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| {{avnotes}}
| | #redirect [[Sound physics and some human psychoacoustics]] |
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| Psycho-acoustics is a study of various sound response and interpretation effects that happen in the source-ear-brain-perception path, particularly the ear and brain.
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| There are various complex topics in (human) hearing. If you mostly skip this section, the concepts you should probably know about the varying sensitivity to frequencies, know about masking and such, and know that practical psycho-acoustic models (used e.g. for things like sound compression) are mostly a fuzzy combination of various effects.
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| ==Results of said physiology, models==
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| ==Masking==
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| <!--
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| Masking refers to the effect where the presence of one sound influences the perception of another, but often '''simultaneous masking''', referring to simultaneous content masking other parts of it out, primarily by frequency masking, the effect where a frequencies masks out softer content near it. for example, a 1.0kHz tone will make a 1.1kHz tone that is 20dB softer hard to distinguish.
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| * [http://en.wikipedia.org/wiki/Critical_bands Wikipedia: Critical Bands]
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| * [http://en.wikipedia.org/wiki/Bark_scale Wikipedia: Bark scale]
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| * [http://en.wikipedia.org/wiki/Equivalent_rectangular_bandwidth Wikipedia: Equivalent rectangular bandwidth]
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| * http://ccrma.stanford.edu/~jos/sasp/Equivalent_Rectangular_Bandwidth.html
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| * http://home.tm.tue.nl/dhermes/lectures/SoundAndVision/SoundAndVision_notes2.html
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| '''Temporal Masking''' refers to a temporary reduced perception of a tone played immediately before/after another.
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| Forward masking refers to a loud sound triggering reduced sensitivity to a somewhat softer one right after it, for up to perhaps half a second. This is largely based in the ear's ability to protect itself in reaction to loud sounds in the short term (also long, but that is just general reduced hearing).
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| There is also backward masking, where a loud sound ''after'' a softer wound drowns out the perception of the earlier one. The effect works because some of the processing involved is not perceived until perhaps 100ms after reception (frequency and time effects are processed somewhat separately), which is the time window in which this effect works.
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| ==Other time-related effects==
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| More than approximately a dozen short sounds per second are harder to distinguish, which applies to impulses (above that, we start to hear it as a blur, and then a low hum) as well as clear frequencies (very fast piano is hard to distinguish).
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| ==Subjective quality evaluation==
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| In the design of lossy signal processing (e.g. compression), transmission (e.g. phone systems), or
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| * http://en.wikipedia.org/wiki/Sound_Quality
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| * http://en.wikipedia.org/wiki/Audio_quality_measurement
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| ===Algorithms===
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| * PSQM - Perceptual Speech Quality Measure -- '''replaced with:'''
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| * PESQ - Perceptual Evaluation of Speech Quality [http://en.wikipedia.org/wiki/PESQ]
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| * PEAQ (Perceptual Evaluation of Audio Quality) [http://en.wikipedia.org/wiki/PEAQ]
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| http://en.wikipedia.org/wiki/PSQM
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| ===Listening tests===
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| Listening tests are (often double-blind) tests that compare quality by measuring human judgement.
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| * http://en.wikipedia.org/wiki/Codec_listening_test
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| * http://en.wikipedia.org/wiki/Mean_Opinion_Score
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| * http://en.wikipedia.org/wiki/MUSHRA {{comment|(ITU standard)}}
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| * http://en.wikipedia.org/wiki/ABX_test
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| -->
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| ==Other psychoacoustic effects==
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| <!--
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| '''Listener fatigue''' refers to listeners getting used to and tuning out noise content, a partly quantifiable effect.
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| '''Frequency selectivity''' (frequency resolution) is the the effect in which we hear some things as separate sounds and others (such as chords) more as complex but single sounds, which relates to simultaneous masking, but also to harmonic content and other details.
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| '''Localization''' is based on a difference in reception time, which implies a difference in phase.
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| A mild difference in frequency content can be caused by reflective/absorbing nature of obstacles, which can be used for higher-level conclusions such as that the sound is probably coming through a wall, but also for localization as our head and body are also such obstacles.
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| '''Source separation''' refers to the ability to assign frequency content to different sources and selectively focus/ignore on the production of a single source, such as following one conversation among multiple.
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| -->
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| ===Localization===
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| <!--
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| Based on:
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| * relative loudness
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| * timing information
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| * phase information {{verify}}
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| and also:
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| * reflections from the outer ear
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| -->
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| ===Selective attention===
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| {{stub}}
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| <!--
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| See also:
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| * http://en.wikipedia.org/wiki/Selective_attention
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| * http://en.wikipedia.org/wiki/Dichotic_listening
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| -->
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| ===Auditory illusions===
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| <!--
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| The '''Haas effect''' refers to the brain concluding that sounds that would normally be perceived as coming from different origins may be perceived as coming from a single origin, when they arrive within perhaps 40 milliseconds. This seems to be related to a sensory echo cancellation effect that assists localization.
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| Sound engineers may specifically design for this effect when serving large areas, such as for public address systems and concerts.
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| http://en.wikipedia.org/wiki/Haas_effect
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| '''Missing fundamentals''', also known as '''phantom fundamentals''', refer to the effect where overtones suggest a fundamental frequency that the sound actually lacks. Since the brain uses the presence of overtones to make conclusions about the tones it hears, it may fill in the perception of a lower tone that is not physically present.
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| http://en.wikipedia.org/wiki/Missing_fundamental
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| Similarly, '''combination tones''' (also '''sum tones''', '''difference tones''', sometimes '''Tartini tones''') refer to certain simultaneous tones being perceived as having an additional tone {{comment|(where that additional tone's frequencty is the sum, or the difference between the frequencies of the real tones)}}
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| http://en.wikipedia.org/wiki/Combination_tone
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| '''Illusory tone continuity''' refers to the illusion that a tone is continued within a short piece of (spectrum-wide) noise, when that interruption is shorter than about 50ms.
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| http://en.wikipedia.org/wiki/Illusory_continuity_of_tones
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| * http://en.wikipedia.org/wiki/Auditory_illusion
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| * http://en.wikipedia.org/wiki/Combination_tone
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| ==Perceptual filtering==
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| MFC, MFCC
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| -->
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| ==See also==
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| * [http://en.wikipedia.org/wiki/Equal-loudness_contour Wikipedia: Equal loudness contour]
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| * http://www.phys.unsw.edu.au/jw/dB.html (Phons, Sones, dbA, dbC)
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| * http://www2.sfu.ca/sonic-studio/handbook/Phon.html (Phon)
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| * [http://en.wikipedia.org/wiki/A-weighting Wikipedia: A-weighing]
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| * [http://en.wikipedia.org/wiki/ITU-R_468_noise_weighting Wikipedia: ITU-R 468 noise weighting]
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| * http://en.wikipedia.org/wiki/Psychoacoustics
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| * http://en.wikipedia.org/wiki/Music_psychology
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| * Brian Moore, "Introduction to the psychology of hearing"
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| * H. Fastl, E. Zwicker, "Psychoacoustics: Facts and Models" (relatively mathematical)
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| Unsorted:
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| * http://is.rice.edu/~welsh/elec431/psychoAcoustic.html
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| * http://psysound.wikidot.com/
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| * http://www.phys.unsw.edu.au/jw/hearing.html Frequency response self-test (beware of aliasing sound cards, though)
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| [[Category:Audio, video, images]]
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