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second, which gives us the sensation of pitch,
harmonics, tone and overtones. Frequency is
measured in units called Hertz (Hz). One Hertz
is one repetition or cycle per second.
gain
The measure of how much a circuit ampli-
fies a signal. Gain may be stated as a ratio of
input to output values, such as a voltage gain
of 4, or a power gain of 1.5, or it can be ex-
pressed in decibels, such as a line amplifier
with a gain of 10dB.
gain stage
An amplification point in a signal path,
either 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
positions of the slide pots give a graphic rep-
resentation of boost or cut levels across the
frequency spectrum.
ground
Also called earth. Ground is defined as the
point of zero voltage in a circuit or system, the
reference point from which all other voltages
are measured. In electrical systems, ground
connections are used for safety purposes, to
keep equipment chassis and controls at zero
voltage and to provide a safe path for errant
currents. This is called a safety ground.
Maintaining a good safety ground is always
essential to prevent electrical shock. Follow
manufacturer’s suggestions and good electrical
practices to ensure a safely grounded system.
Never remove or disable the grounding pin on
the power cord.
In computer and audio equipment, tiny cur-
rents 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, detec-
tion and distribution of these tiny noise
signals. This type of ground is often called
technical ground.
Quality audio equipment is designed to main-
tain a good technical ground and also operate
safely with a good safety ground. If you have
noise in your system due to technical grounding
problems, check your manual for wiring 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 currents to
flow in the loops created, possibly inducing
noise (hum) in the audio system. If you have
noise in your system due to ground loops,
check your manual for wiring tips or call tech-
nical 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 af-
fects 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 ear-
lier (non-delayed) side.
headroom
The difference between nominal operating
level and peak clipping in an audio system. For
example, a mixer operating with a nominal
line level of +4dBu and a maximum output
level of +22dBu has 18dB of headroom. 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 Sound Reinforcement parlance, “house”
refers to the systems (and even persons) re-
sponsible for the primary sound reinforcement
in a given hall, building, arena or “house.”
Hence we have the house mixer or house engi-
neer, the house mix, the house mix amps, the
main house speakers and so on.
Hz
See
Hertz.
impedance
The A.C. resistance/capacitance/inductance
in an electrical circuit, measured in ohms. In
audio circuits (and other AC circuits) the im-
pedance 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.
