Line level
Overview
The term "line level" in audio refers to a signal voltage level that is standardized for use in connecting audio equipment. One example is the audio connection of a DVR to a television.
Basics
There are two primary reasons to standardize the voltage level for audio signals sent from one piece of equipment to another:
- To maximize the dynamic range
- To retain the dynamic range of the signal.
To maximize the dynamic range the signal voltage level must be high enough to allow the highest level signals to be a significantly louder than noise that is also present. It is physically impossible to make a "perfectly quiet" electronic circuit due to many factors including the random motion of electrons in components. As the voltage of the power supply is increased, the possible difference in level between the noise and the highest level signals is increased. But the noise level also tends to increase; so that there is a point of diminishing return.
Other factors such as circuit impedance and noise pick-up by cables also affect dynamic range; so line level signals are designed to provide good dynamic range in these conditions.
If the audio signal received is too high in level; distortion could occur if there is not some provision to "scale" the incoming signal to the operating range of the receiving device. Conversely; if the signal is too low; even with level compensation at the input of the receiving device, some of the dynamic range could be lost. The process of raising the lower level signal to match the receiving device's peak signal level will also increase the level of the noise. A close match in operating level between the output of the sending device and the input of the receiving device helps to ensure that the full dynamic range of the signal is retained.
Professional versus Consumer Line Level
Professional Line level
The vast majority of professional audio equipment has Balanced Line level Input and Output (I/O) with a peak level of +24dBu or +18dBu. Unbalanced line level typically has a peak level of +18dBu.
This make Professional Line level incompatible with most Consumer audio equipment for two reasons:
- Most consumer audio equipment has Unbalanced Line level I/O.
- The peak level is 6-12dB’s higher than Consumer Line level I/O.
Standard XLR to RCA adapters or adapter cables can be used to connect professional Line level outputs to consumer devices with the following considerations:
- The Professional Line output must operate Unbalanced. Lavry products require a setting to be changed for XLR outputs to operate unbalanced. Please refer the products operating manual for specifics.
- The output level must be reduced to match Consumer Line level. Lavry DA converters and Microphone Preamplifiers have Output level settings. Please refer the products operating manual for specifics.
Professional Line level I/O connections are typically made with XLR or T.R.S. connectors.
Consumer Line Level
Most Consumer Line audio equipment has Unbalanced Line level Input and Output (I/O) with a peak level of +8dBu, which equals +6dBV or 2Vrms. Consumer level is typically specified in Vrms or dBV.
Although Consumer Line level I/O is unbalanced, with relatively short cables and proper grounding the Consumer Line output signal can be connected to balanced Professional inputs if the receiving device has enough gain to raise the level the required amount. The Lavry AD10, AD11, LK-Solo, and LK-1 all have the gain required to raise Consumer Line level signals to Professional Line level.
Consumer Line Level I/O connections are typically made with RCA and T.S. connectors.