Pro Audio Reference


Pro Audio Reference (O)


1/4" TRS or 1/4" TS See connectors.

100Base-T or 1000Base-T See Ethernet.

1/f noise See flicker noise.

OAG (old analog guy) As opposed to a YDG.

obbligato Music Terminology. "'Necessary': term used for an independent and essential part in concerted music, secondary to the principal melody." [Sadie]

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

obstacle gain The ratio, usually expressed in dB, of the electromagnetic field at a point in the vicinity of the geometrical shadow of an obstacle to the field which would occur in the absence of the obstacle. [IEEE]

OCA (Open Control Architecture) An alliance of pro audio manufacturers with the goal of creating an open public communications standard for control and monitoring of devices in professional media networks.

ocarina Musical Instrument. A small terra-cotta or plastic wind instrument with finger holes, a mouthpiece, and an elongated ovoid shape. Named after Italian oca, goose, from the fact that its mouthpiece is shaped like a goose's beak. [AHD] Made famous when Bob Hope, Bing Crosby and Dorothy Lamour played ocarinas and sang the song, When the Sweet Potato Piper Plays in the movie Road to Singapore, in 1940. [Thanks GS!] And who can forget the ocarina solo in the soundtrack of The Good, The Bad, and the Ugly in 1967. See Ocarina History; also Viennese Vegetable Orchestra.

Occam's razor A rule in science and philosophy stating that entities should not be multiplied needlessly. This rule is interpreted to mean that the simplest of two or more competing theories is preferable and that an explanation for unknown phenomena should first be attempted in terms of what is already known. Also called law of parsimony. [After William of Ockham.] [AHD]

occluded ear simulator Ear simulator that simulates the inner part of the ear canal, from the tip of an ear insert to the eardrum. [IEEE]

occlusion or occlusion effect Hearing. 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. The earplugs block the ear canal resulting in a sound similar to sticking a finger in each ear and talking. This closure effect also produces louder sounds to the wearer since the ear canal blockage allows additional sound pressure to build up (rather than escape out the open ear canal) and be conducted to the inner ear. This is easily demonstrated by pronouncing and sustaining the word "fee," then sticking your fingers in your ears and notice how much louder it sounds (oh go ahead, no one is looking).

octal A number system using the base-8, i.e., each digit can be any of 8 values, represented by the digits 0-7. A three-bit binary number (since 23 = 8) can also represent each octal digit.

octant Acoustical Geometry. One of the eight equal regions into which a set of three orthogonal planes divides three-dimensional space. An example of an octant is the region (x > 0, y > 0, z > 0), where x, y, z are rectangular coordinates. [Morfey]

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

octave 1. Audio. The interval between any two frequencies having a ratio of 2 to 1. 2. Music 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 Music. 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] Computers. Eight bits, also called a byte.

Octopus Recording. 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. A terrific website for unusual and bazaar music-making creations.

OEM (original equipment manufacturer) The true manufacturer of equipment sold under another name.

OEO (one end open) Wiring. 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] Named after Hans Christian Oersted (1777-1851), Danish physicist. [AHD]

oeuvre 1. A work of art. 2. The sum of the lifework of an artist, writer, or composer. [AHD]

OFC (oxygen-free copper) Wire & Cables. Another of the popular audiophile myths that OFC power cables can improve sound. See Howard Johnson's wonderful essay titled: OFC madness: Facts, not fantasy, regarding power cables for high-end audio equipment.

O+ Festival Festival that began in Kingston, NY in 2010, and is now expanding to other venues like the one held in 2013 in San Francisco. This is a festival celebrating music and the arts.

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 The start or initial stage; the outset. [AHD] Within pro audio typical offset categories are level, time, phase, and wavelength.

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) Networks. 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 (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.] [Note: Georg Ohm did NOT formulate the basic power equations; that was done by James Joule: see Joule's Law.]

ohnosecond A very short moment in time during which you realize that you have pressed the wrong key and deleted hours, days, or weeks of work. []

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.

OITC (outdoor-indoor transmission class) Noise Measurement. A sound isolation measurement protocol, used to indicate the rate of sound transmission between outdoor and indoor spaces.

Okedo Daiko Muscial Instrument. Japanese two-headed percussion drum.

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 (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. See OLED for details.

OL light See overload light.

Olson, Harry Ferdinand, Ph.D. (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.

omele Musical Instrument. The base of the bata drums consisting of 3 or 4 small drums tied together.

omnidirectional microphone One with a response pattern that is as close to a perfect sphere as possible. Receives sound from all directions equally well. Compare with unidirectional mic and cardioid microphone.

on-axis response See off-axis response.

ondes Martenot Synthesizers. (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. It was the female voice effect in the original Star Trek TV theme.

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. See critical bands. Compare with third-octave.

one-third octave SPL The sound pressure level of the sound contained within a one-third octave frequency band.

onomastics 1. a. The study of the origins and forms of proper names. b. The study of the origins and forms of terms used in specialized fields. 2. The system that underlies the formation and use of proper names or terms used in specialized fields. [AHD]

onomatopoeia The formation or use of words such as buzz, hiss, splash, sizzle or murmur that imitate the sounds associated with the objects or actions they refer to. [AHD] See zaa zaa.

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

OOP See object-oriented.

opacity 1. The quality or state of a body that makes it impervious to the rays of light; broadly : the relative capacity of matter to obstruct the transmission of radiant energy. 2.An opaque spot in a normally transparent structure (as the lens of the eye) [MWD]

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. See vacuum-tube op amps.

open circuit Electronics. The condition where there is no connection between two nodes, resulting in zero current flow between the nodes. Electricity. Containing a gap across which electricity cannot pass: an open circuit.[AHD]

opera 1. A theatrical presentation in which a dramatic performance is set to music. [AHD] 2. "I do not mind what language an opera is sung in so long as it is a language I don't understand". Edward Appleton, Observer August 28, 1955. [Crystal] 3. "An unalterable and unquestioned law of the musical world required that the German text of French operas sung by Swedish artists should be translated into Italian for the clearer understanding of the English-speaking audiences". Edith Wharton, 1920, The Age of Innocence. [Crystal]

ophicleide Musical Instrument. A family of keyed brass instruments.

optical-fiber cable See fiber-optics.

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) Musical Instrument. 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 Computer Science & Logic. 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.

orange One of the words in the English language without a rhyme — some others are "month," "purple," and "silver."

orange noise See noise color.

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

organ Music. 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 See OLED.

organ of Corti Hearing. 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]

organ trio A group of three musicians playing a Hammond organ, a drummer and a jazz guitarist.

oronyms Speech. Streams of sound than can be carved into words in two different ways, i.e., it illustrates the seamlessness of speech. For example oronyms are often found in songs and nursery rhymes such as the famous "Mairzey doats and dozey doats, And little lamsey divey, A kiddley-divey do, Wouldn't you?" From Pinker.

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. Mathematics. 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 Electronics & Synthesizers. A circuit that continuously alternates between two (or more) states [IEEE]; the period between alternations defines the frequency of oscillation. A common said complaint of electronic engineering students is that they build "amplifiers that oscillate and oscillators that amplify".

oscilloscope Electronic Test Equipment. 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 (optimal source distribution) Localization. A system to eliminate or improve the degradation caused by cross-talk cancellation techniques used in binaural sound reproduction.

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

OSHA U.S. Occupational Safety and Health Administration

Osheaga A music and arts festival held on Montreal's Saint Helen's Island, is considered one of the most important festivals of its genre in Canada. Known as The Festival de la Musique et des Arts to Montreal natives..

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 See The 7 Layers of the OSI Model.

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

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

otacoustic Hearing. Any external apparatus that improves hearing, e.g., an ear trumpet.

OTL (output transformerless) Power Amplifiers. 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."

otoacoustic emission Hearing. Sound generated from the inner ear and observable as sound in the external ear canal.

otolaryngology Hearing. The branch of science that treats diseases of the ear, nose and throat.

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 (aka ud) Musical Instrument. 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.

Outer Banks Bluegrass Island Festival See: Bluegrass Island Festival.

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

output impedance Electronics. 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.

Outside Lands Three-day festival held in Golden Gate Park, San Francisco since 2009 featuring music, food, wine, beer and art.

oval window Hearing. "A tiny membranous window on the cochlea to which the foot plate of the stirrup ossicle is attached. The sound from the eardrum is transmitted to the fluid of the inner ear through the oval window." [Everest]

ovcharska svirka Musical Instrument. Bulgarian shepherd's pipe.

overdrive box See: effects boxes.

overdub Recording. 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.

override Signal Processing. See: ducker.

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. See the RaneNote Digital Dharma of Audio A/D Converters.

overtone Any frequency higher than the fundamental frequency of a sound. See: harmonic.

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

oxide, magnetic Recording. 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]

Oz From Frank Baum's "The Wizard of Oz," the name was created when he looked at his filing cabinet and saw "A-N," and "O-Z," hence "Oz."

AES - Audio Engineering Society