Echo
The reflection of sound from a surface. Reverberation and echo are terms that can be used interchangeably, but in pro audio a distinction is usu- ally made: echo is considered to be a distinct, recognizable repetition (or series of repetitions) of a word, note, phrase or sound, whereas rever- beration is a diffuse, continuously smooth decay of sound.
Effects unit
An external signal processors used to add reverb, delay, spatial or psy- choacoustic effects to an audio signal.
EIN (Equivalent Input Noise)
A specification that helps measure the noise generation of a gain stage.
Equalizer (EQ)
A device that allows the boosting or cutting of selected bands of fre- quencies in the signal path. In the form of tone controls or sliders.
Fader
A linear control providing level adjustment
Feedback
The “howling” sound caused by bringing a microphone too close to its associated loudspeaker.
Flanging
A modulation effect. Before digital delay effects units, the flanging effect could be accomplished by playing two tape machines in synchroniza- tion, then causing one tape to become slightly out of synch by rubbing a finger on the tape reel.
FOH
An acronym for Front Of House. Refers to the main stage to audience sound system.
Frequency
The number of times an event repeats itself in a given period. 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 amplifies a signal.
Gain stage
An amplification point in a signal path, either within a system or a single device.
Graphic EQ
A graphic equalizer uses slide pots for its boost/cut controls with its frequencies evenly spaced through the audio spectrum.
Ground
Also called earth. Ground is defined as the point of zero voltage in a cir- cuit or system, the reference point from which all other voltages are mea- sured. 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 elec- trical shock. Follow manufacturer’s suggestions and good electrical prac- tices to ensure a safely grounded system. Never disable the safety ground to reduce ground loop 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 cre- ated, 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 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 pre- sented 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 available signal range above the nominal level before clipping occurs.
Hertz (Hz)
Unit of measure for frequency of oscillation, equal to 1 cycle per second.
Highpass filter
A filter that rejects low frequencies.
Impedance
The A.C. resistance/capacitance/inductance in an electrical circuit. Impedance may not be purely resistance but is mesaured in ohms and is usually indicated by the omega symbol (Ω ).
Insert
A break point in the signal path to allow the connection of external devices, for instance signal processors.
Line level
A signal whose level falls between –10dBu and +30dBu.
Master
A control affecting the final output of a mixer. A mixer may have sev- eral master controls, which may be slide faders or rotary controls.
Mic level
The typical level of a signal from a microphone. A mic level signal is generally below –30dBu.
Mic preamp (mic-pre)
Short for microphone preamplifier. An amplifier that functions to bring the very low signal level of a microphone (approximately –50dBu) up to line level (approximately 0dBu). Mic preamps often have their own gain control to properly set the volume for a particular source. Setting the mic preamp gain correctly is an essential step in establishing good noise and headroom for your mix.
Monaural (MONO)
Monaural has to do with a signal which, for purposes of communicat- ing- audio information, has been confined to a single channel. One micro- phone is a mono pickup; many microphones mixed to one channe is a mono mix; a mono signal played through two speakers is still mono, since it only carries one channel of information. Several monaural sources, however, can be panned into a stereo mix. Monaural sound reinforce- ment is common for environments where stereo sound reinforcement would provide an uneven reproduction to the listener.
Monitor
In sound reinforcement, monitor speakers (or monitor headphones or in-the-ear monitors) are those speakers used by the performers to hear themselves. Monitor speakers are also called foldback speakers. In record- ing, the monitor speakers are those used by the production staff to listen to the recording as it progresses.
Monitor send, also (foldback)
A feed sent from the mixer back to the artist via loudspeakers or head- phones to enable them to monitor the sounds they are producing.
Noise floor
The residual level of noise in any system. In a well designed mixer, the
