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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]
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]
The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. Until the mid-1920s, the unit for loss was miles of standard cable (MSC). 1 MSC corresponded to the loss of power over one mile (approximately 1.6 km) of standard telephone cable at a frequency of 5000 radians per second (795.8 Hz), and matched closely the smallest attenuation detectable to a ...
I 0 is the reference sound intensity; 1 Np = 1 is the neper; 1 B = 1 / 2 ln(10) is the bel; 1 dB = 1 / 20 ln(10) is the decibel. The commonly used reference sound intensity in air is [5] = /. being approximately the lowest sound intensity hearable by an undamaged human ear under room conditions.
A noise dosimeter (American) or noise dosemeter (British) is a specialized sound level meter intended specifically to measure the noise exposure of a person integrated over a period of time; usually to comply with Health and Safety regulations such as the Occupational Safety and Health (OSHA) 29 CFR 1910.95 Occupational Noise Exposure Standard ...
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 ]
Signal-to-noise ratio (SNR), however, is the ratio between the noise floor and an arbitrary reference level or alignment level. In "professional" recording equipment, this reference level is usually +4 dBu (IEC 60268-17), though sometimes 0 dBu (UK and Europe – EBU standard Alignment level).
Multiple noise processes determine the noise floor of a system. Noise can be picked up from microphone self-noise, preamp noise, wiring and interconnection noise, media noise, etc. Early 78 rpm phonograph discs had a dynamic range of up to 40 dB, [24] soon reduced to 30 dB and worse due to wear from repeated play. Vinyl microgroove phonograph ...