What is line level? | Basic Pro Audio Concepts

THE GIST

Line level is the standard signal strength at which most audio equipment is designed to operate. Lower-level microphone and instrument signals must be brought up to line level with a preamp before interfacing with most equipment. These line level signals are then further amplified to drive speakers and headphones for playback. There are two common standards for line level: +4dBV for professional audio equipment and -10dBu for consumer-level products.

Purpose

Because input voltages from microphones, preamps, DIs, and instrument outputs can differ dramatically in level, they must be adjusted to a common level for use in other equipment such as mixers, recorders, and signal processors. Once at line level, these signals can be processed and recorded with minimal noise and optimal fidelity.

Universal Audio Apollo 8 Quad with four mic pres

Preamps boost weak signals like microphones and guitars up to line level, while line trims allow finer adjustment of powerful signals from synthesizers or drum machines. Upon playback, power amplifiers are required to boost the signal enough to drive speakers or headphones.

While the terms “balanced” and “unbalanced” are often attached to +4dBu and -10dBV line levels, balancing is actually a technique for reducing noise and is not related to line level.

Professional vs. Consumer Line Level

As technology and the music industry evolved, two main standards for line level were established: +4dBu for “professional-grade” equipment, and -10dBV for “consumer-level” gear. As indicated by their suffixes, these two standards are measured against different reference voltages. While the history behind these two levels is a convoluted tale of changing impedance standards, the takeaway is simple: professional gear runs hotter.

Black Rooster Audio Magnetite Tape Saturator

The dBV (Volts) unit of measurement is derived from an early telephone standard, where 0dBV equals one volt. -10 on this scale comes out to about .316 volts, a relatively weak signal. The more modern dBu (unloaded) standard also measures voltage, but by a different calculation: 0dBu equals .775 volts. Therefore, +4 on the dBu scale equals 1.228 volts, a considerably stronger signal.

Devices specified to operate at either of these standards will perform best and should only receive input signals at the proper line level for the least amount of distortion and noise. However, many modern devices feature a switch that can be set to +4 or -10—especially on “prosumer” products designed to interface with professional and consumer gear.

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