Glossary – E
Early Reflections – The first sound waves that reach a listener’s ear after bouncing off a surface in the room, usually heard almost immediately after the initial sound. The first stage of reverberation.
Echo – The distinct repetition of an initial sound, caused by the reflection of the sound waves upon a surface. We recognize a sound as an echo when the distance between the source and the reflection is far enough apart that we can detect the time delay between one and the other. Essentially, reverberation is the combination of many echoes occurring too rapidly to hear each individually. In the studio, echoes can be reproduced acoustically or simulated by a digital signal processor.
Echo Chamber – An enclosed room designed with reflective, non-parallel surfaces for the purpose of creating acoustic echoes (reverberation).
Edit – To change one or more parameters of a recorded sound after the fact. This can take many forms, including “punching in” a section of the music that is re-recorded to replace the original version; altering the shape/size of waveforms graphically; changing the sequence of playback; and many others. Analog editing would typically involve splicing the magnetic tape on which the audio signals were recorded. These days, almost all editing in the studio is done via computer using a digital audio workstation (DAW).
Effects – 1) Various ways an audio signal can be modified by adding something to the signal to change the sound. 2) Short for the term Sound Effects (sounds other than dialogue, narration or music like door closings, wind, etc.) added to film or video.
Effects Track – 1) In film production audio, a recording of the mixdown of all the sound effects ready to be mixed with the dialogue and music. 2) In music recording, one track with a recording of effects to be added to another track of a multitrack recording.
Effects Processor – (Also called Guitar Processor) A device that adds audio effects to a direct guitar signal, such as reverb, chorusing, flanging, delay, overdrive, amplifier simulation, etc. Effects processors can occur as individual effects boxes or multi-sound pedal boards (see also “Foot Pedals,” “Foot Switches”) added into the signal path between the guitar and the console. They can also be found as presets in guitar amplifiers, or even as digital plug-ins within a DAW.
Electret – A dielectric plate that is designed with permanent polarity, allowing it to function similarly to a magnet. (“Electret” comes from the words “electricity” and “magnet.”) Used in some microphone types in place of a capacitor (condenser).
Electret Microphone – A variation of condenser microphone that uses an electret instead of a capacitor. (Also called “Electret Condenser Microphone.”) Because the electret is permanently polarized, an electret microphone does not require an external power source as a standard condenser microphone does.
Electromagnetic Field – (Abbreviated EMF) A field of magnetic energy put out because of current traveling through a conductor.
Electromagnetic Interference (EMI) – The bane of audio professionals everywhere, EMI is a type of interference caused by nearby electromagnetic activity, which can be picked up by audio cables and equipment, causing unwanted noise, hum or buzz in audio systems. Common causes of EMI in audio systems may include high-current power lines, fluorescent lighting, dimmer switches, computers, video monitors and radio transmitters.
Electrons – Negatively charged particles revolving around the nucleus of an atom. Electrical current is generated by electrons moving along a conductor, like a metallic wire.
Envelope – The collective term for the four elements of the lifespan of a sound: Attack, Decay, Sustain and Release (ASDR). The envelope of a sound describes how a sound or audio signal varies in intensity over a period of time.
Equal Loudness Contours – A drawing of several curves showing how loud the tones of different frequencies would have to be played for a person to say they were of equal loudness. (See also “Fletcher-Munson Curves.”)
Equalizer – An audio signal processor that uses one or more filters to boost or cut the amplitude (volume) of certain frequencies within the sound. The underlying principle is to balance or “equalize” the frequency response of the audio system, or to create balance between multiple signals in a sonic space. However, audio engineers may use equalizers to alter or “color” the sound in many different ways.
Expander – A signal processor (or plug-in) that performs the opposite function of a compressor, expanding the dynamic range of an audio signal rather than compressing it. It accomplishes this by further reducing the amplitude of signals that drop below a set threshold.
Expansion Ratio – The rate by which an expander attenuates an incoming signal, measured in decibels. For example, an expansion ratio of 2:1 means the expander will reduce the signal by 2dB for every 1dB it drops below the threshold. If the signal falls 3dB below the threshold, the expander attenuates it by 6 dB, and so on.