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Glossary of Audio Terms: O - Q



OCTAVE: When a frequency or pitch is transposed up by one octave, its frequency is doubled.

OFF-LINE: Process carried out while a recording is not playing. For example, some computer-based processes have to be carried out off-line as the computer isn't fast enough to carry out the process in real time.

OHM: Unit of electrical resistance.

OMNI-DIRECTIONAL: Microphone which picks up sound equally from all directions.

OPEN CIRCUIT: A break in an electrical circuit that prevents current from flowing.

OPERATING SYSTEM: The basic software that enables a computer to load and run other programs.

OSCILLATOR: Circuit designed to generate a periodic electrical waveform.

OVERDUB: To add another part to a multitrack recording or to replace one of the existing parts.

OVERLOAD: To exceed the operating capacity of an electronic or electrical circuit. 



PAD: Resistive circuit for reducing signal level.

PAN POT: Control enabling the user of a mixer to move the signal to any point in the stereo soundstage by varying the relative levels fed to the left and right stereo outputs.

PARALLEL: A means of connecting two or more circuits together so that their inputs are connected together, and their outputs are all connected together.

PARAMETER: A variable value that affects some aspect of a device's performance.

PARAMETRIC EQ: An equaliser with separate controls for frequency, bandwidth and cut/boost. Found on most mixing desks and outboard equipment. The GML 8200 being a popular choice.

PASSIVE: A circuit with no active elements. 

PATCH BAY: A system of panel-mounted connectors used to bring inputs and outputs to a central point from where they can be routed using plug-in patch cords.

PATCH CORD: Short cable used with patch bays.

PEAK: Maximum instantaneous level of a signal.

PHASE: The timing difference between two electrical waveforms expressed in degrees where 360 degrees corresponds to a delay of exactly one cycle.

PHASER: Effect which combines a signal with a phase shifted version of itself to produce creative filtering effects. Most phasers are controlled by means of an LFO.

PEAK: The highest signal level in any section of programme material.

PFL: Pre Fade Listen; a system used within a mixing console to allow the operator to listen in on a selected signal, regardless of the position of the fader controlling that signal.

PPM: Peak Programme Meter; a meter designed to register signal peaks rather than the average level.

PHANTOM POWER: 48V DC supply for capacitor microphones, transmitted along the signal cores of a balanced mic cable.

PHASE: The timing difference between two electrical waveforms expressed in degrees where 360 degrees corresponds to a delay of exactly one cycle.

PHASER: Effect which combines a signal with a phase shifted version of itself to produce creative filtering effects. Most phasers are controlled by means of an LFO.

PHONO PLUG: Hi-Fi connector developed by RCA and used extensively on semi-pro, unbalanced recording equipment.
PITCH: Musical interpretation of an audio frequency.

PITCH BEND: A special control message specifically designed to produce a change in pitch in response to the movement of a pitch bend wheel or lever. Pitch bend data can be recorded and edited, just like any other MIDI controller data, even though it isn't part of the Controller message group.

PITCH SHIFTER: Device for changing the pitch of an audio signal without changing it's duration.

PLUG-IN: Software used in 

POLYPHONY: The ability of an instrument to play two or more notes simultaneously. An instrument which can only play one note at a time is described as monophonic.

POLY MODE: The most common MIDI mode that allows and instrument to respond to multiple simultaneous notes transmitted on a single MIDI channel.

PORT: Connection for the input or output of data.

POST PRODUCTION: Work done to a stereo recording after mixing is complete.

POWER SUPPLY: A unit designed to convert mains electricity to the voltages necessary to power an electronic circuit or device.

POST-FADE: Aux signal taken from after the channel fader so that the aux send level follows any channel fader changes. Normally used for feeding effects devices.

PRE-EMPHASIS: A system for applying high frequency boost to a sound before processing so as to reduce the effect of noise. A corresponding de-emphasis process is required on playback so as to restore the original signal, and to attenuate any high frequency noise contributed by the recording process.

PRE-FADE: Aux signal taken from before the channel fader so that the channel fader has no effect on the aux send level. Normally used for creating Foldback or Cue mixes.

PRESET: Effects unit or synth patch that cannot be altered by the user. 

PRINT THROUGH: The unwanted low level transfer of magnetic fields from one layer of analogue tape to another on the tape reel.

PROCESSOR: Device designed to treat an audio signal by changing its dynamics or frequency content. Examples of processors include compressors, gates and equalisers.  

PULSE WAVE: Similar to a square wave but non-symmetrical. Pulse waves sound brighter and thinner than square waves, making them useful in the synthesis of reed instruments. The timbre changes according to the mark/space ratio of the waveform.

PULSE WIDTH MODULATION: A means of modulating the duty cycle (mark/space ratio) of a pulse wave. This changes the timbre of the basic tone; LFO modulation of pulse width can be used to produce a pseudo-chorus effect.

PUNCH IN: The action of placing an already recorded track into record at the correct time during playback, so that the existing material may be extended or replaced.  

PUNCH OUT: The action of switching a tape machine (or other recording device), out of record after executing a punch-in. With most multitrack machines, both punching in and punching out can be accomplished without stopping the tape.

PQ CODING: Process for adding Pause, Cue and other subcode information to a digital master tape in preparation for CD manufacture.

PZM: Pressure Zone Microphone. A type of boundary microphone. Designed to reject out-of-phase sounds reflected from surfaces within the recording environment. 



Q: A measure of the resonant properties of a filter. The higher the Q, the more resonant the filter and the narrower the range of frequencies that are allowed to pass. 

QUANTIZE: A means of moving notes recorded in a MIDI sequencer so that they line up with user defined subdivisions of a musical bar, for example, 16s.