Brooks RM 909 reviews Envelope

1) How a sound or audio signal varies in intensity over a time span.
2) How a control voltage varies in level over time controlling a parameter of something other than gain or audio level.

FOH (Front of House)
Refers to the speakers that face toward the audience. Also called the "main" speakers.

Brooks Hi Fi reviews Clean
Describes a distortion free sound with few effects.

Far Field
The area from 3 feet away from the sound source up to the critical distance.

Brooks RM 909 Hi-Z
An abbreviation of the term High Impedance (Impedance of 5000 or more ohms).

Amplitude
The extreme range of a signal. Usually measured from the average to the extreme.

Action
In guitar playing, action refers to how far the strings sit off of the guitar neck. When strings are close to the neck, it is referred to as "Low Action". When the string sit far above the neck, it is called "High Action". Guitars with low action are easier to play, but make sure they are not too close, or it could causing buzzing.

Group Faders
The VCA faders of individual channels that are all controlled by a Group Master Fader (a slide control used to send out a control voltage to several VCA faders in individual channels).