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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]
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 ...
A-weighted SPL measurements of noise level are increasingly to be found on sales literature for domestic appliances such as refrigerators and freezers, and computer fans. Although the threshold of hearing is typically around 0 dB SPL, this is in fact very quiet indeed, and appliances are more likely to have noise levels of 30 to 40 dB SPL.
For example, for a 20 kHz analog audio sampled at 4× oversampling with second-order noise shaping, the dynamic range is increased by 30 dB. Therefore, a 16-bit signal sampled at 176 kHz would have a bit depth equal to a 21-bit signal sampled at 44.1 kHz without noise shaping. Noise shaping is commonly implemented with delta-sigma modulation.
Dynamic range in analog audio is the difference between low-level thermal noise in the electronic circuitry and high-level signal saturation resulting in increased distortion and, if pushed higher, clipping. [23] Multiple noise processes determine the noise floor of a system.
dBc (decibels relative to the carrier) is the power ratio of a signal to a carrier signal, expressed in decibels.For example, phase noise is expressed in dBc/Hz at a given frequency offset from the carrier. dBc can also be used as a measurement of Spurious-Free Dynamic Range between the desired signal and unwanted spurious outputs resulting from the use of signal converters such as a digital ...
The symbol dBrn or dB(rn) is an abbreviation for decibels above reference noise.. Weighted noise power in dB is referred to 1.0 picowatt.Thus, 0 dBrn = -90 dBm.Use of 144 line, 144-receiver, or C-message weighting, or flat weighting, can be indicated in parentheses.
It is often possible to reduce the noise by controlling the environment. Internal electronic noise of measurement systems can be reduced through the use of low-noise amplifiers. When the characteristics of the noise are known and are different from the signal, it is possible to use a filter to reduce the noise.