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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]
Sound exposure level (SEL) is a logarithmic measure of the sound exposure of a sound relative to a reference value. Sound exposure level, denoted L E and measured in dB , is defined by [ 1 ]
Sound has three basic components, the wavelength, frequency, and speed. In sound measurement, we measure the loudness of the sound in decibels (dB). Decibels are logarithmic with 0 dB as the reference. [1] There are also a range of frequencies that sounds can have. Frequency is the number of times a sine wave repeats itself in a second. [2]
Dynamic range is a measure of how small you can measure a signal relative to the maximum input signal the device can measure. Expressed in decibels, the dynamic range is 20 log (Vmax/Vmin). For example, a device with an input range of ±10 V and a dynamic range of 110 dB will be able to measure a signal as small as 10 μV.
The weighting curve is specified by both a circuit diagram of a weighting network and a table of amplitude responses. Above is the ITU-R 468 Weighting Filter Circuit Diagram. The source and sink impedances are both 600 ohms (resistive), as shown in the diagram. The values are taken directly from the ITU-R 468 specification.
Maintenance engineers make them to ensure equipment is still working to specification, or to ensure that the cumulative defects of an audio path are within limits considered acceptable. Audio system measurements often accommodate psychoacoustic principles to measure the system in a way that relates to human hearing.
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]
Loudness, a subjective measure, is often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power. Weighting filters such as A-weighting and LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human.