Line level
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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, TVs, audio amplifiers, and mixing consoles, and sometimes MP3 players.
In contrast to line level, there are weaker audio signals, such as those from microphones and instrument pickups, and stronger signals, such as those used to drive headphones and loudspeakers. 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 impedance, or the amount of current available to drive different loads.
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[edit] Decibels
Depending on the application, line levels are stated as voltage ratios expressed in decibels. These ratios are relative to different reference voltages in units of either decibel volts (dBV) or decibels unloaded (dBu).
Consumer audio equipment line levels are rated in dBV, and the most commonly used nominal level for such equipment is −10.00 dBV, which corresponds to a sine wave of about 0.3162 root mean square volts (VRMS). The absolute reference voltage is 1.000 VRMS.[1] This reference voltage represents 1.000 milliwatt (mW) at 1.000 kilohm (kΩ).
Professional audio equipment line levels are rated in dBu, and the most commonly used nominal level for such equipment is +4.000 dBu, which corresponds to a sine wave of about 1.228 VRMS. The absolute reference voltage is 0.7746 VRMS. This reference voltage corresponds to 1.000 mW of power at 600 Ω.
| Ratio | VRMS |
|---|---|
| +4 dBu (USA) | 1.228 V |
| −10 dBV (Homerecording) | 0.3162 V |
| +6 dBu (ARD, Germany) | 1.55 V |
[edit] Line-level in traditional signal paths
Acoustic sounds (such as voices or a musical instruments) are often recorded with transducers (microphones 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 preamplifier 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 loudspeakers, which convert the signals back into sounds that can be heard through the air.
Most phonographs also have a low output level and require a preamp; typically, a home stereo amplifier will have a special phono 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 the RIAA equalization curve resident to phonograph recordings.
[edit] See also
[edit] References
[edit] Bibliography
- (1998) in Glenn M. Ballou: Handbook for Sound Engineers: The New Audio Cyclopedia, Second Edition. Focal Press. ISBN 0-240-80331-0..
