Lexicon Line-In/Line-Out
Line-In and Line-Out are terms for high level inputs and outputs. In hi-fi equipment, these are the connections for Tuner, Tape Devices, CD Player, etc.
The characteristics of these inputs and outputs are specified in the standard IEC-61938 international standard, which does not necessarily mean that all manufacturers adhere to it. The standard specifies a Reference Level of 0.5V (-6dBV) and requires:
- Outputs have an outputimpedance of 2.2kohm maximum.
- Inputs have a minimum input impedance of 22kOhm and an overload immunity of at least 2.8V.
It depends on the type of device how the standard level is to be understood. For a tape player, for example, the standard level is reached when playing a calibration tape, for a CD player the standard level is defined as 12dB below the maximum level (i.e. -12dBFS). This means, in particular, that the standard level is not the highest allowed or technically possible level, but rather the level used in normal operation with good level control. The difference between the standard level and the maximum level is called Maximum Level Control or Headroom.
An older rule sets the reference level at -10dBV, which is still in use today as the standard level for consumer devices.
Some hi-fi equipment does not have high level outputs, and these are mainly record player and microphones. These must therefore be connected to special inputs of an amplifier, the signal is not suitable for high level inputs.
See also the Wikipedia articles: [Line level]