PA: Public Address System

A PA system is a sound reinforcement system enabling live performances to be heard by an audience.

In its most basic form, it usually consists of a set of stage microphones connected to a mixing console or desk. A Live Sound engineer operates the console to balance and EQ the sound from the stage. The console outputs are sent to:

1. A Front of House (FOH) power amplifier and FOH speakers for the audience,
2. A Foldback system located on stage for the performers to hear themselves.

While large PA systems are much more complex than shown below, the basic layout of equipment is similar.

Graphic Equalisers are used where shown below, not to tweak the performers' sound, but to make the sound of the PA work with the acoustics of the room it is in.

Pad

A pad is an electrical circuit used to attenuate or reduce the amplitude of an audio signal by a fixed amount, e.g a -15dB pad reduces the signal by a fixed 15 decibels.

Some pads, such as the 'Bridge T', can provide attenuation without changing impedance. Circuit here

Pads can be built in to mixing consoles to allow for microphones of different outputs. They are also available as 'in-line' devices that can be inserted in a mic lead or signal cable.

Patchbay

A patchbay consists of a panel of jacks (female receptacles) hard-wired to all the inputs, outputs and side-chains of outboard equipment, and all the outputs and insert points of the mixing console.

Often used in recording studios to enable rapid connection of any combination of equipment by the use of 'patch cords', or 'patch leads'.

Power amplifier

A Power Amplifier is one without tone controls, and with a higher power output than a line amplifier or pre-amp.

In pro applications, the function of controlling tonal balance is performed by the mixing console that drives the amp.

By comparison, the typical integrated amplifier used for home hi-fi contains a pre-amp PLUS a power amp.

Commonly used to drive loudspeakers such as studio monitors and PA system speakers.

Proximity effect, sometimes just called proximity, is an increase in the bass response of certain mics as the distance between it and its sound source is decreased.

Whether this is a good thing or not depends on what you want. Close miking an instrument may produce an undesirable boost in the bass. Close miking a vocalist singing an intimate lyric can give a tonal warmth that adds to the production. In short, knowing it's going to happen gives you control over what you want to do with it.