Loudness
In
In different industries, loudness may have different meanings and different measurement standards. Some definitions, such as
Loudness, a subjective measure, is often confused with physical measures of sound strength such as sound pressure,
Explanation
The perception of loudness is related to
The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud, and different curves pertain to different sound pressure levels. It also shows that humans with normal hearing are most sensitive to sounds around 2–4 kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency.[5]
Historically, loudness was measured using an "ear-balance" audiometer in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. Contemporary standards for measurement of loudness are based on the summation of energy in critical bands.[6]
Hearing loss
When sensorineural hearing loss (damage to the cochlea or in the brain) is present, the perception of loudness is altered. Sounds at low levels (often perceived by those without hearing loss as relatively quiet) are no longer audible to the hearing impaired, but sounds at high levels often are perceived as having the same loudness as they would for an unimpaired listener. This phenomenon can be explained by two theories, called loudness recruitment and softness imperception.
Loudness recruitment posits that loudness grows more rapidly for certain listeners than normal listeners with changes in level. This theory has been accepted as the classical explanation.
Softness imperception, a term coined by Mary Florentine around 2002,[7] proposes that some listeners with sensorineural hearing loss may exhibit a normal rate of loudness growth, but instead have an elevated loudness at their threshold. That is, the softest sound that is audible to these listeners is louder than the softest sound audible to normal listeners.
Compensation
The loudness control associated with a loudness compensation feature on some consumer stereos alters the frequency response curve to correspond roughly with the equal loudness characteristic of the ear.[8] Loudness compensation is intended to make the recorded music sound more natural when played at a lower levels by boosting low frequencies, to which the ear is less sensitive at lower sound pressure levels.
Normalization
Loudness normalization is a specific type of audio normalization that equalizes perceived level such that, for instance, commercials do not sound louder than television programs. Loudness normalization schemes exist for a number of audio applications.
Broadcast
Movie and home theaters
Music playback
- Sound Check in iTunes
- ReplayGain
- Normalization systems built into streaming services such as Spotify and YouTube.
Measurement
Historically sone (loudness N) and phon (loudness level LN) units have been used to measure loudness.[10]
A-weighting follows human sensitivity to sound and describes relative perceived loudness for at quiet to moderate speech levels, around 40 phons.
Relative
The ITU-R BS.1770 measurement system was improved for made multi-channel applications (monaural to 5.1 surround sound). To make the loudness metric cross-genre friendly, a relative measurement gate was added. This work was carried out in 2008 by the EBU. The improvements were brought back into BS.1770-2. ITU subsequently updated the true-peak metric (BS.1770-3) and added provision for even more audio channels, for instance 22.2 surround sound (BS.1770-4).
See also
- Dynamics (music)
- Loudness war
- Sending loudness rating
- Standard siren, loudness measurement in astronomy
Notes
- ^ The relationship between loudness and energy intensity of sound can therefore be approximated by a power function with an exponent of 0.3.
References
- ^ American National Standards Institute, "American national psychoacoustical terminology" S3.20, 1973, American Standards Association.
- S2CID 7190836.
- ISBN 9781412940818.
- ^ Florentine, Mary; Epstein, Michael (2006). "To honor Stevens and repeal his law". Proceedings of the International Society for Psychophysics. 22.
- ^ Olson, Harry (1972). "The Measurement of Loudness". Audio Magazine.
- ^ As described in IEC 532, DIN 45631 and ASA/ANSI S3.4
- .
- ISBN 0-07-038185-2.
- ^ EBU Recommendation R 128: Loudness normalisation and permitted maximum level of audio signals (PDF). European Broadcasting Union. August 2011. Retrieved 2013-04-22.
- ^ Olson, Harry F. (February 1972). "The Measurement of Loudness" (PDF). Audio: 18–22.
- ^ Recommendation BS.1770. International Telecommunication Union. August 2012. Retrieved 2013-05-31.
- ^ "Leq Meter". Retrieved 2015-12-15.
External links
- Media related to Loudness at Wikimedia Commons