OAR – Original Aspect Ratio. The aspect ratio in which a movie was originally produced. Because the aspect ratio is sometimes changed to accommodate television screens and other formats, the OAR is used to indicates the original format.
object-based audio (OBA) – a method of producing surround sound in which sounds are directed toward a particular point in space, rather than a particular speaker or set of speakers. Originally designed for video games, object-based audio is now being used for immersive sound, so that sounds are directed according to the setup of a particular theater rather than a specific setup or a set number of speakers. Sometimes called object-oriented audio.
oblique mode – one of the three room modes in which resonance in a room is caused by sound reflecting off all six surfaces (four walls, floor, and ceiling) in a room.
oboe – a musical instrument in the woodwind family with a double reed and slender conical bore tube made of wood with holes that are opened and closed with keys and a slightly flared bell. It is a little smaller than a clarinet.
OCA Alliance – a trade organization founded in 2011 to promote the standardization and adoption of Open Communications Architecture through marketing, education, and training. It also develops new OCA standards and related materials to increase the value and usability of OCA as an interoperability tool for the media systems industry. In 2016, OCA was established as a standard by the AES.
occlusion effect – the phenomenon caused by wearing solid earplugs, hearing aids, or some in-ear monitors that causes a person's voice to sound hollow, boomy, and louder to themselves, the “voice-in-a-barrel” effect. A person can experience the effect by sticking their fingers in their ears and speaking.
octal tube – a vacuum tube that has an 8-pin base, developed by RCA in 1935.
octave – the interval between any two frequencies when the upper frequency is twice that of the lower frequency. For example, A5 has a frequency of 880 Hz, which is twice that of A4 at 440 Hz. The octave represents eight notes on the diatonic scale or twelve semitones. It is also called a perfect octave.
octave band – (1) All the frequencies within an octave. For example, there is one octave between 100 Hz and 200 Hz, as well as between 5 kHz and 10 kHz. (2) In acoustics, the range of frequencies in which the upper frequency limit is twice that of the lower frequency limit. For example, the octave band with a center frequency of 1000 Hz contains all frequencies from 707 to 1414 Hz. The lower limit can be calculated by dividing the center frequency by 1.4142 (the square root of 2), while the upper limit is the center frequency times 1.4142. Sound pressure level for a given space is often measured in octave bands, and the ISO has divided the audio spectrum into 10 equal parts, defining preferred center frequencies and upper and lower frequency limits as shown in the table below for bands 1 through 10. See also one-third octave band and one-half octave band.
odd-order harmonic distortion – harmonic distortion created when a waveform is distorted symmetrically, such as with digital clipping. Asymmetric distortion has more even-order harmonics, which reinforce the fundamental (original note). Human ears like the sound of even-order harmonics which is why some people prefer the sound of tubes over solid state electronics. Odd-order harmonics work against the fundamental and produce sounds that are not pleasing to the ear.
OEO – One End Open. Grounding one end (usually the sending end) of a connecting cable.
offload – to transfer the processing of a plug-in from the main microprocessor (CPU) to another microprocessor, such as a DSP accelerator. Dividing processing duties among multiple processors saves the processing power of the CPU.
ohm (Ω) – the unit for measuring resistance, defined as the electrical resistance between two points of a conductor when a constant potential difference of 1 volt is applied to these points to produce a current of 1 ampere. Named for German physicist Georg Simon Ohm, who was known for his discoveries in mathematics, acoustics, and electricity.
Ohm's law – the principle stating that the direct current flowing in a conductor is directly proportional to the potential difference between its ends, with the proportionality constant being the resistance of the conductor. It is usually stated with the formula V = IR, where V is the potential difference (voltage), I is the current in amperes, and R is the resistance, in ohms, of the conductor.
one-half octave band – (1) All the frequencies within one-half of an octave. (2) In acoustics, the range of frequencies in which the lower frequency limit is 1.4142 (square root of 2) times the lower frequency limit. The lower limit can be calculated by dividing the center frequency by 1.1892 (the fourth root of 2), while the upper limit is the center frequency times 1.1892. Sound pressure level for a given space is often measured in octave bands or one-third octave band, but sometimes half-octave bands are used. The center frequencies and upper and lower frequency limits for one-half octaves are shown in the table below. See also octave band and one-third octave band.
one-third octave – (1) Frequencies that are spaced every one-third of an octave apart, such as from C to E or A to C♯. One-third of an octave is 1.26-times above a starting frequency (1/3-octave = 21/3 = 1.260). Should not be confused with third octave. (2) The bandwidth of filters and equalizers that are 1/3-octave wide at the point of half-power (-3 dB). See one-third octave band.
one-third octave band – (1) All the frequencies within one-third of an octave. (2) In acoustics, the range of frequencies in which the upper frequency limit is 1.260 (cube root of 2) times the lower frequency limit. The lower limit can be calculated by dividing the center frequency by 1.1225 (the sixth root of 2), while the upper limit is the center frequency times 1.1225. Sound pressure level for a given space is often measured in octave bands or one-third octave band. The ISO and ANSI have established preferred center frequencies for one-third octaves, as shown in the table below. See also octave band and and one-half octave band.
online video distributor (OVD) – an over-the-top provider defined by the FCC as “any entity that offers video content by means of the Internet or other Internet Protocol (IP)-based transmission path provided by a person or entity other than the OVD.”
on-location – filming a movie or recording a television play or program at a place away from the studio.
open-back cabinet – a type of speaker cabinet in which the rear of cabinet is open or partially open, which means the sound can emerge from both the front and the back. This provides a broader dispersion, but generally produces less bass. Although open-back cabinets are most commonly used for electricguitar amplifiers (combo amps), they are occasionally used for other applications.
open-back headphones – a type of circumauralheadphones that has the back of the earcups open. While this configuration lets more ambient sounds into the headphone than closed-back headphones, it also leaks more sound out. However, such headphones provide a more natural and spacious sound. Also called open headphones or open-air headphones.
open circuit – a break in an electric circuit that prevents current from flowing. An open circuit can be either intentional, such as a switch, or unintentional, such as a broken wire.
Open Music Initiative (OMI) – a non-profit group of academic institutions, music and media organizations, creators, technologists, and policy experts whose mission is to promote and advance the development of open source standards and innovation related to music that help assure proper compensation for all creators, performers, and rights holders of music. Their goal is use new technologies to simplify the way music rights owners are identified and compensated so that sustainable business models for artists, entrepreneurs, and music businesses are created.
open sound control (OSC) – a method for communicating among computers, synthesizers, and other multimedia devices using networks. OSC sends control messages over a network using various data types commonly used in computers, whereas MIDI uses a cable and transmits only integers.
open tuning – a type of alternate tuning for string instruments, most commonly the guitar, in which strumming with no strings fingered or fretted creates a major or minor chord, rather than using standard tuning (EADGBE). Open tunings are quite often used when playing slide guitar, because you can you can change chords simply by placing a finger or slide across all six strings and moving to the desired fret. Two of the most popular open tunings are open G (DGDGBD) and open D (DADF♯AD).
opera – an extended dramatic work, in which all parts are sung to instrumental accompaniment, that usually includes arias, choruses, and recitatives, and that occasionally includes ballet.
operating frequency – (1) The rate at which a computer performs its basic operations. Also called a clock rate. (2) The main frequency used by a device, such as a transmitter, wireless microphone, or oscillator to perform its designed functions.
operating system (OS) – the software that manages and controls computerhardware functions, such as input and output and memory allocation, and that provides common services for computer programs, acting as an intermediary between the programs and the computer hardware. Application programs usually require a specific operating system in order to function. Examples of operating systems include Microsoft Windows, Apple OS X, Android, iOS, Linux, and UNIX.
operational amplifier – a circuit to amplifyvoltages often found in audio devices. The name comes from the fact that they were originally developed to carry out mathematical operations in analog computers. Today they are largely available as integrated circuits. Called op amp or opamp for short.
OPT – Open Plug-In Technology. A MIDI application plug-in format created by Yamaha. It is used in Sony ACID PRO 4, Yamaha SOL 2, and SONAR.
optical compressor – a compressor that uses a light source (usually an LED or electroluminescent panel) and a photoresistor to create changes in signal gain. Optical compressors tends to produce a smoother sound than conventional compressors because the response times of the light and the resistor soften the attack and release. Also called an opto-compressor.
optical disc recording modes – there are 3 main methods of recording recordable optical discs, such as CD-Rs or CD-RWs: disc-at-once (DAO), track-at-once (TAO), and session-at-once (SAO). DAO records the disc contents in one pass. In the TAO mode, the recording stops after each track, writing blocks and links to indicate the starting point for the next track. TAO discs can contain both data and audio on the same disc. SAO recording allows two or more sessions to be recorded and finalized on a single disc. Such sessions can be read from a hard disc by a computer, but more than one session usually is not readable by CD audio players.
optical fiber – a thin glass fiber through which light can be transmitted. Used with fiber optics.
optical printer – a device consisting of one or more movie projectors attached to a movie camera, that provides the ability to re-photograph portions of film to create special effects and/or to copy and restore old films.
optical sound – the type of sound reproduction on film that employs a photographic printing process of the optical track, as opposed to a magnetic stripe on the film.
optical soundtrack – the soundtrack on moviefilm in which a strip along the edge of the film containing audio waveforms that is photographically printed on the film through which light is shined and is converted to audible sound, a method called variable area. This was the primary means of providing sound on film until the advent of digital sound. Also called optical recording or optical track for short.
optical tremolo – a method often used in guitar amps to create tremolo. It features a circuit that uses a opto-isolator (optocoupler) to modulate the amplitude of the signal within the preamp stage of the amplifier. Such circuits often produce a lopsided wave, rather than a steady sine wave, which is quite pleasing on the ear. It is one of the distinctive characteristics of this type of tremolo. Also called optocoupled tremolo or photocell tremolo or opto for short.
optimized cardioid triangle (OCT) Surround – a method of recording surround sound developed by Dr. Gunther Theile. This approach uses directional microphones set apart at distances of up to 1 meter. It produces good separation in the front, good localization, and a large listening area with a natural-sounding effect.
optoelectronics – the study or use of devices in which an optical input produces an electrical output, or in which electrical stimulation produces a visible or infrared output. It should not be confused with electro-optics.
Opus – a lossyaudio coding format developed by the Internet Engineering Task Force (IETF) designed for interactive real-time applications over the internet. It is an open format that uses an audio codec called opus-tools. Use of Opus is under a royalty-free license.
Oracle Corporation – a multinational computer technology corporation founded in 1977 and headquartered in Redwood City, California. The develops and markets computer hardware and software, specializing in database management systems.
Orange Book – the informal name for the standard for the recordable compact disc (CD) developed by Philips and Sony and published in 1990, the a follow-up to the Red Book. The Orange Book is divided into two sections: Part I covers magneto-optical (MO) drives, and Part II covers the CD-R. Part III, released separately, deals with the CD-RW.
orchestra – a large ensemble of instruments with sections of strings, brass, woodwinds, and percussion instruments, typically having 60 to 100 musicians. A smaller-sized orchestra with fifty musicians or less is called a chamber orchestra. A full-size orchestra is sometimes called a symphony orchestra or philharmonic orchestra. These names do not indicate any difference in the purpose or constituency of the orchestra, but they are sometimes used to distinguish between two orchestral organizations located in the same city, such as the New York Philharmonica Orchestra or the New York Symphony Orchestra.
organ – a large musical instrument that makes sound by passing pressurized air through rows of tuned pipes and played by using one or more keyboards (called manuals) to produce a wide range of musical tones and effects. The pipes are grouped in sets called ranks with each rank having a common timbre and volume that the player can choose individually or in combinations through the use of controls called stops. Because pipe organs are very large and expensive, alternatives have been developed over the years. One option was replacing the pipes with reeds to create the reed organ, sometimes called a pump organ or harmonium. Later electronic organs were developed that used various electronic means to emulate pipe organ sounds, which were reproduced using a loudspeaker. Eventually, the electronic organ was combined with the synthesizer to create a electronic keyboard. Today a keyboard player can make the instrument sound like a piano, an organ, chimes, and many other sounds.
organist – a musician who plays a organ, especially one who performs expertly or professionally. See also keyboardist.
ORTF – Office de Radiodiffusion-Television Francaise. (1) The French national broadcasting system. (2) A standard established by ORTF for a stereo microphone technique that specifies two cardioid microphones spaced 17 cm (6.7 inches) apart and at an angle of 110 degrees. The ORTF technique produces recordings with a more open and spacious sound than those produced by the X-Y miking technique. ORTF works well when played back with headphone, but tends to have a somewhat dry sound lacking in warmth because it picks up minimal room ambience. However, it provides good mono compatibility, which is desired by the broadcasting industry. It falls into the near-coincident pair category of techniques. Other techniques in this category include A-B, DIN, EBS, Faulkner array, NOS, RAI. See also coincident pair (Blumlein array, mid-side, X-Y pair) and spaced pair (A-B, Decca tree, spaced cardioids, spaced omnis). See table comparing various stereo microphone techniques.
oscillation – (1) Movement back and forth at regular intervals. (2) Regular variation in amplitude, current, position, or other variable around a central point, such as produced by an oscillator.
oscillator – (1) A device or circuit a circuit that produces a regular alternating output of current, voltage, or sound at a specific frequency as determined by the characteristics of the circuit components. (2) A tone generator.
oscilloscope – an electronic instrument that displays an instantaneous trace of a waveform on a CRT screen.
OTL – Output TransformerLess. A type of output (from a microphone or amplifier) using a solid-statecircuit that requires no transformer. Historically, vacuum tubepower amplifiers had output transformers to isolate the high output impedance of the tubes and the low impedance of the speaker load.
ottava – musical notation indicating that a section of music is to be played an octave higher or lower than written. All' ottava alta (alternatively ottava sopra) means to transpose music up one octave, abbreviated as 8va. All' ottava bassa (alternatively ottava sotta) means to transpose music down one octave, abbreviated as 8vb. The abbreviation is shown above or below the staff with a dotted or dashed line ending with a vertical that indicates the notes to which it applies. Other abbreviations include 8a, 8a alta, and 8va bassa.
out of sync – two devices or music tracks that are not exactly aligned in time with one another. Opposite of in sync. See synchronize.
out-of-the-box (OTB) – a slang term referring to audio production in which all mixing and effects processing takes place primarily with hardware and equipment outside of the computer. Opposite of in-the-box.
out of tune – not being tuned to the same reference pitch, or all instruments in a group not being tuned alike. Opposite of in tune.
output – (1) The connector from which a device sends a signal or feeds another device. (2) The signal that a device sends out. (3) The amount of current, voltage, or power that a device delivers, such as 100-watt output of a power amplifier or a 12-volt power supply.
oven-controlled crystal oscillator (OCXO) – an oscillator operated inside a temperature-controlled space that maintains the crystal and the oscillator circuit at a constant temperature in order to increase stability and avoid drift due to temperature changes.
over – the condition in which the voltage of a signal presented to an A/D converter exceeds 0 dbFS. An over is an indication of digital clipping. While a brief excursions beyond 0 dBFS cannot be heard, there is no agreement as to how far above 0 dbFS and for how long an excursion must be before an over is audible.
overhang – the continuation of a signaloutput after its input has stopped. Sometimes called ringing.
overhead microphones – (1) One or two microphones placed over a source, such as over a drum kit to capture the sound of the cymbals and overall sound of the kit. (2) Microphones hung from the ceiling, such as for miking choirs or theater stages. Called overheads for short.
overload – (1) To exceed the maximum inputlevel of a system causing distortion (analog) or clipping (digital). (2) To drive a signal into distortion, an effect sometimes used with electric guitars and other instruments. Also called overdrive.
overtone – any of a series of musical tones whose frequencies may or may not be integral multiples of the fundamental frequency, but usually are. A harmonic is always an exact multiple. However, they are numbered differently with the fundamental being the first harmonic, but the first overtone is equivalent to the second harmonic. See also partial.
oxygen-free copper (OFC) – copper that has been electrolytically refined to reduces the level of oxygen it contains. While oxygen-free copper improves electrical conductivity, the amount of improvement is insignificant in audio applications.
Note: We believe this is the largest dictionary (glossary) of terms specific to usage within the recording industry that is currently available on the internet, with more than 8,000 entries, nearly 600 illustrations, and dozens of tables. Some of the terms have different or additional meanings in other situations, especially within the electronic, automotive, scientific, and computer industries. Of necessity there are obvious overlaps into other fields such as music, electronics, and computers, but such excursions are limited to information deemed pertinent to the knowledge required to operate and/or participate effectively in the workings of a recording studio. Also included are terms related to sound reinforcement (live performances) including wireless microphone technology because a working knowledge of that terminology is necessary for recording at live performance venues. Because recording studios also record audio for video and motion pictures (films), some terminology from those fields is included. Some scientific terms are included because they help explain studio terminology. For example, electromagnetism explains how microphones, loudspeakers, and guitar pickups work. Knowledge of radio waves and the radio frequency spectrum is needed to explain wireless devices. Any trademarks or trade names mentioned belong to their respective owners. The information contained in this dictionary is believed to be accurate at the time of publication. This information is subject to change without notice. The information was obtained from and cross-checked with a variety of sources that are believed to be reliable. However, Los Senderos Studio, LLC does not guarantee the accuracy or completeness of the information contained herein. Please contact us to report any errors, omissions, discrepancies, or broken links. Los Senderos Studio shall not be responsible for any consequences or damages arising out of the use of this information. Nothing in this glossary should be interpreted as legal advice. For a glossary providing information on legal and business matters for musicians, we suggest you consult Musicians Business Dictionary.
A note on alphabetical order: The terms in this glossary are alphabetical without regard to spaces and punctuation. For example, AM Radio follows amplitude. While this may seem to be at odds with other conventions, it eliminates confusion with words such as pickup, which is sometimes written as pick up or pick-up. The entries on the number page (0-9) are listed in increasing value within each digit. For example, all of the entries beginning with 1 are listed before those starting with 2. For Greek letters (α-ω), the entries are in Greek alphabetical order.