Hardware & signal path
Line level
Line level is the standard signal strength equipment sends between devices — a player into a mixer, a mixer into an amplifier. It is far stronger than a microphone or turntable signal, which need preamplifying first.
In practice
Wrong input setting, not wrong gain: a player into phono distorts at every setting on the knob.
Check the line/phono switch before touching a gain knob, on every channel, every time you meet unfamiliar equipment. The symptoms are unmistakable once you know them — almost no signal means a phono source in a line input, and distortion that gain will not fix means the reverse. If one channel needs far more gain than the others with everything set correctly, that is usually consumer gear at −10 dBV meeting professional gear at +4 dBu, and the fix is at the source device rather than the mixer. Set gains against the meters afterwards.
−10 dBV
Consumer line level
+4 dBu
Professional line level
~12 dB
The gap between them
Where these come from: Published audio standards, not catalog figures. For what we can measure, see setting the level once the input is right.
Why it matters
It is why the input selector on a mixer channel exists. A turntable outputs a signal thousands of times weaker than a player does, so plugging one into a line input gives you something almost inaudible, and plugging a player into a phono input gives you distortion at any gain setting.
The two nominal standards differ too. Consumer gear runs about −10 dBV and professional gear about +4 dBu, which is roughly 12 dB apart — enough that mixed equipment always seems to need one channel run much hotter than the rest.
Frequently asked
What is the difference between line level and phono level?+
Phono is a turntable signal, thousands of times weaker and needing equalisation as well as amplification. Line level is what everything else sends. The mixer switch selects between them.
Why is one channel much quieter than the others?+
Usually a phono source in a line input, or consumer gear at −10 dBV feeding professional gear at +4 dBu. Check the input switch before adding gain.
Can you plug a turntable into a line input?+
You can, but it will be barely audible and wrong in tone. Turntables need a phono preamp — either the mixer switch or an external one.
Related terms
Gain
Gain sets how hot a track arrives at the channel before anything else touches it. It is a correction for how the record was mastered, not a volume control for the room.
Balanced and unbalanced
A balanced connection carries the signal twice, once inverted, and cancels anything picked up along the way. An unbalanced one carries it a single time, so interference picked up by the cable stays in the signal.
RCA and XLR
RCA is the unbalanced two-channel connector on players, turntables and consumer gear. XLR is the balanced three-pin connector used for long runs and microphones, and it locks into place.
Audio interface
An audio interface converts between the digital signal inside software and the analogue signal a mixer or amplifier accepts. In a timecode rig it also converts the other way, digitising the control signal coming off the turntables.
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