423:. Even today, the best speakers are likely to generate around 1 to 3% of total harmonic distortion, corresponding to 30 to 40 dB below fundamental. This is not good enough, given the steep rise in loudness (rising to as much as 24 dB per octave) with frequency revealed by the equal-loudness curves below about 100 Hz. A good experimenter must ensure that trial subjects really hear the fundamental and not harmonics—especially the third harmonic, which is especially strong as a speaker cone's travel becomes limited as its suspension reaches the limit of compliance. A possible way around the problem is to use acoustic filtering, such as by resonant cavity, in the speaker setup. A flat free-field high-frequency response up to 20 kHz, on the other hand, is comparatively easy to achieve with modern speakers on-axis. These effects must be considered when comparing results of various attempts to measure equal-loudness contours.
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resonances. Headphone testing is, therefore, a good way to derive equal-loudness contours below about 500 Hz, though reservations have been expressed about the validity of headphone measurements when determining the actual threshold of hearing, based on the observation that closing off the ear canal produces increased sensitivity to the sound of blood flow within the ear, which the brain appears to mask in normal listening conditions. At high frequencies, headphone measurement becomes unreliable, and the various resonances of pinnae (outer ears) and ear canals are severely affected by proximity to the headphone cavity.
155:(1933). In their study, test subjects listened to pure tones at various frequencies and over 10 dB increments in stimulus intensity. For each frequency and intensity, the listener also listened to a reference tone at 1000 Hz. Fletcher and Munson adjusted the reference tone until the listener perceived that it had the same loudness as the test tone. Loudness, being a psychological quantity, is difficult to measure, so Fletcher and Munson averaged their results over many test subjects to derive reasonable averages. The lowest equal-loudness contour represents the quietest audible tone—the
443:. The high-frequency bands are wider in absolute terms than the low-frequency bands, and therefore "collect" proportionately more power from a noise source. However, when more than one critical band is stimulated, the signals to the brain add the various bands to produce the impressions of loudness. For these reasons equal-loudness curves derived using noise bands show an upwards tilt above 1 kHz and a downward tilt below 1 kHz when compared to the curves derived using pure tones.
22:
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86:, that boosts low and high-frequency components of the sound. These are intended to offset the apparent loudness fall-off at those frequencies, especially at lower volume levels. Boosting these frequencies produces a flatter equal-loudness contour that appears to be louder even at low volume, preventing the perceived sound from being dominated by the mid-frequencies where the ear is most sensitive.
190:(ISO) to revise the standard curves in ISO 226. They did this in response to recommendations in a study coordinated by the Research Institute of Electrical Communication, Tohoku University, Japan. The study produced new curves by combining the results of several studies—by researchers in Japan, Germany, Denmark, UK, and the US. (Japan was the greatest contributor with about 40% of the data.)
95:
439:—is said to have been based on the 40-phon Fletcher–Munson curve. However, research in the 1960s demonstrated that determinations of equal-loudness made using pure tones are not directly relevant to our perception of noise. This is because the cochlea in our inner ear analyzes sounds in terms of spectral content, each "hair-cell" responding to a narrow band of frequencies known as a
193:
This has resulted in the recent acceptance of a new set of curves standardized as ISO 226:2003. The report comments on the surprisingly large differences, and the fact that the original
Fletcher–Munson contours are in better agreement with recent results than the Robinson–Dadson, which appear to
472:
conducted listening trials in an attempt to find the best weighting curve and rectifier combination for use when measuring noise in broadcast equipment, examining the various new weighting curves in the context of noise rather than tones, confirming that they were much more valid than A-weighting
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Good headphones, well sealed to the ear, provide a flat low-frequency pressure response to the ear canal, with low distortion even at high intensities. At low frequencies, the ear is purely pressure-sensitive, and the cavity formed between headphones and ear is too small to introduce modifying
513:
to account for our reduced sensitivity to short bursts and clicks. It is widely used by
Broadcasters and audio professionals when they measure noise on broadcast paths and audio equipment, so they can subjectively compare equipment types with different noise spectra and characteristics.
302:
Real-life sounds from a reasonably distant source arrive as planar wavefronts. If the source of sound is directly in front of the listener, then both ears receive equal intensity, but at frequencies above about 1 kHz the sound that enters the ear canal is partially reduced by the
311:(outer ear). Off-centre sounds result in increased head masking at one ear, and subtle changes in the effect of the pinna, especially at the other ear. This combined effect of head-masking and pinna reflection is quantified in a set of curves in three-dimensional space referred to as
52:
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.
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produced a new experimental determination that they believed was more accurate. It became the basis for a standard (ISO 226) that was considered definitive until 2003, when ISO revised the standard on the basis of recent assessments by research groups worldwide.
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and a variety of other sounds that, because of their brief impulsive nature, do not give the ear and brain sufficient time to respond. The results were reported in BBC Research Report EL-17 1968/8 entitled
197:
According to the ISO report, the
Robinson–Dadson results were the odd one out, differing more from the current standard than did the Fletcher–Munson curves. The report states that it is fortunate that the
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458:, which differed from the A-weighting curve, showing more of a peak around 6 kHz. These gave a more meaningful subjective measure of noise on audio equipment, especially on the newly invented
329:, and for a long time the difference from the Fletcher–Munson curves was explained partly on the basis that the latter used headphones. However, the ISO report actually lists the latter as using
315:(HRTFs). Frontal presentation is now regarded as preferable when deriving equal-loudness contours, and the latest ISO standard is specifically based on frontal and central presentation.
101:
The first research on the topic of how the ear hears different frequencies at different levels was conducted by
Fletcher and Munson in 1933. Until recently, it was common to see the term
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used to refer to equal-loudness contours generally, even though a re-determination was carried out by
Robinson and Dadson in 1956, which became the basis for an ISO 226 standard.
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Churcher and King carried out a second determination in 1937, but their results and
Fletcher and Munson's showed considerable discrepancies over parts of the auditory diagram.
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that is free from reflections down to 20 Hz. Until recently, it was not possible to achieve high levels at frequencies down to 20 Hz without high levels of
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Because no HRTF is involved in normal headphone listening, equal-loudness curves derived using headphones are valid only for the special case of what is called
112:
is now preferred, of which the
Fletcher–Munson curves are now a sub-set, and especially since a 2003 survey by ISO redefined the curves in a new standard.
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With speakers, the opposite is true. A flat low-frequency response is hard to obtain—except in free space high above ground, or in a very large and
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when attempting to measure the subjective loudness of noise. This work also investigated the response of human hearing to tone-bursts, clicks,
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The report also comments on the large differences apparent in the low-frequency region, which remain unexplained. Possible explanations are:
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Subjects were not properly rested for days in advance, or were exposed to loud noise in traveling to the tests, which tensed the
68:. Fletcher–Munson curves have been superseded and incorporated into newer standards. The definitive curves are those defined in
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and Wilden A. Munson, and reported in a 1933 paper entitled "Loudness, its definition, measurement and calculation" in the
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to a maximum of around 20,000 Hz, although the upper hearing limit decreases with age. Within this range, the
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differ by as much as 10–15 dB, especially in the low-frequency region, for reasons not explained.
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noise reduction, which were characterized by a noise spectrum dominated by the higher frequencies.
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are one of many sets of equal-loudness contours for the human ear, determined experimentally by
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when presented with pure steady tones. The unit of measurement for loudness levels is the
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Fletcher, H. and Munson, W. A. "Loudness, its definition, measurement and calculation",
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Full
Revision of International Standards for Equal-Loudness Level Contours (ISO 226)
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The criteria used for judging equal loudness at different frequencies had differed.
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standard was based turns out to have been in agreement with modern determinations.
76:, which are based on a review of modern determinations made in various countries.
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762:"Precise and Full-range Determination of Two-dimensional Equal Loudness Contours"
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Precise and Full-range
Determination of Two-dimensional Equal Loudness Contours
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Perceived discrepancies between early and more recent determinations led the
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headphones, though it doesn't make clear how
Robinson–Dadson achieved
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Test your hearing – A tool for measuring your equal-loudness contours
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685:"Fletcher Munson Curve: The Equal Loudness Contour of Human Hearing"
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recommendation 468, but later adopted by numerous standards bodies (
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742:"A re-determination of the equal-loudness relations for pure tones"
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A Model of Loudness Applicable to Time-Varying Sounds AESJ Article
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Recent revision aimed at more precise determination – ISO 226:2023
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Fletcher and Munson first measured equal-loudness contours using
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800:"A measurement of equal-loudness level contours for tone burst"
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auditory system is sensitive to frequencies from about 20
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823:, 2nd Ed., 1999, edited Michael Talbot Smith, Focal Press.
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Frequency characteristics of hearing and perceived volume
509:) was based on the research, and incorporates a special
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were derived in the 1960s, in particular as part of the
340:
82:
often feature a "loudness" button, known technically as
125:
871:
Evaluation of Loudness-level weightings and LLSEL JASA
910:
798:
Ken’ichiro Masaoka, Kazuho Ono, and Setsu Komiyama,
44:
spectrum, for which a listener perceives a constant
480:
The Assessment of Noise in Audio Frequency Circuits
231:
307:, and also highly dependent on reflection off the
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612:The Journal of the Acoustical Society of America
787:IEEE Transactions on Audio and Electroacoustics
605:
427:Relevance to sound level and noise measurements
213:The equipment used was not properly calibrated.
608:"Equal-loudness-level contours for pure tones"
227:controlling low-frequency mechanical coupling.
188:International Organization for Standardization
74:International Organization for Standardization
3225:
896:
866:Equal-loudness contour measurements in detail
115:
851:Fletcher–Munson is not Robinson–Dadson (PDF)
827:An Introduction to the Psychology of Hearing
672:Journal of the Acoustical Society of America
66:Journal of the Acoustical Society of America
28:equal-loudness contours with frequency in Hz
379:. Unsourced material may be challenged and
270:. Unsourced material may be challenged and
3232:
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903:
889:
606:Suzuki, YĂ´iti; Takeshima, Hisashi (2004).
829:5th ed, Brian C.J. Moore, Elsevier Press.
710:
708:
706:
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399:Learn how and when to remove this message
290:Learn how and when to remove this message
89:
20:
325:The Robinson–Dadson determination used
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703:
322:, which is not how we normally hear.
136:, largely due to the resonance of the
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341:Headphones versus loudspeaker testing
783:"Researches in loudness measurement"
377:adding citations to reliable sources
344:
268:adding citations to reliable sources
235:
789:, Vol. 14:3 (Sep 1966), pp.141–151.
202:Fletcher–Munson curve on which the
13:
132:is most sensitive between 2 and 5
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14:
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806:, Vol. 22 (2001), No. 1 pp.35–39.
804:Acoustical Science and Technology
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232:Side versus frontal presentation
821:Audio Engineer's Reference Book
313:head-related transfer functions
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540:CCIR (ITU) 468 Noise Weighting
489:curve, originally proposed in
1:
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161:. The highest contour is the
158:absolute threshold of hearing
562:, the same concept in vision
435:curve—in widespread use for
7:
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10:
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116:Experimental determination
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1991:
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751:(1956), pp. 166–181.
550:ITU-R 468 noise weighting
530:Audio quality measurement
487:ITU-R 468 noise weighting
456:audio quality measurement
592:
3257:Architectural acoustics
781:Bauer, B., Torick, E.,
740:D. W. Robinson et al.,
110:equal-loudness contours
3344:Fletcher–Munson curves
3339:Equal-loudness contour
3249:Acoustical engineering
760:YĂ´iti Suzuki, et al.,
576:Robinson–Dadson curves
98:
90:Fletcher–Munson curves
58:Fletcher–Munson curves
34:equal-loudness contour
29:
3480:Hermann von Helmholtz
3378:Fundamental frequency
3282:Sympathetic resonance
730:on September 27, 2007
97:
84:loudness compensation
24:
571:Pure tone audiometry
462:tape recorders with
373:improve this section
264:improve this section
38:sound pressure level
3500:Werner Meyer-Eppler
3410:Missing fundamental
624:2004ASAJ..116..918S
560:Luminosity function
511:quasi-peak detector
421:harmonic distortion
175:Robinson and Dadson
148:of the middle ear.
3383:Frequency spectrum
916:by standard number
768:2007-09-27 at the
746:Br. J. Appl. Phys.
691:. 16 November 2017
454:4550 standard for
99:
30:
3612:Audio engineering
3594:
3593:
3556:Musical acoustics
3388:harmonic spectrum
3207:
3206:
930:ISO romanizations
674:5, 82–108 (1933).
633:10.1121/1.1763601
581:Sound level meter
437:noise measurement
409:
408:
401:
320:side-presentation
300:
299:
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225:stapedius muscles
164:threshold of pain
142:transfer function
108:The generic term
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3583:
3485:Carleen Hutchins
3417:Combination tone
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3277:String vibration
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723:, archived from
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586:Weighting filter
555:Listener fatigue
460:compact cassette
448:weighting curves
417:anechoic chamber
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36:is a measure of
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3607:Psychoacoustics
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3515:D. Van Holliday
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3422:Mersenne's laws
3356:Audio frequency
3350:
3314:Psychoacoustics
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770:Wayback Machine
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103:Fletcher–Munson
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62:Harvey Fletcher
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3529:Related topics
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3495:Marin Mersenne
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3290:
3289:
3287:
3285:
3284:
3279:
3274:
3269:
3264:
3259:
3253:
3251:
3245:
3244:
3237:
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3229:
3222:
3214:
3205:
3204:
3202:
3201:
3190:
3187:
3186:
3184:
3183:
3178:
3173:
3168:
3163:
3158:
3153:
3148:
3143:
3138:
3133:
3128:
3123:
3117:
3115:
3111:
3110:
3108:
3107:
3102:
3097:
3092:
3089:
3084:
3079:
3074:
3069:
3064:
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3019:
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2999:
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2979:
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2701:
2696:
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2676:
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2646:
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2636:
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2621:
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2601:
2596:
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2238:
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2228:
2223:
2218:
2213:
2208:
2198:
2193:
2188:
2183:
2178:
2173:
2168:
2163:
2158:
2153:
2148:
2143:
2138:
2133:
2128:
2123:
2118:
2113:
2108:
2103:
2098:
2093:
2088:
2083:
2082:
2081:
2076:
2071:
2066:
2061:
2051:
2046:
2041:
2036:
2031:
2026:
2021:
2016:
2011:
2006:
2001:
1995:
1993:
1989:
1988:
1986:
1985:
1980:
1975:
1970:
1965:
1960:
1955:
1950:
1945:
1940:
1935:
1930:
1925:
1920:
1915:
1910:
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1900:
1895:
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1596:
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1471:
1466:
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1456:
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1394:
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1379:
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1199:
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985:
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965:
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944:
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923:
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835:External links
833:
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733:
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618:(2): 918–933.
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221:tensor tympani
217:
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114:
91:
88:
15:
9:
6:
4:
3:
2:
3639:
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3617:ISO standards
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3505:Lord Rayleigh
3503:
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3498:
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3478:
3476:
3475:Ernst Chladni
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3456:
3450:
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3437:Standing wave
3435:
3433:
3430:
3428:
3425:
3423:
3420:
3418:
3415:
3411:
3408:
3406:
3405:Inharmonicity
3403:
3401:
3398:
3397:
3396:
3393:
3389:
3386:
3385:
3384:
3381:
3379:
3376:
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3357:
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3333:
3330:
3328:
3325:
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3320:
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3317:
3315:
3311:
3303:
3299:
3296:
3292:
3291:
3283:
3280:
3278:
3275:
3273:
3272:Soundproofing
3270:
3268:
3267:Reverberation
3265:
3263:
3260:
3258:
3255:
3254:
3252:
3250:
3246:
3242:
3235:
3230:
3228:
3223:
3221:
3216:
3215:
3212:
3200:
3192:
3191:
3188:
3182:
3179:
3177:
3174:
3172:
3169:
3167:
3164:
3162:
3159:
3157:
3154:
3152:
3149:
3147:
3144:
3142:
3139:
3137:
3134:
3132:
3129:
3127:
3124:
3122:
3119:
3118:
3116:
3112:
3106:
3103:
3101:
3098:
3096:
3093:
3090:
3088:
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3083:
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3023:
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3018:
3015:
3013:
3010:
3008:
3005:
3003:
3000:
2998:
2995:
2993:
2990:
2988:
2985:
2983:
2980:
2978:
2975:
2973:
2970:
2968:
2965:
2963:
2960:
2958:
2955:
2953:
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2948:
2945:
2943:
2940:
2938:
2935:
2933:
2930:
2928:
2925:
2923:
2920:
2918:
2915:
2913:
2910:
2908:
2905:
2903:
2900:
2898:
2895:
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2890:
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2885:
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2807:
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2802:
2799:
2797:
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2779:
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2700:
2697:
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2670:
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2662:
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2657:
2655:
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2647:
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2642:
2640:
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2174:
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2167:
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2159:
2157:
2154:
2152:
2149:
2147:
2144:
2142:
2139:
2137:
2134:
2132:
2129:
2127:
2124:
2122:
2119:
2117:
2114:
2112:
2109:
2107:
2104:
2102:
2099:
2097:
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2089:
2087:
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2032:
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2027:
2025:
2022:
2020:
2017:
2015:
2012:
2010:
2007:
2005:
2002:
2000:
1997:
1996:
1994:
1990:
1984:
1981:
1979:
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1971:
1969:
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1944:
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1517:
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1510:
1507:
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1500:
1497:
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1490:
1487:
1485:
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1477:
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1467:
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1325:
1323:
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1305:
1303:
1300:
1298:
1295:
1293:
1290:
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1283:
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1275:
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1268:
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1225:
1223:
1220:
1218:
1215:
1213:
1210:
1208:
1205:
1203:
1200:
1198:
1195:
1193:
1190:
1188:
1185:
1183:
1180:
1178:
1175:
1171:
1168:
1166:
1163:
1161:
1158:
1156:
1153:
1151:
1148:
1147:
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1143:
1141:
1138:
1136:
1133:
1131:
1128:
1126:
1123:
1121:
1118:
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1111:
1108:
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1101:
1098:
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1024:
1021:
1019:
1016:
1014:
1011:
1009:
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996:
995:
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989:
986:
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976:
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966:
964:
961:
959:
956:
954:
951:
949:
946:
945:
943:
939:
935:
934:IEC standards
931:
927:
926:ISO standards
921:
913:
906:
901:
899:
894:
892:
887:
886:
883:
877:
874:
872:
869:
867:
864:
862:
859:
857:
854:
852:
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441:critical band
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358:This section
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280:December 2020
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249:This section
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35:
27:
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19:
3520:Thomas Young
3470:Jens Blauert
3458:Acousticians
3338:
3052:27000 series
1084:
841:ISO Standard
826:
820:
803:
794:
786:
777:
756:
748:
745:
736:
725:the original
717:ISO 226:2003
716:
695:November 17,
693:. Retrieved
688:
679:
671:
666:
615:
611:
601:
484:
479:
470:BBC Research
468:
445:
430:
414:
410:
395:
389:October 2015
386:
371:Please help
359:
335:compensation
334:
330:
327:loudspeakers
324:
319:
317:
301:
286:
277:
262:Please help
250:
208:
196:
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185:
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156:
150:
119:
109:
107:
102:
100:
78:
69:
65:
57:
55:
33:
31:
18:
3490:Franz Melde
3465:John Backus
3449:Subharmonic
3302:Spectrogram
2840:20000–29999
1992:10000–19999
689:Ledger Note
525:A-weighting
433:A-weighting
331:compensated
305:head shadow
204:A-weighting
40:, over the
3601:Categories
3551:Ultrasound
3541:Infrasound
3327:Bark scale
2619:16949 (TS)
2216:11941 (TR)
914:standards
814:References
475:pink noise
153:headphones
80:Amplifiers
3627:Acoustics
3432:Resonance
3332:Mel scale
3262:Monochord
3241:Acoustics
2574:15926 WIP
1938:9592/9593
1863:9000/9001
1751:8805/8806
642:0001-4966
566:Mel scale
535:Audiogram
360:does not
251:does not
138:ear canal
130:human ear
72:from the
42:frequency
3586:Category
3427:Overtone
3395:Harmonic
3199:Category
924:List of
766:Archived
658:15865914
650:15376658
518:See also
446:Various
173:In 1956
146:ossicles
140:and the
46:loudness
3373:Formant
3100:29199-2
2972:23094-2
2967:23094-1
2957:23090-3
2826:19794-5
2821:19775-1
2609:16612-2
2599:16355-1
2288:13406-2
2246:12234-2
2014:10118-3
620:Bibcode
381:removed
366:sources
272:removed
257:sources
144:of the
70:ISO 226
3566:Violin
3400:Series
3114:30000+
1953:9797-1
1761:8820-5
1706:8501-1
1262:1073-2
1257:1073-1
941:1–9999
656:
648:
640:
3622:Sound
3561:Piano
3546:Sound
3360:pitch
3322:Pitch
3181:80000
3176:56000
3171:55000
3166:50001
3161:45001
3156:42010
3151:40500
3146:39075
3141:38500
3136:37001
3131:32000
3126:31000
3121:30170
3105:29500
3095:29148
3091:29110
3087:28000
3082:27729
3077:27006
3072:27005
3067:27002
3062:27001
3057:27000
3047:26324
3042:26300
3037:26262
3032:26000
3027:25964
3022:25178
3017:24728
3012:24707
3007:24617
3002:24613
2997:24517
2992:23941
2987:23360
2982:23271
2977:23270
2962:23092
2952:23009
2947:23008
2942:23003
2937:23000
2932:22537
2927:22395
2922:22301
2917:22300
2912:22275
2907:22000
2902:21827
2897:21500
2892:21122
2887:21047
2882:21001
2877:21000
2872:20830
2867:20802
2862:20400
2857:20121
2852:20022
2847:20000
2831:19831
2816:19770
2811:19757
2806:19752
2801:19600
2796:19510
2791:19509
2786:19508
2781:19507
2776:19506
2771:19505
2766:19503
2761:19502
2756:19501
2751:19500
2746:19439
2741:19407
2736:19136
2731:19125
2726:19115
2721:19114
2704:19092
2699:19011
2694:19005
2689:18916
2684:18629
2679:18245
2674:18181
2669:18014
2664:18004
2659:17799
2654:17506
2649:17442
2644:17369
2639:17203
2634:17100
2629:17025
2624:17024
2614:16750
2604:16485
2594:16262
2589:16023
2584:15938
2579:15930
2569:15926
2564:15924
2559:15919
2554:15897
2549:15707
2537:15706
2532:15693
2527:15686
2522:15511
2517:15504
2512:15438
2507:15445
2490:15444
2485:15408
2480:15398
2475:15291
2470:15288
2465:15189
2460:15022
2455:14971
2450:14882
2445:14764
2440:14698
2435:14651
2430:14649
2425:14644
2420:14617
2368:14496
2363:14443
2358:14396
2353:14289
2348:14224
2343:14031
2338:14000
2333:13818
2328:13816
2323:13616
2318:13584
2313:13568
2308:13567
2303:13490
2298:13485
2293:13450
2283:13399
2278:13250
2273:13216
2256:13211
2251:12620
2241:12207
2236:12182
2231:12052
2226:12006
2221:11992
2211:11941
2201:11940
2196:11898
2191:11889
2186:11801
2181:11785
2176:11784
2171:11783
2166:11544
2161:11404
2156:11179
2151:11172
2146:11170
2141:11073
2136:10967
2131:10962
2126:10957
2121:10861
2116:10746
2111:10664
2106:10646
2101:10628
2096:10589
2091:10585
2086:10383
2054:10303
2049:10279
2044:10218
2039:10206
2034:10179
2029:10165
2024:10161
2019:10160
2009:10116
2004:10007
1999:10006
728:(PDF)
721:(PDF)
654:S2CID
593:Notes
545:dB(A)
464:Dolby
309:pinna
122:human
3536:Echo
3442:Node
3368:Beat
3358:and
2079:-238
1983:9995
1978:9985
1973:9984
1968:9945
1963:9899
1958:9897
1948:9660
1943:9594
1933:9564
1928:9529
1923:9506
1918:9496
1913:9407
1908:9362
1903:9314
1898:9293
1893:9241
1888:9227
1883:9141
1878:9126
1873:9075
1868:9036
1858:8879
1811:-8-I
1766:8859
1756:8807
1746:8691
1741:8652
1736:8651
1731:8632
1726:8613
1721:8601
1716:8583
1711:8571
1701:8373
1696:8217
1691:8178
1686:8093
1681:8000
1676:7942
1671:7816
1666:7813
1661:7812
1656:7811
1651:7810
1646:7736
1641:7637
1629:7498
1624:7200
1619:7185
1614:7098
1609:7064
1604:7027
1599:7010
1594:7002
1589:7001
1584:6943
1579:6709
1574:6523
1569:6438
1564:6429
1559:6425
1554:6385
1549:6373
1544:6346
1539:6344
1534:6166
1529:5964
1524:5807
1519:5800
1514:5776
1509:5775
1504:5725
1499:5428
1494:5427
1489:5426
1484:5218
1479:4909
1474:4217
1469:4165
1464:4157
1459:4031
1454:3977
1449:3950
1444:3901
1439:3864
1434:3602
1429:3601
1424:3307
1419:3297
1397:3166
1392:3103
1387:3029
1382:2921
1377:2852
1372:2848
1367:2788
1362:2720
1357:2711
1352:2709
1347:2533
1342:2281
1337:2240
1332:2146
1327:2145
1322:2108
1317:2047
1312:2033
1307:2022
1302:2015
1297:2014
1292:1989
1287:1745
1282:1629
1277:1538
1272:1413
1267:1155
1252:1007
1247:1004
1242:1000
1065:68-1
697:2017
646:PMID
638:ISSN
491:CCIR
485:The
431:The
364:any
362:cite
255:any
253:cite
223:and
200:phon
120:The
56:The
50:phon
2413:-20
2408:-17
2403:-14
2398:-12
2393:-11
2388:-10
2074:-28
2069:-22
2064:-21
2059:-11
1851:-16
1846:-15
1841:-14
1836:-13
1831:-12
1826:-11
1821:-10
1237:999
1232:965
1227:898
1222:860
1217:843
1212:838
1207:764
1202:732
1197:704
1192:690
1187:668
1182:657
1177:646
1145:639
1140:519
1135:518
1130:500
1125:361
1120:306
1115:302
1110:262
1105:261
1100:259
1095:233
1090:228
1085:226
1080:217
1075:216
1070:128
1058:-13
1053:-12
1048:-11
1043:-10
912:ISO
628:doi
616:116
507:ITU
503:JIS
499:BSI
495:IEC
452:DIN
375:by
266:by
198:40-
134:kHz
32:An
26:ISO
3603::
2714:-2
2709:-1
2542:-2
2500:-9
2495:-3
2383:-6
2378:-3
2373:-2
2266:-2
2261:-1
2205:-2
1816:-9
1806:-8
1801:-7
1796:-6
1791:-5
1786:-4
1781:-3
1776:-2
1771:-1
1634:-1
1412:-3
1407:-2
1402:-1
1170:-6
1165:-5
1160:-3
1155:-2
1150:-1
1038:-9
1033:-8
1028:-7
1023:-6
1018:-5
1013:-4
1008:-3
1003:-1
998:-0
993:31
988:17
983:16
932:–
928:–
802:,
785:,
764:.
744:,
705:^
687:.
652:.
644:.
636:.
626:.
614:.
610:.
505:,
501:,
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126:Hz
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630::
622::
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387:(
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369:.
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287:(
282:)
278:(
274:.
260:.
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