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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 ...
Many high-quality domestic speakers have a sensitivity between ~84 dB and ~94 dB, but professional speakers can have a sensitivity between ~90 dB and ~100 dB. An '84 dB' source would require a 400-watt amplifier to produce the same acoustical power (perceived loudness) as a '90 dB' source being driven by a 100-watt amplifier, or a '100 dB ...
The decibel unloaded reference voltage, 0 dBu, is the AC voltage required to produce 1 mW of power across a 600 Ω impedance (approximately 0.7746 V RMS). [2] This awkward unit is a holdover from the early telephone standards, which used 600 Ω sources and loads, and measured dissipated power in decibel-milliwatts .
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 ...
Though the values vary widely between units, a typical analogue cassette might give 60 dB, a CD almost 100 dB. Most modern quality amplifiers have >110 dB dynamic range, [6] which approaches that of the human ear, usually taken as around 130 dB. See Programme levels. Phase distortion, Group delay, and Phase delay
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For example: an amplifier with a PSRR of 100 dB in a circuit to give 40 dB closed-loop gain would allow about 1 millivolt of power supply ripple to be superimposed on the output for every 1 volt of ripple in the supply. This is because = .