimuli, this processing renders certain differences between waveforms imperceptible.[2]Data compressiontechniques, such asMP3,make use of this fact.[3]In addition, the ear has a nonlinear response to sounds of different intensity levels; this nonlinear response is calledloudness.Telephone networksand audionoise reductionsystems make use of this fact by nonlinearly compressing data samples before transmission and then expanding them for playback.[4]Another effect of the ear's nonlinear response is that sounds that are close in frequency produce phantom beat notes, orintermodulationdistortion products.[5]

The termpsychoacousticsalso arises in discussions about cognitive psychology and the effects that personal expectations, prejudices, and predispositions may have on listeners' relative evaluations and comparisons of sonic aesthetics and acuity and on listeners' varying determinations about the relative qualities of various musical instruments and performers. The expression that one "hears what one wants (or expects) to hear" may pertain in such discussions.[citation needed]

Limits of perception

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Anequal-loudness contour.Note peak sensitivity around2–4 kHz,in the middle of thevoice frequency band.

The human ear can nominally hear sounds in the range20 to 20000Hz.The upper limit tends to decrease with age; most adults are unable to hear above16000Hz.The lowest frequency that has been identified as a musical tone is 12 Hz under ideal laboratory conditions.[6]Tones between 4 and 16 Hz can be perceived via the body'ssense of touch.

Human perception of audio signal time separation has been measured to be less than 10 microseconds. This does not mean that frequencies above100 kHzare audible, but that time discrimination is not directly coupled with frequency range.[7][8]

Frequency resolution of the ear is about 3.6 Hz within the octave of1000–2000 HzThat is, changes in pitch larger than 3.6 Hz can be perceived in a clinical setting.[6]However, even smaller pitch differences can be perceived through other means. For example, the interference of two pitches can often be heard as a repetitive variation in the volume of the tone. This amplitude modulation occurs with a frequency equal to the difference in frequencies of the two tones and is known asbeating.

Thesemitonescale used in Western musical notation is not a linear frequency scale butlogarithmic.Other scales have been derived directly from experiments on human hearing perception, such as themel scaleandBark scale(these are used in studying perception, but not usually in musical composition), and these are approximately logarithmic in frequency at the high-frequency end, but nearly linear at the low-frequency end.

The intensity range of audible sounds is enormous. Human eardrums are sensitive to variations in sound pressure and can detect pressure changes from as small as a fewmicropascals(μPa) to greater than100kPa.For this reason,sound pressure levelis also measured logarithmically, with all pressures referenced to20 μPa(or1.97385×10−10atm). The lower limit of audibility is therefore defined as0dB,but the upper limit is not as clearly defined. The upper limit is more a question of the limit where the ear will be physically harmed or with the potential to causenoise-induced hearing loss.

A more rigorous exploration of the lower limits of audibility determines that the minimum threshold at which a sound can be heard is frequency dependent. By measuring this minimum intensity for testing tones of various frequencies, a frequency-dependentabsolute threshold of hearing(ATH) curve may be derived. Typically, the ear shows a peak of sensitivity (i.e., its lowest ATH) between1–5 kHz,though the threshold changes with age, with older ears showing decreased sensitivity above 2 kHz.[9]

The ATH is the lowest of theequal-loudness contours.Equal-loudness contours indicate the sound pressure level (dB SPL), over the range of audible frequencies, that are perceived as being of equal loudness. Equal-loudness contours were first measured by Fletcher and Munson atBell Labsin 1933 using pure tones reproduced via headphones, and the data they collected are calledFletcher–Munson curves.Because subjective loudness was difficult to measure, the Fletcher–Munson curves were averaged over many subjects.

Robinson and Dadson refined the process in 1956 to obtain a new set of equal-loudness curves for a frontal sound source measured in ananechoic chamber.The Robinson-Dadson curves were standardized asISO226 in 1986. In 2003,ISO 226was revised asequal-loudness contourusing data collected from 12 international studies.

Sound localization

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Main article:Sound localization

Sound localizationis the process of determining the location of a sound source. The brain utilizes subtle differences in loudness, tone and timing between the two ears to allow us to localize sound sources.[10]Localization can be described in terms of three-dimensional position: theazimuthor horizontal angle, thezenithor vertical angle, and the distance (for static sounds) or velocity (for moving sounds).[11]Humans, as mostfour-legged animals,are adept at detecting direction in the horizontal, but less so in the vertical directions due to the ears being placed symmetrically. Some species ofowlshave their ears placed asymmetrically and can detect sound in all three planes, an adaption to hunt small mammals in the dark.[12]

Masking effects

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Main article:Auditory masking
Audio masking graph

Suppose a listener can hear a given acoustical signal under silent conditions. When a signal is playing while another sound is being played (a masker), the signal has to be stronger for the listener to hear it. The masker does not need to have the frequency components of the original signal for masking to happen. A masked signal can be heard even though it is weaker than the masker. Masking happens when a signal and a masker are played together—for instance, when one person whispers while another person shouts—and the listener doesn't hear the weaker signal as it has been masked by the louder masker. Masking can also happen to a signal before a masker starts or after a masker stops. For example, a single sudden loud clap sound can make sounds inaudible that immediately precede or follow. The effects ofbackward maskingis weaker than forward masking. The masking effect has been widely studied in psychoacoustical research. One can change the level of the masker and measure the threshold, then create a diagram of a psychophysical tuning curve that will reveal similar features. Masking effects are also used in lossy audio encoding, such asMP3.

Missing fundamental

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Main article:Missing fundamental

When presented with aharmonic seriesof frequencies in the relationship 2f,3f,4f,5f,etc. (wherefis a specific frequency), humans tend to perceive that the pitch isf.An audible example can be found on YouTube.[13]

Software

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Perceptual audio coding uses psychoacoustics-based algorithms.

The psychoacoustic model provides for high qualitylossy signal compressionby describing which parts of a given digital audio signal can be removed (or aggressively compressed) safely—that is, without significant losses in the (consciously) perceived quality of the sound.

It can explain how a sharp clap of the hands might seem painfully loud in a quiet library but is hardly noticeable after a car backfires on a busy, urban street. This provides great benefit to the overall compression ratio, and psychoacoustic analysis routinely leads to compressed music files that are one-tenth to one-twelfth the size of high-quality masters, but with discernibly less proportional quality loss. Such compression is a feature of nearly all modern lossy audio compression formats. Some of these formats includeDolby Digital(AC-3),MP3,Opus,Ogg Vorbis,AAC,WMA,MPEG-1 Layer II(used fordigital audio broadcastingin several countries), andATRAC,the compression used inMiniDiscand someWalkmanmodels.

Psychoacoustics is based heavily onhuman anatomy,especially the ear's limitations in perceiving sound as outlined previously. To summarize, these limitations are:

A compression algorithm can assign a lower priority to sounds outside the range of human hearing. By carefully shifting bits away from the unimportant components and toward the important ones, the algorithm ensures that the sounds a listener is most likely to perceive are most accurately represented.

Music

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Psychoacoustics includes topics and studies that are relevant tomusic psychologyandmusic therapy.Theorists such asBenjamin Boretzconsider some of the results of psychoacoustics to be meaningful only in a musical context.[14]

Irv Teibel'sEnvironments seriesLPs (1969–79) are an early example of commercially available sounds released expressly for enhancing psychological abilities.[15]

Applied psychoacoustics

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Psychoacoustic model

Psychoacoustics has long enjoyed a symbiotic relationship withcomputer science.Internet pioneersJ. C. R. LickliderandBob Taylorboth completed graduate-level work in psychoacoustics, whileBBN Technologiesoriginally specialized in consulting on acoustics issues before it began building the firstpacket-switched network.

Licklider wrote a paper entitled "A duplex theory of pitch perception".[16]

Psychoacoustics is applied within many fields of software development, where developers map proven and experimental mathematical patterns in digital signal processing. Many audio compression codecs such asMP3andOpususe a psychoacoustic model to increase compression ratios. The success ofconventional audio systemsfor the reproduction of music in theatres and homes can be attributed to psychoacoustics[17]and psychoacoustic considerations gave rise to novel audio systems, such as psychoacousticsound field synthesis.[18]Furthermore, scientists have experimented with limited success in creating new acoustic weapons, which emit frequencies that may impair, harm, or kill.[19]Psychoacoustics are also leveraged insonificationto make multiple independent data dimensions audible and easily interpretable.[20]This enables auditory guidance without the need for spatial audio and insonificationcomputer games[21]and other applications, such asdroneflying andimage-guided surgery.[22]It is also applied today within music, where musicians and artists continue to create new auditory experiences by masking unwanted frequencies of instruments, causing other frequencies to be enhanced. Yet another application is in the design of small or lower-quality loudspeakers, which can use the phenomenon ofmissing fundamentalsto give the effect of bass notes at lower frequencies than the loudspeakers are physically able to produce (see references).

Automobile manufacturers engineer their engines and even doors to have a certain sound.[23]

See also

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Psychoacoustic topics

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References

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Notes

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  1. ^Ballou, Glen (2012-11-12).Handbook for Sound Engineers(Fourth ed.).Taylor & Francis.p. 43.ISBN9781136122538.
  2. ^Christopher J. Plack (2005).The Sense of Hearing.Routledge.ISBN978-0-8058-4884-7.
  3. ^Lars Ahlzen; Clarence Song (2003).The Sound Blaster Live! Book.No Starch Press.ISBN978-1-886411-73-9.
  4. ^Rudolf F. Graf (1999).Modern dictionary of electronics.Newnes.ISBN978-0-7506-9866-5.
  5. ^Jack Katz; Robert F. Burkard & Larry Medwetsky (2002).Handbook of Clinical Audiology.Lippincott Williams & Wilkins.ISBN978-0-683-30765-8.
  6. ^abOlson, Harry F.(1967).Music, Physics and Engineering.Dover Publications. pp. 248–251.ISBN978-0-486-21769-7.
  7. ^Kuncher, Milind (August 2007)."Audibility of temporal smearing and time misalignment of acoustic signals"(PDF).boson.physics.sc.edu.Archived(PDF)from the original on 14 July 2014.
  8. ^Robjohns, Hugh (August 2016)."MQA Time-domain Accuracy & Digital Audio Quality".soundonsound.Sound On Sound.Archivedfrom the original on 10 March 2023.
  9. ^Fastl, Hugo; Zwicker, Eberhard (2006).Psychoacoustics: Facts and Models.Springer. pp. 21–22.ISBN978-3-540-23159-2.
  10. ^Thompson, Daniel M. Understanding Audio: Getting the Most out of Your Project or Professional Recording Studio. Boston, MA: Berklee, 2005. Print.
  11. ^Roads, Curtis. The Computer Music Tutorial. Cambridge, MA: MIT, 2007. Print.
  12. ^Lewis, D.P. (2007): Owl ears and hearing. Owl Pages [Online]. Available:http:// owlpages /articles.php?section=Owl+Physiology&title=Hearing[2011, April 5]
  13. ^Acoustic, Musical (9 March 2015)."Missing Fundamental".YouTube.Archivedfrom the original on 2021-12-20.Retrieved19 August2019.
  14. ^Sterne, Jonathan (2003).The Audible Past: Cultural Origins of Sound Reproduction.Durham: Duke University Press.ISBN9780822330134.
  15. ^Cummings, Jim."Irv Teibel died this week: Creator of 1970s" Environments "LPs".Earth Ear.Retrieved18 November2015.
  16. ^Licklider, J. C. R. (January 1951)."A Duplex Theory of Pitch Perception"(PDF).The Journal of the Acoustical Society of America.23(1): 147.Bibcode:1951ASAJ...23..147L.doi:10.1121/1.1917296.Archived(PDF)from the original on 2016-09-02.
  17. ^Ziemer, Tim (2020). "Conventional Stereophonic Sound".Psychoacoustic Music Sound Field Synthesis.Current Research in Systematic Musicology. Vol. 7. Cham: Springer. pp. 171–202.doi:10.1007/978-3-030-23033-3_7.ISBN978-3-030-23033-3.S2CID201142606.
  18. ^Ziemer, Tim (2020).Psychoacoustic Music Sound Field Synthesis.Current Research in Systematic Musicology. Vol. 7. Cham: Springer.doi:10.1007/978-3-030-23033-3.ISBN978-3-030-23032-6.ISSN2196-6974.S2CID201136171.
  19. ^"Acoustic-Energy Research Hits Sour Note".Archived fromthe originalon 2010-07-19.Retrieved2010-02-06.
  20. ^Ziemer, Tim; Schultheis, Holger; Black, David; Kikinis, Ron (2018). "Psychoacoustical Interactive Sonification for Short Range Navigation".Acta Acustica United with Acustica.104(6): 1075–1093.doi:10.3813/AAA.919273.S2CID125466508.
  21. ^CURAT."Games and Training for Minimally Invasive Surgery".CURAT.University of Bremen.Retrieved15 July2020.
  22. ^Ziemer, Tim; Nuchprayoon, Nuttawut; Schultheis, Holger (2019). "Psychoacoustic Sonification as User Interface for Human-Machine Interaction".International Journal of Informatics Society.12(1).arXiv:1912.08609.doi:10.13140/RG.2.2.14342.11848.
  23. ^Tarmy, James (5 August 2014)."Mercedes Doors Have a Signature Sound: Here's How".Bloomberg Business.Retrieved10 August2020.

Sources

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