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
CDA Compact Disc is an optical disc used to store digital data. It was originally developed to store sound recordings exclusively, but later it also allowed the preservation of other types of data. Audio CDs have been commercially available since October 1982...
and
DVDDVD, also known as Digital Versatile Disc or Digital Video Disc,is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage...
players, TVs,
audio amplifierAn audio amplifier is an electronic amplifier that amplifies low-power audio signals to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.The preceding stages in such a chain are low power audio amplifiers which perform tasks like...
s, and
mixing consoleIn professional audio, a mixing console, or audio mixer, also called a sound board or soundboard, is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...
s, and sometimes MP3 players.
In contrast to line level, there are weaker audio signals, such as those from
microphoneA microphone, colloquially called a mic or mike , is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1876, Emile Berliner invented the first microphone used as a telephone voice transmitter...
s and instrument pickups, and stronger signals, such as those used to drive
headphonesHeadphones are a pair of small loudspeakers, or less commonly a single speaker, with a way of holding them close to a user's ears and a means of connecting them to a signal source such as an audio amplifier, radio or CD player. They are also known as earphones, earbuds, stereophones, headsets or,...
and
loudspeakerA loudspeaker is an electroacoustic transducer that converts an electrical signal into sound. The speaker pulses in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.Loudspeakers are the most variable elements in a...
s.
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
CDA Compact Disc is an optical disc used to store digital data. It was originally developed to store sound recordings exclusively, but later it also allowed the preservation of other types of data. Audio CDs have been commercially available since October 1982...
and
DVDDVD, also known as Digital Versatile Disc or Digital Video Disc,is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage...
players, TVs,
audio amplifierAn audio amplifier is an electronic amplifier that amplifies low-power audio signals to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.The preceding stages in such a chain are low power audio amplifiers which perform tasks like...
s, and
mixing consoleIn professional audio, a mixing console, or audio mixer, also called a sound board or soundboard, is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...
s, and sometimes MP3 players.
In contrast to line level, there are weaker audio signals, such as those from
microphoneA microphone, colloquially called a mic or mike , is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1876, Emile Berliner invented the first microphone used as a telephone voice transmitter...
s and instrument pickups, and stronger signals, such as those used to drive
headphonesHeadphones are a pair of small loudspeakers, or less commonly a single speaker, with a way of holding them close to a user's ears and a means of connecting them to a signal source such as an audio amplifier, radio or CD player. They are also known as earphones, earbuds, stereophones, headsets or,...
and
loudspeakerA loudspeaker is an electroacoustic transducer that converts an electrical signal into sound. The speaker pulses in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.Loudspeakers are the most variable elements in a...
s. The strength of the various signals does not necessarily correlate with the output voltage of a device; it also depends on the source's
output impedanceThe output impedance is the impedance on the output of a circuit. This is sometimes also referred to as the internal resistance of the circuit....
, or the amount of current available to drive different loads.
Nominal levels
A line level describes a line's
nominal signal levelNominal level is the operating level at which an electronic signal processing device is designed to operate. The electronic circuits that make up such equipment are limited in the maximum signal they can output and the low-level internally-generated electronic noise they add to the signal...
as a ratio, expressed in
decibelThe decibel is a logarithmic unit of measurement that expresses the magnitude of a physical quantity relative to a specified or implied reference level. Since it expresses a ratio of two quantities with the same unit, it is a dimensionless unit...
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 V
RMS, which is the voltage required to produce 1
milliwattThe watt is a derived unit of power in the International System of Units . It measures rate of energy conversion. One watt is equivalent to 1 joule of energy per second....
(mW) of power across a 1
kilohmThe ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Simon Ohm.- Definition :...
(kΩ) load. 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 V
RMS).
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 waveThe sine wave or sinusoid is a function that occurs often in mathematics, music, physics, signal processing, audition, electrical engineering, and many other fields...
signal with an amplitude of approximately 0.447 volts, or any general signal at 0.316 volts
root mean squareIn mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
(V
RMS). 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 V
RMS.
Line levels and their nominal voltage levels.
| Use |
Nominal level |
Nominal level, VRMS |
Peak Amplitude, VPK |
ARDARD , is a joint organization of Germany's regional public-service broadcasters...
, Germany |
+6 dBu |
1.550 (approximate) |
2.192 (approximate) |
| USA professional audio |
+4 dBu |
1.228 (approximate) |
1.737 (approximate) |
| Consumer audio |
−10 dBV |
0.316 |
0.447 |
Line level in traditional signal paths
AcousticAcoustics is the interdisciplinary science that deals with the study of sound, ultrasound and infrasound . A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering...
sounds (such as
voiceIn music, a register is the relative "height" or range of a note, set of pitches or pitch classes, melody, part, instrument or group of instruments...
s or
musical instrumentA musical instrument is an object constructed or used for the purpose of making the sounds of music. In principle, anything that produces sound can serve as a musical instrument. The history of musical instruments dates back to the beginnings of human culture...
s) are often recorded with
transducerA transducer is a device, electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic, that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer .There are two kinds of transducers...
s (
microphoneA microphone, colloquially called a mic or mike , is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1876, Emile Berliner invented the first microphone used as a telephone voice transmitter...
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 a
preamplifierA preamplifier , or control amp in some parts of the world, is an electronic amplifier which precedes another amplifier to prepare an electronic signal for further amplification or processing...
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 drive headphones or
loudspeakerA loudspeaker is an electroacoustic transducer that converts an electrical signal into sound. The speaker pulses in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.Loudspeakers are the most variable elements in a...
s, which convert the signals back into sounds that can be heard through the air.
Most
phonographThe record player, phonograph or gramophone was the most common device for playing recorded sound from the late 1870s until the late 1980s.- Terminology :...
s also have a low output level and require a preamp; typically, a home stereo amplifier will have a special
phono inputThe phono input is a set of RCA input jacks, usually behind a stereo receiver to which a phonograph or turntable is attached. Modern phonograph needles and phono cartridges output a very low level signal, which is input to the receiver then amplified and equalized.Phonograph recordings are made...
with a built-in preamp, which is much more sensitive than a standard, line-level input. The built-in phono preamp also accounts for the
RIAA equalizationRIAA equalization is a specification for the correct playback of gramophone records, established by the Recording Industry Association of America...
curve resident to phonograph recordings.
External links