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Dictionary of Audio Terminology - O


object-oriented or object-based programming - (Abbreviated OOP) A software technique in which a system program is expressed completely in terms of predefined things (objects), consisting of a set of variables and operations which can be performed on them, and the connections between objects.

oblique mode - Sound reflecting between all six sides of a rectanguloid. Compare with tangential mode and axial mode.

ocarina - A small terra-cotta or plastic wind instrument with finger holes, a mouthpiece, and an elongated ovoid shape.

occlusion or occlusion effect - The phenomenon resulting from wearing solid earplugs, hearing aids or some personal monitors that makes the wearer's voice sound hollow and boomy to themselves, i.e., a voice-in-a-barrel effect.

octal - A number system using the base-8.

octant - One of the eight equal regions into which a set of three orthogonal planes divides three-dimensional space.

octaphonic or octophonic - Systems using eight discrete channels for recording and playback.

octave – (1) The interval between any two frequencies having a ratio of 2 to 1. (2) a. The interval of eight diatonic degrees between two tones, one of which has twice as many vibrations per second as the other. b. A tone that is eight full tones above or below another given tone. c. An organ stop that produces tones an octave above those usually produced by the keys played. [AHD]

octet - a. The interval of eight diatonic degrees between two tones of the same name, the higher of which has twice as many vibrations per second as the lower. b. A tone that is eight diatonic degrees above or below another given tone. c. Two tones eight diatonic degrees apart that are sounded together. d. The consonance that results when two tones eight diatonic degrees apart are sounded. e. A series of tones included within this interval or the keys of an instrument that produce such a series. f. An organ stop that produces tones an octave above those usually produced by the keys played. g. The interval between any two frequencies having a ratio of 2 to 1. h. A music group consisting of eight members & instruments. [AHD] In reference to computers, eight bits, are called a byte.


Octopus - The name given by comedian W.C. Fields for Les Paul's original Ampex 8-track Sel-Sync™ recorder.

octothorpe - The "#" symbol on the telephone keypad, also known as a pound sign, crosshatch, number sign, sharp, hash, crunch, mesh, hex, flash, grid, pig-pen, gate, hak, oof, rake, fence, gate, grid, gridlet, square, and widget mark. Click the link to read the history of this creative word.

OEO (one end open) - Abbreviation used as shorthand when discussion the practice of only grounding one end (the sending end) of a connecting cable.

oersted - Abbr. Oe The unit of magnetic field strength (intensity) in the centimeter-gram-second electromagnetic system, equal to the magnetic intensity one centimeter from a unit magnetic pole. [IEEE]

OFC (oxygen-free copper) - Another of the popular audiophile myths that OFC power cables can improve sound.

off-axis response - Any direction other than the on-axis response, i.e., the response measured along the imaginary straight line drawn through the geometric center of an object. In pro audio most often used in measurements of loudspeakers, microphones and humans.

offset binary - A digital coding scheme for bipolar signals that represents the most negative value with all zeros and the most positive value with all ones.

Ogg Vorbis - An open, royalty-free, pro audio encoding and streaming technology that competes with AAC, TwinVQ and other schemes. The name "Ogg" comes from a video game and "Vorbis" from a Terry Pratchett novel.

OHCI (Open Host Controller Interface) - Based on the IEEE-1394 specification, however, it goes beyond the basic specs. It allows for hard drives, CDR’s, scanners, audio and video devices, digital still cameras, mixers, and more to be controlled.

ohm - Abbr. R or Greek upper-case omega, Ω - A unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt across its terminals. [After Georg Simon Ohm.]

Ohm, Georg Simon - (b. 1789-1854) German physicist noted for his contributions to mathematics, acoustics, and the measurement of electrical resistance. [AHD]

ohmage - Archaic British term for loudspeaker resistance. No longer used; replaced by the term impedance.

Ohm's Acoustic Law - The law stating that a complex musical sound is heard as the sum of a number of distinct pure tones which can be resolved by Fourier analysis [OED]. [After Georg Simon Ohm.]

Ohm's Electrical Law - The law stating that the direct current flowing in a conductor is directly proportional to the potential difference between its ends. It is usually formulated as V = IR, where V is the potential difference, or voltage, I is the current, and R is the resistance of the conductor. [After Georg Simon Ohm.]

OIART (Ontario Institute of Audio Recording Technology) - This Canadian school offers a three-term, forty-six week immersion course designed to prepare graduates for a career in the professional audio recording and audio communications industry.

oldest musical instrument - A 35,000-year-old flute found in Germany is believed to be the first musical instrument.

OLED (organic light emitting diode) - A type of LED display made from organic polymers that provides a wide viewing angle and uses low power.

OL light (overload light) - An indicator found on pro audio signal processing units that lights once the signal level exceeds a preset point.

Olson, Harry Ferdinand, Ph.D. - (b. 1901-1982) American engineer who worked 40 years at RCA labs, recognized and honored as a pioneer and leading authority in acoustics and electronic sound recording. He was granted over 100 patents, along with many awards and medals for his contributions to the science of sound. He authored more than 130 technical papers and wrote several textbooks still considered the best of their genre.

omnidirectional microphone - One with a response pattern that is as close to a perfect sphere as possible. Receives sound from all directions equally well.

on-axis response - the response measured along the imaginary straight line drawn through the geometric center of an object. In pro audio most often used in measurements of loudspeakers, microphones and humans.

ondes Martenot - pronounced (oenz MAR-te-noe) An early synthesizer from 1928. A monophonic theremin-sounding instrument using a stretched wire under a keyboard with timbre and loudness controls.

one-bit data converter - Loose reference to any of the various data conversion schemes (e.g., delta-sigma, adaptive delta modulation, etc.) that use only one binary bit (i.e., levels 1 and 0) in the conversion and storage process.

one-third octave – (1) Term referring to frequencies spaced every one-third of an octave apart. One-third of an octave represents a frequency 1.26-times above a reference, or 0.794-times below the same reference. The math goes like this: 1/3-octave = 21/3 = 1.260; and the reciprocal, 1/1.260 = 0.794. Therefore, for example, a frequency 1/3-octave above a 1 kHz reference equals 1.26 kHz (which is rounded-off to the ANSI-ISO preferred frequency of "1.25 kHz" for equalizers and analyzers), while a frequency 1/3-octave below 1 kHz equals 794 Hz (labeled "800 Hz"). Mathematically it is significant to note that, to a very close degree, 21/3 equals 101/10 (1.2599 vs. 1.2589). This bit of natural niceness allows the same frequency divisions to be used to divide and mark an octave into one-thirds and a decade into one-tenths. (2) Term used to express the bandwidth of equalizers and other filters that are 1/3-octave wide at their -3 dB (half-power) points. (3) Approximates the smallest region (bandwidth) humans reliably detect change.

oompah - A rhythmic sound made by a tuba or other brass instrument. [AHD]

OOP - A software technique in which a system program is expressed completely in terms of predefined things (objects), consisting of a set of variables and operations which can be performed on them, and the connections between objects.

op amp (operational amplifier) - An analog integrated circuit device characterized as having two opposite polarity inputs and one output, used as the basic building block in analog signal processing.

open circuit - The condition where there is no connection between two nodes, resulting in zero current flow between the nodes. Containing a gap across which electricity cannot pass.

optical-fiber cable - The technology of using glass fibers to convey light and modulated information. Short distances (typically less than 150 feet) use plastic fibers, while long distances must use glass fibers.

optical microphone - Many designs exist but it seems like Sennheiser's new design (based on a licensing arrangement with the Israeli company Phone-Or (owner of US Patent 5,771,091) is the best yet. See: Sennheiser MO 2000. Here's how it works (paraphrased from the data sheet): light from an LED is directed onto a reflective diaphragm via an fiber optic cable. The diaphragm reflects part of the light into a receiver fiber optic cable. If the diaphragm is moved by sound signals, the reflected light bean is deflected, with the result that more or less light is coupled into the receiver fiber optic cable. At the end of the receiver fiber optic cable, a photodiode converts the light intensity variations into electric signals. The results are impressive: an omnidirectional polar pattern with 20 Hz to 40 kHz frequency response and a maximum 134 dB-SPL.

Optigan (Optical organ) - A portmanteau word naming a type of consumer electronic keyboard introduced in 1971 by a division of Mattel.

Optocoupler - Any device that functions as an electrical-to-optical or optical-to-electrical transducer.

Optophonic Piano - Invented by Vladimir Baranoff Rossine, a very early color organ.

OR - A Boolean logical operator that returns a true value if one or both operators are true; a form of addition. For example, two parallel connected switches, A and B, requires one or both be closed for current to pass, thus it requires switch A OR switch B closed to operate.

Ordinate - The plane Cartesian coordinate representing the distance from a specified point to the x-axis, measured parallel to the y-axis. [AHD]

Organ – (1) An instrument consisting of a number of pipes that sound tones when supplied with air and a keyboard that operates a mechanism controlling the flow of air to the pipes. Also called pipe organ. (2) Any one of various other instruments, such as the electronic organ, that resemble a pipe organ either in mechanism or sound. [AHD]

organic LED (organic light emitting diode) - A type of LED display made from organic polymers (think plastic that glows) that provides a wide viewing angle and uses low power. OLED displays do not require a backlight as do LCD screens. OLED screens can also be fabricated on plastic as well as glass substrates, making them more flexible and durable.

organ of Corti - A specialized structure located on the inner surface of the basilar membrane of the cochlea containing hair cells that transmit sound vibrations to the nerve fibers. [AHD]

oronyms - Streams of sound than can be carved into words in two different ways, i.e., it illustrates the seamlessness of speech.

orotund – (1) Pompous and bombastic: orotund talk. (2) Full in sound; sonorous: orotund tones. [AHD]

ORTF (Office de Radiodiffusion -- Television Francaise) - An initialism formed from the name of the French national broadcasting system, who designed a stereo microphone recording technique known as the ORTF method. The technique uses two cardioid microphones with a spacing of 17 cm between the microphone diaphragms, and with an 110° angle between the capsules. This technique reproduces stereo cues similar to those used by the human ear to perceive directional information in the horizontal plane. The spacing of the microphones emulates the distance between the human ears, and the angle between the two directional microphones emulates the shadow effect of the human head. The ORTF stereo technique provides the recording with a wider stereo image than X-Y stereo while still preserving good mono information.

orthogonal - (1) Relating to or composed of right angles. (2) a. Of or relating to a matrix whose transpose equals its inverse. b. Of or relating to a linear transformation that preserves the length of vectors. [AHD]

oscillator - A circuit that continuously alternates between two (or more) states [IEEE]; the period between alternations defines the frequency of oscillation.

oscilloscope - An instrument primarily for making visible the instantaneous value of one or more rapidly varying electrical quantities (typically voltage) as a function of time or another electrical or mechanical quantity. [IEEE]

OSD (on-screen display) chip - An integrated circuit providing all necessary functions for adding text to television or video monitor display screens.

OSI (open system interconnection) - The only internationally accepted framework of standards for communication between different systems made by different vendors. The model originally developed by ISO describing computer communication services and protocols without making assumptions concerning language, operating systems or application issues. The main goal is to create an open systems networking environment where any vendor's computer system, connected to any network, can freely share data with any other computer system on that network.

ossicles - The group of the three bones of the middle ear commonly known as the hammer, anvil and stirrup.

ostinato - A short melody or pattern that is constantly repeated, usually in the same part at the same pitch. [AHD]

OTL (output transformerless) - Historically vacuum tube power amplifiers had output transformers that isolated the high output impedance of the tubes and the low impedance of the loudspeaker load. Years later tube amplifiers evolved into cathode follower designs that no longer required output transformers, thus they became "output transformerless."

OTPROM (one-time programmable read-only memory) - A redundant term, incorrectly used to mean PROM -- a PROM, by definition, is a one-time device.

oud - A musical instrument of northern Africa and southwest Asia resembling a lute. [AHD]

outboard unit - External, usually referring to a separate piece of signal processing gear located remote to a mixer that connects in the effects loop.

out-of-phase - In an un-synchronized or un-correlated way. See polarity and phase et al.

output impedance - The output driving impedance of a device, usually low in the 50-300 ohm range. Output impedance is frequency dependent and varies as a function of circuit feedback, therefore the value given must state the frequency range it covers.

Overdub - To add (supplementary recorded sound) to a previously taped musical recording especially in order to heighten the total effect. Additional recorded sound that is blended into a musical recording. [AHD] Usually done while listening to the previously recorded music on the same tape recorder or device.

overload light or OL light - An indicator found on pro audio signal processing units that lights once the signal level exceeds a preset point. There is no standard specifying when an OL light should illuminate, although common practice makes it 3-4 dB below actual clipping. Good signal processing design ensures that the OL light illuminates anytime the signal exceeds the set point, anywhere in the signal path, not just the input or output level.

overs - A term associated with A/D converters used to describe input signals exceeding the full scale range (0 dBFS). Overs indicators vary from simple single LEDs to elaborate calibrated digital meters. To be of genuine value the overs indicator, however displayed, must be based on reading the true digital code associated with the input level. It is important to distinguish between 0 dBFS and overs; they are not the same. 0 dBFS is the absolute highest voltage level that any particular A/D can convert. It produces the equivalent of a digital code consisting of all 1s. No digital level can exceed 0 dBFS. A 0 dBFS voltage level and all levels greater than this produce the same output code of all 1s. A true overs indicator actually counts the number of times that the 0 dBFS level was exceeded and displays this number. As yet there is no standard as to how many samples exceeding 0 dBFS constitutes an over. Everyone agrees that very brief excursions beyond 0 dBFS (producing digital clipping) cannot be heard; however no such agreement exists as to just how many samples it takes before an over is audible.

oversampling – (1) Sampling at a rate higher than the sampling Nyquist theorem. (2) A technique where each sample from the data converter is sampled more than once, i.e., oversampled. This multiplication of samples permits digital filtering of the signal, thus reducing the need for sharp analog filters to control aliasing.

Overtone - Any frequency higher than the fundamental frequency of a sound.

OXCO (oven-controlled crystal oscillator) - Very stable form of crystal oscillator.

oxide, magnetic - Magnetically responsive material forming the basis of magnetic recording. It comes in a variety of types with different recording properties, especially suited to the needs of audio tape or videotape recording at a variety of densities of recording. [Holman]





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HistoryOfRecording.com acknowledges the Elsevier, Inc. publication, Audio Engineering know it all, the University of Washington Press publication, The Audio Dictionary, second edition, the Howard W. Sames & Co., Inc. publication, Audio cyclopedia, the Cambridge University Press publication, The Art of Electronics, Rane Corporation (Dennis A. Bohn, CTO), Houghton Mifflin Company publication, The American Heritage Dictionary of the English Language, Fourth Edition, the IEEE publication, IEEE 100: The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition and Wikipedia in the preparation of this Dictionary of Audio Terminology.

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