- Line level
Line level is a term used to denote the strength of an audio signal used to transmit analog sound information between audio components such as CD and
DVD players,TV s,audio amplifier s, andmixing console s, and sometimesMP3 player s.In contrast to line level, there are weaker audio signals, such as those from
microphone s and instrument pickups, and stronger signals, such as those used to driveheadphones andloudspeaker s. The strength of the various signals does not necessarily correlate with the output voltage of a device; it also depends on the source'soutput impedance , or the amount of current available to drive different loads.Nominal levels
A line level describes a line's nominal signal level as a ratio, expressed in
decibel s, against a standard reference voltage. The nominal level and the reference voltage against which it is expressed depend on the line level being used. While the nominal levels themselves vary, only two reference voltages are common: Decibel volts (dBV) for consumer applications, and decibels unloaded (dBu) for professional applications.The reference voltage for the decibel volt (0 dBV) is 1 VRMS, which is the voltage required to produce 1 milliwatt (mW) of power across a 1 kilohm (kΩ) load [ [http://www.tangible-technology.com/audiobasics/levels/level.html#SIDEBAR__calculating_dB_and_Power Tangible Tech Audio Basics] ] . The reference voltage for the decibel unloaded (0 dBu) is the voltage required to produce 1 mW of power across a 600 Ω load (approximately 0.7746 VRMS)cite book|title=Handbook for Sound Engineers: The New Audio Cyclopedia, Second Edition|editor=Glenn M. Ballou|year=1998|publisher=Focal Press|id=ISBN 0-240-80331-0|pages=pp. 761] .
The most common nominal level for consumer audio equipment is −10 dBV, and the most common nominal level for professional equipment is 4 dBu. By convention, nominal levels are always written with an explicit sign symbol. Thus 4 dBu is written as +4 dBu.
Expressed in absolute terms, a signal at −10 dBV is equivalent to a
sine wave signal with an amplitude of approximately 0.447 volts, or any general signal at 0.316 voltsroot mean square (VRMS). A signal at +4 dBu is equivalent to a sine wave signal with an amplitude of approximately 1.737 volts, or any general signal at approximately 1.228 VRMS.Line level in traditional signal paths
Acoustic sounds (such as voices or a
musical instrument s) are often recorded withtransducer s (microphone s and pickups) that produce weak electrical signals. These signals must be amplified to line level, where they are more easily manipulated by other devices such as mixing consoles and tape recorders. Such amplification is performed by a device known as apreamplifier or "preamp". After manipulation at line level, signals are then typically sent to a device known as a power amplifier, where they are amplified to levels that can driveheadphone s orloudspeaker s, which convert the signals back into sounds that can be heard through the air.Most
phonograph s also have a low output level and require a preamp; typically, a home stereo amplifier will have a specialphono input with a built-in preamp, which is much more sensitive than a standard, line-level input. The built-in phono preamp also accounts for theRIAA equalization curve resident to phonograph recordings.See also
*
Nominal level
*Alignment level References
External links
* [http://www.sengpielaudio.com/calculator-db-volt.htm Conversion of dBu to volts, dBV to volts, and volts to dBu, and dBV]
* [http://www.sengpielaudio.com/calculator-volt.htm Conversion of voltage V to dB, dBu, dBV, and dBm]
* [http://www.mmproductions.co.uk/faqgen5.html Units dBV in consumer equipment, dBu in professional equipment]
* [http://www.sizes.com/units/decibel.htm The Decibel]
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