Glossary of Audio, Recording
and Music Terms "O"
Octave – An interval or difference of pitch of 12 half-steps. In our standard tuning system, the higher note in an octave is exactly double the frequency of the lower note.
Off Axis — Veering away from the imaginary line (axis) directly in front of the receiving end of a microphone. Measured as degrees of an angle. (For example, a sound coming from directly behind the microphone is said to be 180 degrees off-axis.)
Offset Time – 1) The SMPTE time that will trigger a MIDI sequencer to begin. 2) The amount of position difference needed to get two reels to play the music in time.
Ohm (W) – The unit used to measure the amount of opposition (impedance) to electrical current flow in a signal or device. (See also “Impedance.”)
Ohm’s Law – The mathematical relationship between voltage, current and resistance.
Omni – A prefix meaning “all.”
Omnidirectional Pattern – In microphones, picking up evenly from all directions (sometimes also called “Nondirectional”). 2) In speakers, sending out the signal evenly in all directions.
Omni Mode – A setting that enables a MIDI device to recognize and respond to all MIDI channels at once.
On Axis – The position directly in front of the diaphragm of a microphone, in line with its movement.
Op Amp – See “Operational Amplifier.”
Open Circuit – An electrical circuit that is disconnected, interrupted or incomplete, preventing the flow of electricity.
Operating Level – (Sometimes called “Reference Level“) The maximum level that should not be exceeded in normal operation.
Operational Amplifier – (Abbreviated “Op Amp“) An amplifying circuit used in most audio and electronic devices.
Oscillator – 1) A tone generator in a synthesizer. 2) A device that puts out test tones at various frequencies.
Out Of Phase – 1) Being similar to another signal in amplitude, frequency and wave shape but being offset in time by part of a cycle. 2) Having the opposite polarity.
Outboard Equipment – Equipment that is used with, but is not a part of, a console.
Output – 1) The jack or physical location of where a device sends out a signal. 2) The signal put out by a device.
Output Impedance – The opposition to the flow of electrical current by the output circuits of an amplifier (or other device).
Output Level – The signal level at the output of a device.
Overdubbing – The process of recording an additional musical performance over an existing recording, usually on its own track. Overdubbing has become a common recording technique with the advent of multitrack recording, first on multitrack analog tape, and more recently via computers and Digital Audio Workstations (DAWs).
Overtone – Any harmonic in a tone except the fundamental frequency. (See also “Partial.”)