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dB(K) – decibels relative to 1 K; used to express noise temperature. [67] dB K⁻¹ or dB /K dB(K⁻¹) – decibels relative to 1 K⁻¹. [68] — not decibels per Kelvin: Used for the G / T (G/T) factor, a figure of merit used in satellite communications, relating the antenna gain G to the receiver system noise equivalent temperature T.
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]
A-weighted decibels are abbreviated dB(A) or dBA. When acoustic ( calibrated microphone) measurements are being referred to, then the units used will be dB SPL ( sound pressure level ) referenced to 20 micropascals = 0 dB SPL.
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]
OSHA's PEL for noise exposure is 90 decibels (dBA) for an 8-hour TWA. Levels of 90-140 dBA are included in the noise dose. [4] PEL can also be expressed as 100 percent “dose” for noise exposure. When the noise exposure increases by 5 dB, the exposure time is cut in half. [5] According to OSHA, a 95dBA TWA would be a 200 percent dose. [6]
The noise power from a simple load is equal to kTB, where k is the Boltzmann constant, T is the absolute temperature of the load (for example a resistor), and B is the measurement bandwidth. This makes the noise figure a useful figure of merit for terrestrial systems, where the antenna effective temperature is usually near the standard 290 K ...
If the pressure-to-intensity ratio is large then even a small phase mismatch will lead to significant bias errors. In practice, sound intensity measurements cannot be performed accurately when the pressure-intensity index is high, which limits the use of p-p intensity probes in environments with high levels of background noise or reflections.
Substituting the definitions of SNR, signal, and noise in decibels into the above equation results in an important formula for calculating the signal to noise ratio in decibels, when the signal and noise are also in decibels: =,,.