Recording Microphones - Technical Terms

Capsule

A term describing the housing for the diaphragm or diaphragms (two are needed to create a cardioid response).

D.I. box

This can be a 'passive' (transformer based) or 'active' (powered) device that converts the high impedance signal from electric bass, guitars and keyboards into a low impedance signal that audio mixers require. They also have an output that goes to the musician's amplifier which can be mic'd up as well.

Diaphragm

This is either a thin film of mylar plastic (coated in a thin film of metal) stretched over a lightweight frame that is exposed to the sound source, or in the case of ribbon microphones a thin metal strip.

Digital

A means of sampling an analogue waveform against time and representing this signal as binary code, the advantage of Digital Audio is that the sound quality doesn’t degrade as it is copied. A digital copy is called a ‘clone’.

Distortion

A recorded sound does not sound like the original, this is usually due to excessive gain being applied to any of the electrical circuits that the audio passes through, so for example a greatly amplified sine wave has its peaks flattened and it now resembles a square wave.

Electro-magnetic fields

These are generated by high voltage and current devices e.g. Power transformers, televisions and computer monitors, they are alternating currents so they send out an electrical signal which can be picked up by microphones and their cables if they are in close proximity.

E.Q.

Short for Equalisation, it refers to the use of boost or cut circuits for different frequency bands. At its most basic this is bass, middle and treble but it can involve many smaller frequency bands, the most commonly known version of this is a Graphic Equaliser.

Feedback

Sound from a microphone is amplified by speakers which goes back into the microphone again. If the level of this sound is too high then an acoustic ‘howl-round’ or ‘feedback’ is created, usually at one particular frequency.

Frequency

Sound consists of waves of air being alternately pushed and pulled many times a second by the sound source. This is measured in Hertz (Hz) and Kilohertz (Khz), there are 1000 hertz in a kilohertz. Human hearing in young children is considered to be from 20Hz to 20Khz. The frequencies lower than 20Hz we feel rather than hear if they are loud enough, as we become adults the top frequencies we hear go down to typically 15khz.

Gain

This is part of the amplification circuitry, it adds extra ‘volume’ to the signal.

Impedance

The equivalent of resistance in alternating current circuitry Failure to properly match each device’s impedance results in a thin sound (no bass) and possibly distortion.

Mixer

A device that accepts two or more audio sources, each channel has a gain control and a volume fader to allow balancing their respective levels. In addition pan controls, equalisation and an output limiter are often incorporated.

Pan

This used to be just a switch but more usually is a variable control that moves the apparent position of a mono audio source to ‘left’, ‘centre’ and ‘right’ and inbetween positions of a stereo panorama.

Pad

A resistor circuit (attenuator) that reduces the amount of electrical current being passed on.

Phase

Audio and Radio waves can bounce off hard materials, this can result in a wave arriving at a microphone or antenna at slightly different times, this means the positive part of the wave arrives at the same time as the negative part of the wave and they cancel each other out.

Plosives

Short blasts of wind from a person speaking or singing. Words beginning with ‘B’, ‘P’ and ‘T’ are the worst culprits, it sounds like a large bass rumble and overwhelms the wanted audio momentarily. A 'pop' shield is often used to help control and soften plosives before they hit the microphone.

Polar response (pick-up pattern or directional sensitivity of the microphone)

Omni, Cardioid, hypercardioid, figure of eight. The further away the line is from the centre, the more sensitive it is. Only one line of frequency response is shown here, typically at 1khz, however on a technical specifications sheet that comes with the microphone it will show the response at many frequencies, don't worry that the lower frequencies e.g. 100hz will tend towards omnidirectional, this is normal.

Splitter box

This can be a 'passive' (transformer based) or 'active' (powered) device that splits a microphone or other audio source into two separate identical feeds. This is useful when a P.A. system and a recording device both need to be fed. In the days before splitter boxes two separate microphones had to be put close to one another on one microphone stand for each sound source and sent to their respective destinations i.e. P.A. system and mobile recording truck.

Tone generator

This is built into an audio mixer, it is usually set at 1Khz and is used as a reference for setting recording levels of the recorder it is feeding.

Transducer

A general term that describes a device that converts audio information from one form to another e.g. microphone or speaker.

Transients

The initial attack phase of a new note or drum hit, this usually is the loudest part of the audio waveform.

Windshield

A fine meshed material that breaks down the blast of wind but lets sound waves pass through.

XLR

A 'balanced audio' connection protocol which helps to avoid picking up unwanted electro-magnetic interference. The X pin is connected to Earth, L goes to Live and R goes to Return.