Mackie SR24•4 Owner's Manual page 47

gain
Gain is the measure of how much a circuit
amplifies a signal. Gain may be stated as a ra-
tio of input to output values, such as a voltage
gain of 4, or a power gain of 1.5, or it can be
expressed in decibels, as a line amplifier with
a gain of 10dB.
gain stage
An amplification point in a signal path, ei-
ther within a system or a single device.
Overall system gain is distributed between the
various gain stages.
graphic EQ
A graphic equalizer uses slide pots for its
boost/cut controls, with its frequencies evenly
spaced through the audio spectrum. In a per-
fect world, a line drawn through the centers
of the control shafts would form a graph of the
frequency response curve. Get it? Or, the posi-
tions of the side dots give a graphic
representation of boost or cut levels across
the frequency spectrum.
ground
Ground is also called earth. Ground is de-
fined as the point of zero voltage in a circuit
or system, the point from which all other volt-
ages are measured. In electrical systems,
ground connections are used for safety pur-
poses, to keep equipment chassis and controls
at zero voltage and to provide a safe path for
errant currents. This is called a safety ground.
In computer and audio equipment, tiny
currents and voltages can cause noise in the
circuits and hamper operation. In addition to
providing safety, ground provisions in these
situations serve to minimize the pickup, de-
tection and distribution of these tiny noise
signals. This type of ground is often called
technical ground.
Maintaining a good safety ground is always
essential to prevent electrical shock. Follow
manufacturer's suggestions and good electri-
cal practices to ensure a safely grounded
system. Never remove or disable the ground-
ing pin on the power cord.
Quality audio equipment is designed to
maintain a good technical ground and also op-
erate safely with a good safety ground. If you
have noise in your system due to technical
grounding problems, check you manual for wir-
ing tips or call technical support. Never disable
the safety ground to reduce noise problems.
ground loop
A ground loop occurs when the technical
ground within an audio system is connected
to the safety ground at more than one place.
Two or more connections will allow tiny cur-
rents to flow in the loops created, possibly
inducing noise (hum) into the audio system.
If you have noise in your system due to ground
loops, check your manual for wiring tips or
call technical support. Never disable the
safety ground to reduce noise problems.
Haas effect
A psychoacoustic effect in which the time
of arrival of a sound to the left and right ears
affects our perception of direction. If a signal
is presented to both ears at the same time at
the same volume, it appears to be directly in
front of us. But if the signal to one ear, still at
the same volume, is delayed slightly (0 to 5
msec), the sound appears to be coming from
the earlier (non-delayed) side.
headroom
The difference between nominal operating
level and peak clipping in an audio system.
For example, a mixer operating with a nomi-
nal line level of +4dBu and a maximum
output level of +22dBu has 18dB of head-
room. Plenty of room for surprise peaks.
Hertz
The unit of measure for frequency of oscilla-
tion, equal to 1 cycle per second. Abbreviated
Hz. KHz is pronounced "kay-Hertz" and is an
abbreviation for kilohertz, or 1000 Hertz.
house
In SR parlance, "house" refers to the sys-
tems (and even persons) responsible for the
primary sound reinforcement in a given hall,
building, arena or "house." Hence we have the
house mixer or house engineer, the house
mix, the house mix amps, the main house
speakers and so on.
Hz
See Hertz.
impedance
The A.C. resistance/capacitance/induc-
tance in an electrical circuit, measured in
ohms. In audio circuits (and other AC cir-
cuits) the impedance in ohms can often be
much different from the circuit resistance as
measured by a DC ohmmeter.
Maintaining proper circuit impedance rela-
tionships is important to avoid distortion and
minimize added noise. Mackie input and out-
put impedances are set to work well with the
vast majority of audio equipment available.
impedance balanced
An audio circuit technique used to gain
much of the advantage of a fully balanced
Appendices
45