Peak-to-peak (sometimes abbreviated as p-p) amplitude (V PP) refers to the total voltage swing of a signal, which is double the peak amplitude of the signal. A signal at +4 dBu is equivalent to a sine wave signal with a peak amplitude of approximately 1.736 volts, or any general signal at approximately 1.228 V RMS. Įxpressed in absolute terms, a signal at −10 dBV is equivalent to a sine wave signal with a peak amplitude (V PK) of approximately 0.447 volts, or any general signal at 0.316 volts root mean square (V RMS). For consumer equipment it is −10 dBV, which is used to reduce manufacturing costs. #LINEIN MP3 PROFESSIONAL#The most common nominal level for professional equipment is +4 dBu (by convention, decibel values are written with an explicit sign symbol). Modern audio equipment does not use 600 Ω matched loads, hence dBm unloaded ( dBu). 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 ( dBm). 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). The decibel volt reference voltage is 1 V RMS = 0 dBV. 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 nominal level and the reference voltage against which it is expressed depend on the line level being used. time of sine waves at reference and line levels, with V RMS, V PK, and V PP marked for the +4dBu line level.Ī line level describes a line's nominal signal level as a ratio, expressed in decibels, against a standard reference voltage. Professional equipment may also use unbalanced connections with (1/4 inch) TS phone jacks. Professional equipment commonly uses balanced connections on 6.35 mm (1/4 inch) TRS phone jacks or XLR connectors. The line in/out connections on consumer-oriented audio equipment are typically unbalanced, with a 3.5 mm (0.14 inch, but commonly called "eighth inch") 3-conductor TRS minijack connector providing ground, left channel, and right channel, or stereo RCA jacks. Line out provides an audio signal output and line in receives a signal input. The "strength" of these various signals does not necessarily refer to the output voltage of the source device it also depends on its output impedance and output power capability.Ĭonsumer electronic devices concerned with audio (for example sound cards) often have a connector labeled line in and/or line out. There are weaker signals such as those from microphones ( microphone level or mic level) and instrument pickups ( instrument level), and stronger signals, such as those used to drive headphones and loudspeakers ( speaker level). Line level sits between other levels of audio signals. Line level is the specified strength of an audio signal used to transmit analog audio between components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles. For the tool of a similar name, see Spirit level.
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