Psychoacoustics

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Psychoacoustics is the branch of psychophysics involving the scientific study of the perception of sound by the human auditory system. It is the branch of science studying the psychological responses associated with sound including noise, speech, and music. Psychoacoustics is an interdisciplinary field including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science. [1]

Contents

Background

Hearing is not a purely mechanical phenomenon of wave propagation, but is also a sensory and perceptual event. When a person hears something, that something arrives at the ear as a mechanical sound wave traveling through the air, but within the ear it is transformed into neural action potentials. These nerve pulses then travel to the brain where they are perceived. Hence, in many problems in acoustics, such as for audio 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 ]

The inner ear, for example, does significant signal processing in converting sound waveforms into neural stimuli, this processing renders certain differences between waveforms imperceptible. [2] Data compression techniques, such as MP3, make use of this fact. [3] In addition, the ear has a nonlinear response to sounds of different intensity levels; this nonlinear response is called loudness. Telephone networks and audio noise reduction systems 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, or intermodulation distortion products. [5]

Limits of perception

An equal-loudness contour. Note peak sensitivity around 2-4 kHz, in the middle of the voice frequency band. Perceived Human Hearing.svg
An equal-loudness contour. Note peak sensitivity around 2–4 kHz, in the middle of the voice frequency band.

The human ear can nominally hear sounds in the range 20 to 20000  Hz . The upper limit tends to decrease with age; most adults are unable to hear above 16000 Hz. Under ideal laboratory conditions, the lowest frequency that has been identified as a musical tone is 12 Hz. [6] Tones between 4 and 16 Hz can be perceived via the body's sense of touch.

Human perception of audio signal time separation has been measured to be less than 10 microseconds. This does not mean that frequencies above 100 kHz are 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 of 1000–2000 Hz That 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 as beating.

The semitone scale used in Western musical notation is not a linear frequency scale but logarithmic. Other scales have been derived directly from experiments on human hearing perception, such as the mel scale and Bark 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 few micropascals (μPa) to greater than 100  kPa . For this reason, sound pressure level is also measured logarithmically, with all pressures referenced to 20 μPa (or 1.97385×10−10  atm ). The lower limit of audibility is therefore defined as 0  dB , 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 cause noise-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-dependent absolute threshold of hearing (ATH) curve may be derived. Typically, the ear shows a peak of sensitivity (i.e., its lowest ATH) between 1–5 kHz, though the threshold changes with age, with older ears showing decreased sensitivity above 2 kHz. [9]

The ATH is the lowest of the equal-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 at Bell Labs in 1933 using pure tones reproduced via headphones, and the data they collected are called Fletcher–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 an anechoic chamber. The Robinson-Dadson curves were standardized as ISO 226 in 1986. In 2003, ISO 226 was revised as equal-loudness contour using data collected from 12 international studies.

Sound localization

Sound localization is 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: the azimuth or horizontal angle, the zenith or vertical angle, and the distance (for static sounds) or velocity (for moving sounds). [11] Humans, as most four-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 of owls have their ears placed asymmetrically and can detect sound in all three planes, an adaption to hunt small mammals in the dark. [12]

Masking effects

Audio masking graph Audio Mask Graph.png
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 of backward masking is 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 as MP3.

Missing fundamental

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

Software

Perceptual audio coding uses psychoacoustics-based algorithms. Acustic Block Diagram.svg
Perceptual audio coding uses psychoacoustics-based algorithms.

The psychoacoustic model provides for high quality lossy signal compression by 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 include Dolby Digital (AC-3), MP3, Opus, Ogg Vorbis, AAC, WMA, MPEG-1 Layer II (used for digital audio broadcasting in several countries), and ATRAC, the compression used in MiniDisc and some Walkman models.

Psychoacoustics is based heavily on human 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

Psychoacoustics includes topics and studies that are relevant to music psychology and music therapy. Theorists such as Benjamin Boretz consider some of the results of psychoacoustics to be meaningful only in a musical context. [14]

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

Applied psychoacoustics

Psychoacoustic model Psychoacoustic Model.svg
Psychoacoustic model

Psychoacoustics has long enjoyed a symbiotic relationship with computer science. Internet pioneers J. C. R. Licklider and Bob Taylor both completed graduate-level work in psychoacoustics, while BBN Technologies originally specialized in consulting on acoustics issues before it began building the first packet-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 as MP3 and Opus use a psychoacoustic model to increase compression ratios. The success of conventional audio systems for 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 psychoacoustic sound 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 in sonification to make multiple independent data dimensions audible and easily interpretable. [20] This enables auditory guidance without the need for spatial audio and in sonification computer games [21] and other applications, such as drone flying and image-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 of missing fundamentals to 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

Psychoacoustic topics

Related Research Articles

<span class="mw-page-title-main">Pitch (music)</span> Perceptual property in music ordering sounds from low to high

Pitch is a perceptual property that allows sounds to be ordered on a frequency-related scale, or more commonly, pitch is the quality that makes it possible to judge sounds as "higher" and "lower" in the sense associated with musical melodies. Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre.

<span class="mw-page-title-main">Missing fundamental</span> Acoustic phenomenon

The pitch being perceived with the first harmonic being absent in the waveform is called the missing fundamental phenomenon.

<span class="mw-page-title-main">Absolute threshold of hearing</span> Minimum sound level that an average human can hear

The absolute threshold of hearing (ATH), also known as the absolute hearing threshold or auditory threshold, is the minimum sound level of a pure tone that an average human ear with normal hearing can hear with no other sound present. The absolute threshold relates to the sound that can just be heard by the organism. The absolute threshold is not a discrete point and is therefore classed as the point at which a sound elicits a response a specified percentage of the time.

<span class="mw-page-title-main">Bark scale</span> Auditory frequency metric

The Bark scale is a psychoacoustical scale proposed by Eberhard Zwicker in 1961. It is named after Heinrich Barkhausen, who proposed the first subjective measurements of loudness. One definition of the term is "a frequency scale on which equal distances correspond with perceptually equal distances. Above about 500 Hz this scale is more or less equal to a logarithmic frequency axis. Below 500 Hz the Bark scale becomes more and more linear."

An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch.

<span class="mw-page-title-main">Loudness</span> Subjective perception of sound pressure

In acoustics, loudness is the subjective perception of sound pressure. More formally, it is defined as the "attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics.

<span class="mw-page-title-main">Sonification</span> Use of non-speech audio to convey information

Sonification is the use of non-speech audio to convey information or perceptualize data. Auditory perception has advantages in temporal, spatial, amplitude, and frequency resolution that open possibilities as an alternative or complement to visualization techniques.

<span class="mw-page-title-main">Equal-loudness contour</span> Frequency characteristics of hearing and perceived volume

An equal-loudness contour is a measure of sound pressure level, over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon and is arrived at by reference to equal-loudness contours. By definition, two sine waves of differing frequencies are said to have equal-loudness level measured in phons if they are perceived as equally loud by the average young person without significant hearing impairment.

In audiology and psychoacoustics the concept of critical bands, introduced by Harvey Fletcher in 1933 and refined in 1940, describes the frequency bandwidth of the "auditory filter" created by the cochlea, the sense organ of hearing within the inner ear. Roughly, the critical band is the band of audio frequencies within which a second tone will interfere with the perception of the first tone by auditory masking.

<span class="mw-page-title-main">Hearing range</span> Range of frequencies that can be heard by humans or other animals

Hearing range describes the frequency range that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine investigation for hearing loss usually involves an audiogram which shows threshold levels relative to a normal.

Ultrasonic hearing is a recognised auditory effect which allows humans to perceive sounds of a much higher frequency than would ordinarily be audible using the inner ear, usually by stimulation of the base of the cochlea through bone conduction. Normal human hearing is recognised as having an upper bound of 15–28 kHz, depending on the person.

Perceptual Evaluation of Audio Quality (PEAQ) is a standardized algorithm for objectively measuring perceived audio quality, developed in 1994–1998 by a joint venture of experts within Task Group 6Q of the International Telecommunication Union's Radiocommunication Sector (ITU-R). It was originally released as ITU-R Recommendation BS.1387 in 1998 and last updated in 2023. It utilizes software to simulate perceptual properties of the human ear and then integrates multiple model output variables into a single metric.

Computational auditory scene analysis (CASA) is the study of auditory scene analysis by computational means. In essence, CASA systems are "machine listening" systems that aim to separate mixtures of sound sources in the same way that human listeners do. CASA differs from the field of blind signal separation in that it is based on the mechanisms of the human auditory system, and thus uses no more than two microphone recordings of an acoustic environment. It is related to the cocktail party problem.

In audio signal processing, auditory masking occurs when the perception of one sound is affected by the presence of another sound.

<span class="mw-page-title-main">Sound</span> Vibration that travels via pressure waves in matter

In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.

Tinnitus maskers are a range of devices based on simple white noise machines used to add natural or artificial sound into a tinnitus sufferer's environment in order to mask or cover up the ringing. The noise is supplied by a sound generator, which may reside in or above the ear or be placed on a table or elsewhere in the environment. The noise is usually white noise or music, but in some cases, it may be patterned sound or specially tailored sound based on the characteristics of the person's tinnitus.

<span class="mw-page-title-main">Sub-band coding</span>

In signal processing, sub-band coding (SBC) is any form of transform coding that breaks a signal into a number of different frequency bands, typically by using a fast Fourier transform, and encodes each one independently. This decomposition is often the first step in data compression for audio and video signals.

Ernst Terhardt is a German engineer and psychoacoustician who made significant contributions in diverse areas of audio communication including pitch perception, music cognition, and Fourier transformation. He was professor in the area of acoustic communication at the Institute of Electroacoustics, Technical University of Munich, Germany.

Temporal envelope (ENV) and temporal fine structure (TFS) are changes in the amplitude and frequency of sound perceived by humans over time. These temporal changes are responsible for several aspects of auditory perception, including loudness, pitch and timbre perception and spatial hearing.

Apparent source width (ASW) is the audible impression of a spatially extended sound source. This psychoacoustic impression results from the sound radiation characteristics of the source and the properties of the acoustic space into which it is radiating. Wide source widths are desired by listeners of music because these are associated with the sound of acoustic music, opera, classical music, and historically informed performance. Research concerning ASW comes from the field of room acoustics, architectural acoustics and auralization, as well as musical acoustics, psychoacoustics and systematic musicology.

References

Notes

  1. ↑ Ballou, Glen (2012-11-12). Handbook for Sound Engineers (Fourth ed.). Taylor & Francis. p. 43. ISBN   9781136122538.
  2. ↑ Christopher J. Plack (2005). The Sense of Hearing. Routledge. ISBN   978-0-8058-4884-7.
  3. ↑ Lars Ahlzen; Clarence Song (2003). The Sound Blaster Live! Book. No Starch Press. ISBN   978-1-886411-73-9.
  4. ↑ Rudolf F. Graf (1999). Modern dictionary of electronics. Newnes. ISBN   978-0-7506-9866-5.
  5. ↑ Jack Katz; Robert F. Burkard & Larry Medwetsky (2002). Handbook of Clinical Audiology. Lippincott Williams & Wilkins. ISBN   978-0-683-30765-8.
  6. 1 2 Olson, Harry F. (1967). Music, Physics and Engineering. Dover Publications. pp. 248–251. ISBN   978-0-486-21769-7.
  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.com. Sound On Sound. Archived from the original on 10 March 2023.
  9. ↑ Fastl, Hugo; Zwicker, Eberhard (2006). Psychoacoustics: Facts and Models. Springer. pp. 21–22. ISBN   978-3-540-23159-2.
  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://www.owlpages.com/articles.php?section=Owl+Physiology&title=Hearing [2011, April 5]
  13. ↑ Acoustic, Musical (9 March 2015). "Missing Fundamental". YouTube. Archived from the original on 2021-12-20. Retrieved 19 August 2019.
  14. ↑ Sterne, Jonathan (2003). The Audible Past: Cultural Origins of Sound Reproduction. Durham: Duke University Press. ISBN   9780822330134.
  15. ↑ Cummings, Jim. "Irv Teibel died this week: Creator of 1970s "Environments" LPs". Earth Ear. Retrieved 18 November 2015.
  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. ISBN   978-3-030-23033-3. S2CID   201142606.
  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. ISBN   978-3-030-23032-6. ISSN   2196-6974. S2CID   201136171.
  19. ↑ "Acoustic-Energy Research Hits Sour Note". Archived from the original on 2010-07-19. Retrieved 2010-02-06.
  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. S2CID   125466508.
  21. ↑ CURAT. "Games and Training for Minimally Invasive Surgery". CURAT. University of Bremen. Retrieved 15 July 2020.
  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. Retrieved 10 August 2020.

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