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Probably the most common usage of "decibels" in reference to sound level is dB SPL, sound pressure level referenced to the nominal threshold of human hearing: [49] The measures of pressure (a root-power quantity) use the factor of 20, and the measures of power (e.g. dB SIL and dB SWL) use the factor of 10.
Standards using different reference levels, give rise to differences in audiograms. The ASA-1951 standard, for example, used a level of 16.5 dB SPL (sound pressure level) at 1 kHz, whereas the later ANSI-1969/ISO-1963 standard uses 6.5 dB SPL, with a 10 dB correction applied for older people.
being approximately the lowest sound intensity hearable by an undamaged human ear under room conditions. The proper notations for sound intensity level using this reference are L I /(1 pW/m 2) or L I (re 1 pW/m 2), but the notations dB SIL, dB(SIL), dBSIL, or dB SIL are very common, even if they are not accepted by the SI. [6]
B-weighted sound pressure level is written either as dB B or L B, and C-weighted sound pressure level is written either as dB C or L C. Unweighted sound pressure level is called "linear sound pressure level" and is often written as dB L or just L. Some sound measuring instruments use the letter "Z" as an indication of linear SPL. [13]
Auditory sensitivity changes when the duration of a sound becomes less than 1 second. The threshold intensity decreases by about 10 dB when the duration of a tone burst is increased from 20 to 200 ms. For example, suppose that the quietest sound a subject can hear is 16 dB SPL if the sound is presented at a duration of 200 ms.
A graph of the A-, B-, C- and D-weightings across the frequency range 10 Hz – 20 kHz Video illustrating A-weighting by analyzing a sine sweep (contains audio). A-weighting is a form of frequency weighting and 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. [1]
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The threshold of hearing is plotted relative to a standardised curve that represents 'normal' hearing, in dB(HL) (hearing level). They are not the same as equal-loudness contours , which are a set of curves representing equal loudness at different levels, as well as at the threshold of hearing , in absolute terms measured in dB(SPL) (sound ...