A very steep low-pass filter used to limit the frequency range of an analogue signal prior to A/D conversion, so that the maximum frequency does not exceed half the sampling rate. (See A-D Conversion)

A system for synthesizing sounds by means of analogue circuitry, usually by filtering simple repeating waveforms.

The origin of the term is that the electrical audio signal inside a piece of equipment can be thought of as being ‘analogous’ to the original acoustic signal. Analogue circuitry uses a continually changing voltage or current to represent the audio signal. (cf. Digital)

The waveform signal level. It can refer to acoustic sound levels or electrical signal levels.

An Amplifier is an electrical device that typically increases the voltage or power of an electrical signal. The amount of amplification can be specified as a multiplication factor (eg. x10) or in decibels (eg. 20dB).

Unit of electrical current (eg. 13A). (See AC and DC)

A description of sound reflections in a confined space which add to the original direct sound. Ambience may also be created electronically by some digital reverb units. The main difference between ambience and reverberation is that ambience doesn't have the characteristic long delay time of reverberation; the reflections mainly give the sound a sense of space and the room a sonic character.

When an analogue signal is sampled for conversion into a digital data stream, the sampling frequency must be at least twice that of the highest frequency component of the input signal. If this rule is disobeyed, the sampling process becomes ambiguous as there are insufficient points to define each cycle of the waveform. This resulting in unwanted anharmonic distortion component frequencies (not musically related) being added to the wanted signal.

A sequence of instructions describing how to perform a specific task. Algorithms are often implemented in a computer language and compiled into a computer program. In the context of effects units, algorithms usually describe a software building block designed to create a specific effect or combination of effects.

A means of generating a control signal in a synthesizer based on how much pressure is applied to the keys of a MIDI keyboard. Most instruments that support this do not have independent pressure sensing for all keys ('polyphonic aftertouch'), but rather detect the overall pressure by means of a sensing strip running beneath the keys. Aftertouch is typically used to control such functions as vibrato depth, filter brightness, loudness and so on.