ISO 31-7

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 It is superseded by ISO 80000-8.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:

Quantity Unit Remarks
periodic time
Ttime of one cycleseconds
frequencyf, νf = 1/ThertzHz1 Hz = 1 s−1
loudness levelLNLN = 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 µPaphon 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.
loudnessNA 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 phonssone 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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