ISO 31-7

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ISO 31-7 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to acoustics . It is superseded by ISO 80000-8.

Its definitions include:

QuantityUnitRemarks
NameSymbolDefinitionNameSymbol
period,
periodic time
Ttime of one cycleseconds
frequency f, νf = 1/ThertzHz1 Hz = 1 s−1
.
.
.
loudness level LNLN = ln(peff/p0)1 kHz where peff is the root-mean-square value of the sound pressure of a pure tone 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 The loudness level is 1 phon if 20 log10(peff/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 NA 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 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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