There are many things to consider, like the various signal levels, inputs & outputs, connectors…etc, etc. and the list goes on! It won't replace lots of hands on experience, but at least by learning some of the jargon you'll know the basics and not sound like a complete beginner!!

For the jaded road warrior, look at it as a refresher course on what all our sexy mumbo-jumbo actually means in the real world.

You might just remember something you forgot!!!

This time we'll continue with the A - Z of Live Audio looking at the 'Cs.'

CANNON: A manufacturer of electrical connectors who first popularised the three-pin connector now used universally for balanced microphone connections. (Also used for line level signals on high-end or pro gear.) In live sound, a Cannon connector is taken to mean a Cannon XLR-3 connector or any compatible connector.

CAPACITOR: An electronic device which stores an electrostatic charge, blocks the flow of direct current (DC), and permits the flow of alternating current (AC). Basically, a capacitor consists of two parallel metal plates insulated from each other by a dielectric. (A material in which an electric field can be sustained with a minimum dissipation of power.)

CAPACITOR MICROPHONE: A microphone that operates by measuring the change in electrical charge across a capacitor. One of the electrodes of the capacitor - a thin conductive membrane - forms the mic's diaphragm that flexes in response to changes in sound pressure.

CARDIOID : Literally means heart-shaped. In live-sound, 'cardioid' refers to the shape of the response or sensitivity pattern of some directional microphones. Cardioid mics pick-up sound better from the front (on-axis) than the back (off-axis).

CHANNEL: A single strip of controls on a mixing desk, relating to either a single input or a pair of main/monitor inputs. A functional path in an audio circuit: an input channel, an output channel, a recording channel, the left channel etc.

CHANNEL [MIDI]: Channel refers to one of 16 possible data channels over which MIDI data may be sent. Up to 16 different MIDI instruments or parts may be addressed using a single cable.

CHORD : Three or more different musical notes played at the same time.

CHORUS : Effect created by doubling a signal and adding delay and pitch modulation. Usually panned across a stereo field.

CHROMATIC : A scale of pitches rising in semitone steps.

CLICK TRACK : A metronome or pulse which assists musos to play in time!!

CLIPPING : Severe form of distortion which occurs when a signal attempts to exceed the maximum level which a piece of equipment is designed to handle. When seen on an oscilloscope, the audio peaks appear 'clipped off' or as a 'square wave'. [See also GAIN STAGE or DYNAMIC RANGE.]

CLUSTER : An array of loudspeakers or horns suspended above an audience to act as a single or point source of sound.

COINCIDENT : Two signals are said to be coincident when they correspond exactly, fall upon or meet at the same point, coinciding or occurring in space or time in exact agreement.

COMB FILTER : When two sound waves to be combined have different amplitudes, phases, and frequencies, the resulting soundwave develops many 'nulls' where the energy is cancelled. When a graphic image of the waveform is viewed, the resultant frequency response resembles a comb due to the nulls or 'notches' that have cancelled each other out.

COMMON MODE REJECTION : A measure of how effectively a balanced circuit rejects a signal that is common to both inputs. [See BALANCED ]

COMPANDER : Audio device that compresses a signal while encoding it, then expands it when decoding it.

COMPRESSOR : Device designed to reduce the dynamic range of audio signals by reducing the level of high signals or by increasing the level of low signals.

CONSOLE : Another term for a sound mixing desk.

CONDUCTOR : A wire, or cable that provides a low resistance path for electrical current to flow.

CONTINUOUS POWER : Also called 'RMS' power, it tells us the amount of power an amplifier can deliver when amplifying a constant, steady tone. It is usually measured at a signal frequency of 1000 Hz for a specific distortion, and is the most conservative (realistic!) statement of the capability of an amplifier. Continuous power in watts: W = V2/R [Power in watts equals the voltage squared, divided by the resistance of the load.]

CONTINUOUS PROGRAM MATERIAL : A signal, such as speech or music, that contains voltages continuously changing in both time and amplitude. (Frequency and voltage).

CONTOUR : Bass boost applied to signal to attain equal loudness at lower volumes.

CPS : 'Cycles-per-second' - an obsolete abbreviation for expressing frequency The term 'CPS' has been replaced by 'Hertz'. Hertz = cycles per second, named after the scientist who first described sound in terms of 'waves.'

CREST FACTOR : The ratio of the 'Peak' value to the RMS value. Musical signals can have peaks many times higher than the RMS value. The larger the high-transient peaks, the larger the crest factor.

CRITICAL DISTANCE : The point within a room where the direct sound is equal in intensity or level to the room sound. IE. Where the PA sound = the room/ambient sound.

CROSSOVER (X-OVER) : An active or passive electronic device that is used to separate an audio signal into two or more frequency bands above and below the crossover point.

Cross-over points are designed so that the speakers overlap by one Octave, so that the sounds produced by each can blend together. When operating Variable Crossovers make sure the cross-over points are placed outside the Vocal Range or Presence Frequencies, to maximise the systems clarity and punch. [See Important Frequency Sections for Tuning FOH.]
As there is a 3db increase where the bands overlap @ the crossover point, the greater the roll-off at the crossover frequency, measured in dB/octave, the better.

CROSSOVER ACTIVE : Active Crossovers split the sound into bands before the amps and only selected sound bands are sent to specifically designed speaker cabinets. [IE The signal is split at line-level.] Active crossover's contain an amplifier circuit and therefore require power. As all electrical circuits suffer signal loss, an active crossover enables any losses to be compensated for before being sent to the power amps. This results in the higher efficiency and output of active crossover systems - at the expense of extra cost, amps and weight that are required for each frequency band and not just for each speaker.

CROSSOVER PASSIVE : They are also called 'high-level' crossovers as the signal is at a 'high level', coming straight from the power amps. A passive crossover is built into most speaker cabinets in order to separate bands of frequencies from the full range speaker level signal

CROSSTALK : A common specification for mixing desks and other multi-channel gear which measures the interaction between adjoining channels or circuits. Crosstalk can be induced electromagnetically or electrostatically.

CURRENT : (I) The rate of flow of electricity in a conductor or circuit- measured in amperes. The amount of current that flows is determined by the voltage or electrical pressure applied and the resistance or opposition to current flow.

CUT : A term used to indicate the reduction in gain - attenuation - of a frequency or band of frequencies when equalizing an audio signal.

CUTOFF FREQUENCY : The frequency in a filter circuit above or below which cut or attenuation begins.

CYCLE : One complete vibration of a sound source or its electrical equivalent, in units per second. The cycle consists of the complete wave motion from the start position to the peak, to the trough and back to the start again. One cycle per second is expressed as 1Hertz (Hz).

Next time we'll look at …the 'Ds'.

In the meantime, if you've got any audio questions give me a yell, send me an email or post a message on roadtalkz. I'm not the font of all knowledge, but if I don't know the answer to your questions, I know enough guru's who will!!

See-ya-later.

Willy T.

Email : willyt-downunderdesk@roadogz.com

This is extracted from the book: "LIVE-AUDIO WORKSHOP: A Hands-on Guide to Rigging and Operating PA Systems." ISBN 0 646 36408 1. © Giraffe Communications 1998. Order via e-mail or at all good Music & Book shops.