ISO 31-7 - AbsoluteAstronomy.com

ISO 31-7 is the part of international standard

International standard

International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...

ISO 31

International Standard ISO 31 was the most widely respected style guide for the use of physical quantities and units of measurement, and formulas involving them, in scientific and educational documents worldwide...

that defines names and symbols for quantities

Physical quantity

A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.-Definition of a physical quantity:Formally, the International Vocabulary of Metrology, 3rd edition defines quantity as:...

and units related to acoustics
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

.

Its definitions include:

Quantity			Unit		Remarks
Name	Symbol	Definition	Name	Symbol	Remarks
period Periodic function In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,... , periodic time	T	time of one cycle	second	s
frequency 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...	f, ν	f = 1/T	hertz	Hz	1 Hz = 1 s⁻¹
. . .
loudness level	L_N	L_N = ln(p_eff/p₀)_1 kHz where p_eff is the root-mean-square value of the sound pressure 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... of a pure tone Pure tone A pure tone is a tone with a sinusoidal waveshape.A sine wave is characterized by its frequency, the number of cycles per second—or its wavelength, the distance the waveform travels through its medium within a period—and the amplitude, the size of each cycle... of 1 kHz, which is judged by a normal observer under standardized listening conditions as being as loud as the sound under investigation, and where p₀ = 20 µPa	phon 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.-Definition:The purpose of the phon scale is to compensate for the effect of frequency on the perceived loudness of tones...		The loudness level is 1 phon if 20 log₁₀(p_eff/p₀)_1 kHz=1, that is for a pure tone of frequency 1 kHz, 1 phon = 1 dB sound pressure level. This is not a purely physical quantity and unit, as it involves the subjective evaluation by humans.
loudness Loudness Loudness is the quality of a sound that is primarily a psychological correlate of physical strength . 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."Loudness, a subjective measure, is often...	N	A normal observer's auditory estimate of the ratio between the strength of the sound considered and that of a reference sound having a loudness level of 40 phons	sone 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 intensity...		A standard relation between loudness in sones and loudness level in phons has been adopted for practical use in ISO 131.

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