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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 ...
dBm or dB mW (decibel-milliwatts) is a unit of power level expressed using a logarithmic decibel (dB) scale respective to one milliwatt (mW). It is commonly used by radio, microwave and fiber-optical communication technicians & engineers to measure the power of system transmissions on a log scale , which can express both very large and very ...
The unit dB FS or dBFS is defined in AES Standard AES17-1998, [13] IEC 61606, [14] and ITU-T Recs. P.381 [15] and P.382, [16] such that the RMS value of a full-scale sine wave is designated 0 dB FS. This means a full-scale square wave would have an RMS value of +3 dB FS.
For very low-power systems, such as mobile phones, signal strength is usually expressed in dB-microvolts per metre (dBμV/m) or in decibels above a reference level of one milliwatt . In broadcasting terminology, 1 mV/m is 1000 μV/m or 60 dBμ (often written dBu).
Minimum terrestrial analog-TV RF antenna signal (35 dB[μV]) [6] [7] [8] 10 −4: 500–1000 μV Miniature endplate potentials, spontaneous fluctuations in neuron potentials [1] 10 −3: 1–2 mV Potential created at ambient temperatures from K Type Thermocouple: Centi-10 −2 ~10–50 mV Ripple voltage in the output of a good DC power supply ...
A gain greater than one (greater than zero dB), that is, amplification, is the defining property of an active device or circuit, while a passive circuit will have a gain of less than one. [ 4 ] The term gain alone is ambiguous, and can refer to the ratio of output to input voltage ( voltage gain ), current ( current gain ) or electric power ...
Vinyl microgroove phonograph records typically yield 55-65 dB, though the first play of the higher-fidelity outer rings can achieve a dynamic range of 70 dB. [25] German magnetic tape in 1941 was reported to have had a dynamic range of 60 dB, [26] though modern-day restoration experts of such tapes note 45-50 dB as the observed dynamic range. [27]
A signal is applied to the input such that the output increases by 12 dB. The level of the signal needed to produce this is noted. In this case, it was found to be 0.25 microvolts. According to the radio designer, intelligible speech can be detected 12 dB above the receiver's noise floor (noise and distortion).