Loudness is the quality of a sound Sound is a travelling wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations that is the primary psychological correlate of physical strength (amplitude Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system). More formally, it is defined as "that attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud."[1]
The horizontal axis shows frequency Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency. Loosely speaking, 1 year is the period of the Earth's orbit around the Sun, and the Earth's rotation on its axis has in Hz The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sine wave, particularly those used in radio and audio applicationsLoudness, a subjective measure, is often confused with objective measures of sound strength such as sound pressure Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The SI unit for sound pressure p is the pascal (symbol: Pa), sound pressure level (in decibels The decibel is a logarithmic unit for the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities. Being a ratio of two measurements of a physical quantity in the same units, it is a dimensionless), sound intensity The sound intensity, I, is defined as the sound power Pac per unit area A. The usual context is the noise measurement of sound intensity in the air at a listener's location. For instantaneous acoustic pressure pinst(t) and particle velocity v(t) the average acoustic intensity during time T is given by or sound power Sound power or acoustic power Pac is a measure of sonic energy E per time t unit. Filters such as A-weighting A-weighting is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level .[dubious – discuss] The others are B, C, D and now Z weightings (see below) attempt to adjust sound measurements to correspond to loudness as perceived by the typical human. However, loudness perception is a much more complex process than A-weighting. Furthermore, as the perception of loudness varies from person to person it cannot be universally measured using any single metric.
Loudness is also affected by parameters other than sound pressure, including frequency, bandwidth and duration. In acoustics volume is related to amplitude, sound pressure, and dynamics.
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Explanation
The perception of loudness is related to both the sound pressure level and duration of a sound. The human auditory system integrates (averages) the effects of sound pressure level (SPL) over a 600–1,000 ms window. For example, a sound of constant SPL will be perceived to increase in loudness as 20, 50, 100, 200 ms samples are played, up to a maximum of approximately 1 second at which point the perception of loudness will stabilize. For long duration sounds (greater than 1 second), the moment by moment perception of loudness will be based on the integration of the preceding 600–1,000 ms.
In terms of the relationship between SPL and loudness for sounds longer than 1 second, this can be approximated by a power function with an exponent of 0.6 when plotted against sound pressure or 0.3 when plotted against sound intensity (Stevens' power law). More precise measures have been subsequently made that show that loudness grows more rapidly (with a higher exponent) at low and high levels and less rapidly (with a lower exponent) at moderate levels.
Units used to measure loudness:
- Sone The sone was proposed as a unit of perceived loudness by Stanley Smith Stevens in 1936. In acoustics, loudness is the subjective perception of sound pressure. Although defined by Stevens as a unit, it is not one of the SI units. Such units meet the stringent criteria of metrology, which include being realizable in a highly precise and reproducible (loudness N)
- Phon The phon was proposed in DIN 45631 and ISO 532 B as a unit of perceived loudness level LN for pure tones by S. S. Stevens (loudness level L)
The sensitivity of the human ear changes as a function of frequency, as shown on the graph to the right. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud. It also shows that humans with good 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 and the duration of each.
Loudness and hearing loss
When sensorineural hearing loss (damage to the cochlea The cochlea is the auditory portion of the inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of 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 interestingly, 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: Loudness grows more rapidly for these listeners than normal listeners with changes in level. This theory is called "loudness recruitment" and has been accepted as the classical explanation. More recently, it has been proposed that some listeners with sensorineural hearing loss may in fact 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. This theory is called "softness imperception."[citation needed]
Other uses of the word loudness
The "loudness" control on some consumer stereos may alter the frequency response Frequency response is the measure of any system's output spectrum in response to an input signal. In the audible range it is usually referred to in connection with electronic amplifiers, microphones and loudspeakers. Radio spectrum frequency response can refer to measurements of coaxial cables, category cables, video switchers and wireless curve to correspond roughly with the equal loudness characteristic of the ear.[2] The loudness control is intended to make the recorded music sound more natural when played at a lower sound pressure level.
See also
- Loudness war
- Loudness compensation
- Sending loudness rating
- Volume in acoustics is related to:
- Amplitude Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system
- Sound pressure Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The SI unit for sound pressure p is the pascal (symbol: Pa)
- Dynamics In music, dynamics normally refers to the volume of a sound or note, but can also refer to every aspect of the execution of a given piece, either stylistic or functional (velocity). The term is also applied to the written or printed musical notation used to indicate dynamics. Dynamics do not indicate specific volume levels, but are meant to be
References
- ^ American National Standards Institute, "American national psychoacoustical terminology" S3.20, 1973, American Standards Association.
- ^ Lenk, John D. (1998). Circuit Troubleshooting Handbook. McGraw-Hill The McGraw-Hill Companies, Inc., is a publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are education, publishing, broadcasting, and financial and business services. It publishes numerous textbooks and magazines, including Architectural Record and Aviation Week, and is the parent. p. 163. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0070381852.
Categories: Aspects of music | Acoustics Acoustics is a branch of physics and is study of sound, mechanical waves in gases, liquids, and solids
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