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: 1.) To maximize the dynamic range 2.) 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 because the process of raising the lower level signal to match the receiving device's highest signal level will also increase the level of the noise. Having a reasonably 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.