- a capella
- vocal music without the accompaniment of instruments.
The property of a material that changes acoustic energy into
(usually) heat energy. A material or surface that absorbs sound
waves does not reflect them. Absorption of a given material is
frequency dependant as well as being affected by the size, shape,
location, and mounting method used.
see also absorption coefficient
A rating of a material that tells how much sound energy it absorbs
at given frequencies. Measured in Sabines.
see also Sabine
Alternating Current. Electrical current that changes its direction
of flow. Standard home power is 60HZ AC. This means the current
changes direction 60 times each second. Audio lines carry AC current.
see also DC; HZ; Hertz
Electrical circuits which require external power to operate.
Circuits using transistors, integrated circuits and the like are
active circuits. A simple inline pad made of resistors is passive,
it doesn't require external power to operate.
see also passive circuitry
A device that takes a full-range audio signal and splits it into
2, 3, 4, or even 5 different segments. A simple 2-way crossover
provides an output for the lows and an output for the highs. Usually
a control is given which allows the user to select what the crossover
point will be. The outputs then feed separate amplifiers and speakers.
This method provides better crossover linearity and power usage.
see also passive crossover
Americans with Disabilities Act. Specifically as it pertains
to sound, an act of Congress which states that all public meeting
facilities (exempting religious and federal) be equipped with
approved listening assistive or "hearing impaired" services/devices.
When two or more connectors do not mate physically, an adapter
permits the connection to be made. There are hundreds of different
combinations of adapters available.
After Fade Listen. The function of a button found on the input
channels of a mixer. Engaging this feature causes the signal found
after the channel fader to be routed to a special headphone circuit
(typically). This circuit allows the operator to listen to the
post (or after) fader signal separate from the rest of the mix.
see also PFL; solo
A scale of the percentage of the articulation loss of consonants.
A formula derived by V.M.A. Peutz based on distance, RT60, Volume
of air in the room, the N factor, and the Q of the source. A measure
of how difficult it is to understand someone in a room. The lower
the number, the better for speech intelligibility.
The amount of noise in a room without any primay sound. The background
noises in a room (HVAC, traffic noise, etc.).
A device that increases the power of a signal. An audio power
amplifier takes the small mic or line-level signal and raises
it so it can power the speakers.
An signal that's made up of an infinite number of levels between
it's highest and lowest point. An analog recording is a recording
(storage) of the continuously changing electrical voltages. Conventional
cassette and video recordings are analog, whereas a CD is digital.
see also digital
American National Standards Institute. Organization that sets
the standards used for U.S. audio & visual equipment.
A piece of wire that can be flat or round, rigid or flexible,
hidden or visible that picks up (recieves) or sends (transmits)
radio waves in the air.
A device that electronically splits an antenna signal to feed
several receivers. This way, several receivers can share the same
antenna or set of antennas (assuming they all use a similar antenna
One of three tiny bones in the middle ear that helps transmit
sound waves from the outer ear to the cochlea.
see also hammer, stirrup
American Standard Code for Information Interchange. A standard
code in which alphabetic, numeric, and special characters are
symbolized by a 7-bit number. The number is made up of 0's and
On an audio mixer, to route the audio signal to a particular
place. For example, assigning a microphone channel to subgroup
1. Usually in the form of a switch and/or a pan-pot.
assistive listening system
Any device (except for a hearing aid) which helps a hearing impaired
person. This can be in the form of a wired pair of headphones,
FM wireless headphones, infrared receiver with headphones, etc.
The signal sent to the headphones is as direct as possible--that
is, extraneous noises and room reverberations are not accepted.
Usually a direct feed from the house mixer is used to feed such
A drop in signal level. Opposite of amplifying a signal, an attenuated
signal has had a drop in signal strength.
A device that controls the amplitude of a signal. Sometimes refered
to as a volume control. Common examples are the gain control on
a mixer, or the fader on a mixer.
A series of audio equipment that's interconnected. A simple sound
reinforcement audio chain would be as follows: microphone, mixer,
equalizer, amplifier, speaker.
audio spectrum analyzer
Piece of equipment that lets you have a visual look at the power
level of a sound at different frequencies. Often called a real-time
analyzer as it lets you look at the sound as it's happening. Units
display information at 1/3-octave bands typically, but some equipment
can show up to 1/12-octave resolution or finer.
A mixer that can be set so microphones are automatically turned
on when a specified amount of sound level is reached at the microphone.
Auto-mixers can also include controls which allow one microphone
to have priority over the others. This feature would be used for
the main microphone so the person in charge can interrupt anyone
A control on a mixer input channel that allows a signal separate
from the main signal to feed other equipment. Such uses include
an auxiliary feed for tape recording, monitor mixes, and assistive
listening systems. The use of an auxiliary send allows the user
to create different mixes for each send which are separate from
the main mix.
American Wire Gauge. National standard for measuring a wire's
conductor size. The smaller the number, the larger the wire size
(12AWG is larger than 18AWG).
The point horizontally and vertically centered in front of a
microphone or speaker. Certain microphones have different frequency
response curves at different points off-axis. A speaker's directivity
is measured off axis. Microphones and speakers typically behave
differently off axis than they do on axis.