Introduction

This article gives a simple overview of the process. Although most people without a technical understanding will connect guitars, keyboards and microphones to a mixer channel successfully, it can be helpful to understand the underlying principals to ensure you are maximising dynamic range and therefore signal quality.

Why follow a procedure?

When plugging a sound source into a mixer input channel we must follow a safe procedure. This is for a number of reasons ...

To ensure the signal does not overload the channel circuitry/exceed the dynamic range (and cause distortion)
To ensure the signal is not so quiet as to be effected by any hiss or noise in the channel circuitry
To avoid damaging the speakers
To avoid damaging our hearing
To avoid damaging a microphone

Mic and line level signals

In the studio the difference between the quietest and the loudest source signals can be huge.

Mic level

Mic level signals are very QUIET (up to 0.0775 volts or -20dBu) and are produced by ...

Microphones
Electric guitars & basses
Record players (phono)

Line level

Line level signals are very LOUD (up to 2.45 volts or +30dBu) and are produced by ...

Samplers
Synthesisers
Drum machines
Tape recorders
CD players
FX and outboard processors
Mixers
Soundcard's / audio interfaces
MiniDisc players
DAT recorders
etc

Mixer mic & line inputs

To accommodate the huge difference between Mic and Line signals, mixers have two input circuits, Mic Input and Line Input. The Mic input will be fed from an XLR/Canon socket. The Line input will be fed from a Jack socket.

A Mic/Line button will allow you to select the appropriate input for your source signal.

A gain control will allow you to turn down the signal so it doesn't overload the channel circuitry, a process known as "maximising the dynamic range" or "setting the best signal to noise ratio".

Maximising the dynamic range All equipment has dynamic range. This is the range between the quietest and loudest signals they can accommodate. A signal entering a mixer needs to be as loud as possible without overloading the circuitry and causing distortion.

Setting the best signal to noise ratio All circuits produce a fixed level of noise (hiss). If the source signal is loud enough this noise will be less noticeable.

mixer input channel diagram