Audio-Visual Glossary

O

 

OBE: Abbreviation for Optical Bass Extension. This is a bass channel for low frequency sounds on film soundtracks utilised in the original Dolby Stereo surround sound format. It is called optical because the entire film soundtrack was on an optical track on the film itself.

 

OCEANWAY (STUDIOS): A large very famous studio in LA on Sunset Blvd, formerly owned by Allen Sides. He recently sold this complex of studios to a company named Cello. Allen still has Oceanway Studios in North Hollywood and in Nashville, Tennessee.

  

OCN: Stands for ORIGINAL CAMERA NEGATIVE. See ORIGINAL CAMERA NEGATIVE.

 

OCTAVE: A range of tones where the highest tone occurs at twice the frequency of the lowest tone. In the common musical scale, as played on a piano, every 8 notes starts and ends an octave.

 

OEM: 1) An abbreviation for Optical Experts Manufacturing. This is the company in Charlotte, North Carolina that makes the final masters for our c.d. production. These are the masters used in the c.d. replication plant for mass production of compact discs. 2) An electronics industry abbreviation for Original Equipment Manufacturer.

 

OFF-AIR HDTV TUNER: Many earlier model High Definition televisions were sold without an internal tuner with which to receive Digital TV High Definition broadcasts from local network television stations. The reason is that the methods and specifications for such a tuner had, at that time, not been worked out. For those consumers who have purchased such TVs without a tuner, a separate tuner can be purchased to update their HDTV sets.

       

OFF-AXIS: 1) Away from the front, off to the side of a speaker or not facing a microphone directly straight on. 2) Literally, any angle of deviation from a centre axis. 

 

OFF-LINE, OFF-LINE EDIT: The first stages of a video edit, done “off the main production line”. (The main production line is the editing facility where all the video pictures and special effects are combined into their final form.) The off-line edit is where the basic edit of the video is worked out and put together.  Once an off-line is approved, it then goes “on line” (to the main, final video editing line) where it is fully assembled using final footage, all SFX shots, etc.

 

OFF-LINE BAY: The word “bay” means any compartment or space which is sectioned off for its own purpose or function. It comes from the French word meaning “an opening in a wall”. The “Off-Line Bay” is the production line in Cine Editing where the first phase of editing is done for our video products. (See OFF-LINE EDIT.)

 

OFF-MIC: When a sound source is outside of the accurate pick-up area of a microphone.  

 

OFFSET: Said of sound when mixing different sound elements from different recording machines or when watching a mix against pictures and the sounds and-or pictures are not in synch together. There is misalignment - an “offset” - as regards time. The amount of offset can be precisely measured and corrected.

 

OFF THE BOARD: A recording or mix coming from the mix-board itself, as opposed to a tape or other type of copy. “We listened to the mix off the boards and it AB’d with the copy.”

 

OFF TO THE LEFT, OFF TO THE RIGHT:  1) The sound of the mix as heard over loudspeakers and/or headphones leans to the left or to the right volume-wise; it’s louder on one channel than the other. 2) A loudspeaker system can be misadjusted so that one channel is louder than the other causing the sound to appear “heavy on the left” or “heavy on the right”. This can even be caused by having the loudspeakers improperly aimed.

 

OHM: The measurement of resistance is an ohm, which is defined as the resistance d.c. current encounters in a small column of mercury, 1063mm long and weighing 14.451grams. The symbol for Ohm is the Greek letter “omega”. (See OHM, GEORG SIMON).

 

OHM, GEORG SIMON: (1789-1854) German physicist noted for his contributions to mathematics, acoustics, and the measurement of electrical resistance.

 

OHM’S LAW: A basic law and formula used to measure electrical current flow. Ohm’s Law states that the electrical current flow in a circuit is equal to the voltage divided by the resistance.  In order to make this into a math formula that could be used in conceiving and designing electrical circuits, these things were given symbols. The symbol for amperes of current is “I”. The symbol for voltage is “V”. And the symbol for Ohms of resistance is “R”. Therefore, the formula for Ohm’s Law is: I = V/R.

 

OMF: Abbreviation for Open Media Format. This is a type of computer operating system that allows files or plug-in cards from other types and brands of computers to be used in addition to those specifically manufactured for a given computer or computer system. It’s called an “Open Media Format” because it accepts and can work with files and plug-in accessories by other manufacturers.  OMF is specifically an Avid format and allows the Avid to be used with additional plug-in circuit boards and files from other computer manufacturers.

 

OMFI: An abbreviation for Open Media Format Interchange.  This is a proprietary format made for use in Avid computerised editing workstations. The basic type of file is “open media”, which means that the Avid is capable of accepting computer files made on workstations from other manufacturers. “Interchange” refers to the transfer of data between computers. Avid’s OMF files are stored in a folder called “OMFI”. This simply means that this folder contains files that are interchangeable between one format of computer and the Avid.

 

OMNI DIRECTIONAL MICROPHONE:        A microphone that picks up sound from all directions.  

         

ON-AXIS: 1) The position directly in front of the diaphragm of a microphone, in line with its best ability to pickup sound. 2) Also when within the accurate sound reproduction area of a loudspeaker, one is on-axis to that speaker.  

 

ONE BIT, ONE-BIT: Some brands c.d. players and other digital audio equipment has written on it the term, “One-Bit”. Digital audio recording and playback involves taking a “snapshot” thousands of times per second of the sound. This is called the “sampling rate”—it is how many “samples” are taken per second of the audio signal. For compact discs, this is done 44,100 times per second. Each one of these samples has a certain number of data bits assigned. Some of these bits are “on” and others are “off”. Therefore, for every second of audio program, there are 44,100 different amounts of “on” and “off” bits. It is this series of “on” or “off” amounts that is read by the c.d. player and converted into audible sound. CDs have 16 bits per sample. If the audio is very loud, there might be a full 16 bits assigned. If it is low in volume, there might be only 12 bits. A “One-Bit” c.d. player does things differently. Instead of having 16 bits with which to “view” each of the 44,100 samples every second, the One-Bit player takes millions of samples per second, yet it only assigns each sample just one bit—and that bit is either “on” or “off”. Because there are so many samples taken per second, the c.d. player needs to read only one bit for each sample. The player sees if that bit is “on” or “off”—and the millions of times it sees that “on or off” pattern is the “information” the player converts into sound.

 

ONE-NOTE BASS: Muddy and indistinct bass frequencies in a piece of music. Though the musician may be playing all sorts of different individual notes, the listener cannot clearly and distinctly hear them as different and individual. They all sound the same in the recording or when reproduced over a loudspeaker system, so only one note is heard. Thus, “one-note bass.” The reasons for this can be many, including the bass instrument itself sounding muddy, with such a long hangover (sustain) on each note that the next notes played cannot be heard.

 

ONE-OFF, ONE OFF, ONE-OFF c.d. or DVD: When one makes a recording onto a recordable CD, that one copy is said to be a “one-off”.

 

ONE-THIRD OCTAVE: A term referring to frequencies spaced every 1/3 of an octave apart. Technicians and engineers usually test and adjust audio systems by checking frequencies in 1/3 octave increments. This gives a convenient and sufficiently accurate test without having to look at every single audio frequency. It is not often necessary (except when calibrating an analogue tape recorder) to check more than 1/3 octave frequencies to verify that the equipment and/or procedures being used are okay. On most graphic equalisers and on test equipment such as an audio spectrum analyzer the audio frequencies are divided up by 1/3 octaves.

 

ON LINE: 1) Said of electronic audiovisual equipment. The state of being active and prepared for use or operation. Plugged in, connected, and ready to go. Also refers to access to a computer network such as logging onto the Internet. “He is on-line gathering the research data.” 2) When the A/V production truck used for each Gold event is hooked up and in operation, it is said to be “on-line”. 3) Said of the video editing bay where the final edit is done, complete with all visual elements in their final to-be-released form.       

 

ON-LINE BAY: The word “bay” means any compartment or space which is sectioned off for its own purpose or function. It comes from the French word meaning “an opening in a wall”. The On-Line Bay is the final video editing suite at Gold.

 

ON-LINE EDIT: A video edit (not of a film) done after the off-line is approved. It is the final video edit. (See OFF-LINE EDITING for definitions and differences of On-Line and Off-Line.)

       

ON THE AIR: The broadcast or satellite transmission is underway.

 

ON THE BOARD: The mix is “on the board” … meaning that it is in progress or just done but still set up.

 

ON THE FLY: To perform an action without any practice or ability to repeat the action, such as during a live performance where one only has one chance to do an action, record a sound, start a machine, etc. “The engineer made a copy of the camera shot on the fly so it could be instantly played back for the TV audience.”

 

OP AMP: (See OPERATIONAL AMPLIFIER.)

       

OPAQUE:  Lacking detail and transparency. Used to describe the quality of reproduced sound (over loudspeakers) when there seems to be a barrier between the listener and the loudspeaker. The listener cannot hear the details of each sound because they are not clearly recorded, the mix quality is poor, and-or a bad copy is being listened to. The details and clarity sort of smear together and are lost.

 

OPEN: Said of sound. The mix sounds big, each instrument or vocal has space and is not cluttered up. The mix has good imaging, height, depth, and its general “size” is huge. Unrestricted high frequencies.

 

OPEN CHANNEL: A channel on a mix-board which is active and is routed to the monitor system or recording device.  

 

OPEN CIRCUIT: 1) Having a break in a conductor or, for another reason, not having a complete path for electrons to flow. 2) Said of an amplifier, having no connector (wire) plugged into its input connector.  

 

OPEN MEDIA FORMAT: See OMF.

 

OPEN TRACK: An audio recorder having available space upon which to record a sound has an “open track(s)”.

 

OPERATING LEVEL: This is the audio signal level at which a piece of audio equipment is designed to best operate. For more technical information, read on…The two most common operating levels are, +4 dBm (1.23 volts), which is used for professional equipment and -10 dBV (316 millivolts) which is used for home type equipment. Note: The symbol dBm, as covered in the definition of “zero VU” means decibels above or below one milliwatt. dBV means decibels above or below one volt. Unfortunately the audio industry has not agreed upon ONE standard way of measuring signal strength so we encounter different units of measuring the volume of an audio signal. The voltages noted in the parentheses above give a reference in a common unit, the volt.

 

OPERATING SYSTEMS: Generally, an “operating system” refers to the set of internal and external computer commands and routines that allow the computer to manage its components. Most operating systems require additional plug-in cards (circuit boards) or additional software to interface with other devices.

 

OPTICAL ATTENUATOR: Some limiters (such as model LA3A Audio Leveller used on our sound lines) and some compressors, operate using an internal lamp that gets brighter as the volume of the incoming sound signal gets louder and dimmer as it gets lower in volume. The lamp is connected to a circuit that is activated by changes in its brightness. The circuits in the limiter or compressor then work “backwards” with the brightness of the light. (As the light gets brighter, meaning when the audio signal gets louder, the circuits in this type of limiter or compressor act to push the volume down.) An “optical attenuator” is the circuit that does this operation.

 

OPTICAL DISC: A digital disc (CD, DVD, etc.) that can store information in reflective surface etchings.  A laser is an optical device so the discs are referred to as “optical discs”.  

 

OPTICAL FIBRE: See FIBRE OPTICS and INTERNET2.

 

OPTICAL PRINTER: A film printer that works by projecting the image from one film element, such as a negative, onto a print stock film (the unprinted length of film being printed upon, often called “print film”). The printer is called “optical” because it uses a bright light that shines through the film element and precision lenses to project that element’s image onto the piece of print film – just like a projector shines light through film and shows the image on a screen. In the case of the optical printer, the “screen” is the print film. The image on the print is made by projection as opposed to having the negative directly in contact with the print film, as in the case of contact printers. Because of this, optical printers are able to do enlargements and reductions as opposed to a contact printer that only makes a 1 to 1 (size) transfer of an image. Because the image is projected, its size can be varied so that the resulting print may be a “blow-up” or a “reduction” of the original image. The Film Lab’s optical printers are used to “blow up” 16mm film to 35mm film and to “reduce” 35mm film to 16mm. The main uses of Gold’s Optical 1 and Optical 2 printers are for making: 1) The “Reduction Duplicate Negative” - the 16mm inter-negative which will be used to run 16mm copies.

2) 16mm to 35mm blowup – done when producing a film originally shot with a 16mm camera. (The processing of an earlier film shot in 16mm – not 35mm – involves first turning it into the larger sized 35mm format.)

 

OPTICAL RECORDING TECHNOLOGIES: This term refers to the manufacturing processes involved in mass duplicating CDs and DVDs. The process uses a laser to create the first master disc which is subsequently copied and those copies are used to create the discs for sale. For c.d. audio discs, an initial glass disc undergoes a recording process and then a special process to produce a “metallised glass master” - which is then used to produce the “stampers” for the reproduction equipment. (A stamper is used to “stamp” final discs that are then able to be sold to consumers.)

 

OPTICAL SOUND and OPTICAL SOUND HEAD: A small lamp inside a film projector which shines its light through a very specific area on the edge of the film. On the edge, printed into the film, are thousands of very small black lines that perform a similar function to recording tape—they are the soundtrack. As the black lines pass in front of the lamp, because they vary in size, they cause a constantly changing shadow to be cast into a “reader” (a pick-up device called an “optical sound head”) on the other side of the film. The pick-up is able to convert the light changes (shadow changes) into an electrical signal which is then further processed into audible sound which is heard out in the theatre. The lamp is called an “exciter lamp” because it “excites” (activates) the entire process.  Because the process involves the use of light (optics), it is called “optical sound” and the pickup is called an optical sound head. It does the same basic job as a magnetic head on a tape player, only using light. This optical sound process has been in use for many years in the film industry. Most commercial films were processed this way until recently, now being replaced by the various digital audio formats for movie theatres.

 

OPTIMISING A FILE: Optimising means “to improve the performance of something”. This term is in regards to the preparation of audio or video programs intended for Internet use. It is preparing the “file” of information so it will best be carried and distributed on the Internet. For more technical information, read on…Because virtually all audio for the Internet is compressed during the encoding process, it’s more important than ever to have the absolute best audio quality one can achieve in the process of compressing and creating the Internet file. For Internet applications, after the audio program has been mixed and mastered, there are some additional steps which are usually done to “optimise” it for Web playback. This process is known as “optimising a file”. The goal at this step of production is to prepare the program so it plays with the best possible quality over the Internet. One way this is done is by pushing the volume of the program up as loud as possible without distorting. Unfortunately this method can also ruin the dynamic range of the audio.

 

OPTIONAL SURROUND MIX:  A surround sound version of a stereo music release for later release in the surround sound format.

 

OPTO-COUPLER: Any device that functions as an electrical-to-optical or optical-to-electrical transducer. For example, some mixing equipment, especially compressors, use the fluctuation of a small light bulb with which to adjust and perform their electrical functions.

 

ORANGE BOOK: An audio industry publication by Sony and Philips that gives the technical specifications for CD-R (CD-Recordable) and Photo CDs. It’s called the “Orange Book” because the front and back covers of the original publication were orange. (Note: The “Red Book” was the original specification written by Sony and the Philips Corporation in 1980 for the standard commercial c.d. format.) The “Orange Book” was later issued for CD-Rs and Photo CDs, as these are made one at a time by consumers. (They are therefore called “one-off” CDs, and are recorded differently than commercial CDs which are replicated in mass quantities.)

 

ORBAN: Brand name of a company that manufactures audio equipment.

 

ORGANIC: A musical instrument’s sound is said to be “organic” when it subjectively sounds like it has no affiliation or influence with or by electronics. It does not sound like it is being created by electronics. It sounds natural and full of its natural qualities.

 

ORIGINAL CAMERA NEGATIVE: (Abbreviated OCN.) The priceless, and irreplaceable original film footage—the actual negative that was shot (exposed) inside the camera.

       

ORIGINAL (“FIRST”) ANSWER PRINT: At Gold, the Answer Print is an unspliced direct copy of the final cut (edited) original negatives. The Answer Print is made only after final QC approval of a film’s edit. Only then are the original camera negatives cut and assembled precisely per the approved edit. (In Hollywood, the term “Answer Print” answers the question, “is the film done yet???” And so too at Gold.) Note: The running of Answer Prints is strictly regulated as it involves the handling and copying of the irreplaceable original camera negatives. An ORIGINAL or FIRST answer print is a direct copy (print) done immediately of the assembled original negatives. This print is seen by final QC, and is used henceforth for all further comparisons throughout remaining Film Lab production stages, and so QC does not have to look at the Work Print, which has visible splices making it difficult to use for QC purposes. The Answer Print has no splices as it is a full copy of the film printed directly from the assembled negatives.

 

ORIGINAL INSTRUMENT RECORDING: Some musical performers take pride in presenting a piece of music written many years ago playing instruments which were actually made at the time period the piece was written. Instruments hundreds of years old are sometimes used to do this. It gives a realistic recreation of how the piece actually sounded to the first audiences (and composer) when it was written. CDs and DVD music releases of such performances will say, on their packaging, “Original Instrument Recording”, or similar wording to denote this.

 

ORIGINAL NEGS: See ORIGINAL CAMERA NEGATIVES.

 

ORIGINAL RECORDER EQ: When LRH was giving lectures to staff and public starting in the early 50’s through to the mid 80’s, a great variety of different audio tape recording machines were used. LRH pointed out that the best machine to play a recorded tape upon was the machine which made the actual recording. When efforts to restore and mix the lectures commenced in the early 80’s an extensive research project found and obtained most of the tape recorders which had ever been used throughout the years to record LRH. Testing discovered that each recorder actually had a characteristic way it reproduced sound, and that this could be duplicated in PT. Tests were first done on each machine to precisely determine what settings on an equaliser would exactly duplicate the character of the original recording machine itself. These EQ settings were plotted (written on graphs) using very precise audio analysis equipment. This plot was then called, the “original recorder EQ”. Each lecture, when it is about to be restored and mixed, is first noted as to what original recording machine upon which it was recorded. The plot for that machine is duplicated precisely with a high quality equaliser, and the lecture is first sent through that equaliser to tailor its sound so as to match how the original recording machine created the sound of the tape. This technology is one of the major aspects of “Clearsound” as regards to LRH original lecture recordings being produced to sound as if one was there, present for the original lecture itself.

 

ORTHOCHROMATIC FILM: The prefix “ortho-” as used in this term means “right, correct” and the suffix “-chroma” means “colour”.  “Orthochromatic” refers to an older type of black and white film sensitive to both green and blue light, but “blind” to red. Because it was sensitive to two colours and could produce more shades of gray than its predecessor, monochromatic film, orthochromatic was marketed as producing a more correct looking film image with enough shades of gray to form natural-looking black and white images. With orthochromatic film, green and blue colours photograph in varying shades of gray, but reds appear as black. The first film used for silent motion pictures was  monochromatic, which  was  sensitive to only  blue light, and  made extremely “black and white” images with virtually no shades of gray in between. Around 1918, orthochromatic film became available, offering improved gradations from the darkest to the brightest images in the photographed scene. However, due to orthochromatic film’s insensitivity to red light, the image, like monochrome film, had a tendency to look highly contrasted, lacking finer shadings and details existing in natural brightness and shadow. (Note: Because of this limitation, heavy make-up had to be used on performers to neutralise the red skin tones so the actors’ faces wouldn’t appear black—unless, of course they were black actors!) For more technical information, read on…Orthochromatic film, like monochromatic, is “fast film” in that its emulsion is extremely sensitive to light and it exposes very quickly with relatively small amounts of light and small openings in the camera’s aperture. Because of their “speed”, these films could be shot with a small aperture (camera lens opening).  It is an optical fact that the smaller the aperture, the more objects both closer up and further away from the camera will be in focus.) Thus orthochromatic (and monochromatic) films allow the photographed image, both background and foreground objects and actors, to be highly defined—in focus, sharp and clear. (Note that this is not always desirable. Many cinematographers prefer to shoot a scene with the foreground and background not sharply in focus and only the centre of attention—the place where the camera is precisely focused—highly defined.) Panchromatic film came into use in 1926. This newer type of black and white film was sensitive to all parts of the colour spectrum, including red, hence the image was far more natural with highly improved and varied shades of gray. However, because panchromatic film was slower (meaning less sensitive to brightness of light, thus requiring a larger aperture opening) the large “depth of focus” (backgrounds and foregrounds in focus as well as the main subject of the camera’s focus) achieved with monochromatic and orthochromatic films was no longer easily achieved. Orthochromatic film is still used in some film applications by still photographers who want to produce pictures that have high contrast between the dark and light areas of the image without many shades and variations of gray. Orthochrome motion picture film is no longer made, and those who want its look for black and white cinematography use panchromatic cine film. (Greater or lesser degrees of contrast are achieved with lighting and film lab developing and printing.)

 

OSCILLATOR:  1) A signal generator whose output is a pure sine wave. Generally the output frequency may be varied continuously or in discrete steps over the audio frequency bandwidth. 2) In synthesizers and other electronic musical instruments, an oscillator is an internal electronic circuit that is used to add to a sound already created by the synthesizer. One starts off with a basic sound and then sends it through the oscillators of the instrument to add different qualities to that sound.

 

OTARI: The name of a company that manufactures many different types of audio recording equipment, both analogue and digital.

 

OTARI BASS MOD: See BASS MOD.

 

OUTBOARD, OUTBOARD MIXING EQUIPMENT: Refers to audio mixing equipment that is not built into the mix-board itself but is “outboard”—meaning located external to the mix-board.

 

OUTLETS: Locations and terminals which sell and/or utilise audiovisual products.

 

OUT OF SYNCH: Said when the pictures of a film or video do not match up in time with the soundtrack or when two or more audiovisual machines are not running together in perfect time.

 

OUTPUT: 1) The place that the audio signal goes out of a piece of equipment. Examples would be the speaker output from an amplifier or an output connector on the back of a mix-board which sends the mix to a tape recorder so it can be recorded. An output is the path through which audio passes from one device to another. 2) The actual audio signal itself exiting a component is said to be “the output”.

 

OUTPUT BUS (OR BUSS): See BUSS and CONSOLE OUTPUT BUSS.

 

OUTPUT LEVEL: A measure of how strong an audio or video signal produced by a component is, usually in relation to the strength of the signal put into it.   

 

OUTPUT CALIBRATION FOR SPEAKER AMPLIFIERS: The use of a test tone and calibrated reference metre in a studio to verify that one’s loudspeakers and their amplifiers are playing sound at the exact same volume and that their volume is precisely correct to the reference metre.

       

OUTPUT STAGE: Inside audio electronic equipment, such as amplifiers and preamplifiers, the final part of the circuit which boosts the signal just before it leaves the equipment to be passed on to another piece of gear.

 

OUTPUT TO FILM: This refers to a process where computer generated images, such as special effects and footage processed by a computer for restoration is output to film.

 

OUTS: The connection points on a piece of electronic audiovisual equipment from which the signals leaving the unit pass for sending on to other equipment.  There are may different output connections (“outs”) used. The most common in the audio industry include XLR, Phone Jack, RCA (phono), DB-25 and Terminal Strip.

 

OUT-TAKE: An audio recording, video recording or cine shot not used because a better recording of the same performance was obtained.

 

OVEN-CONTROLLED CRYSTAL OSCILLATOR: When a crystal is sent electricity it oscillates at very precise intervals. However, if the temperature changes, its rate of oscillation can vary. To keep the crystal at a precise temperature, a small heater (oven) is placed near the crystal to keep its temperature as close to exact as possible. Functions that computers and computerised audiovisual equipment do are, in this way, kept much more stable while they are operating.

 

OVER-BIAS: (See BIAS and BIAS FREQUENCY.) Overbias at high frequencies is used in calibrating a tape machine for a specific brand and type of tape. This is done by an audio technician or operator when calibrating an analogue audio tape recorder.

 

OVER-BLOWN: Said to describe sound. “Overblown” means that the sound is bloated, excessively fat and rich. Too much bass or upper bass.

 

OVER-CRANK: To shoot (on film or video) at a faster speed so that the resulting image is played back in slow motion. “Over” in this case means “in excess” and “crank” means “to rotate”. Thus over crank refers to the motion of the film or video camera mechanism that moves the film or videotape through the camera. (Compare UNDER CRANK.)

 

OVER-DAMPED: Pertaining to the audible effects of excessive woofer damping. (See DAMPING.)

 

OVER-DRIVING: To overload the input of an amplifier, especially in instrument amplifiers, such as for electric guitars, to obtain a controlled distortion. Often used in rock guitar—live and recorded.

 

OVER-DUB RECORDING: The process of recording additional sounds while listening to previously recorded sounds. For example, it allows songs to be built up track-by-track by playing or singing along with what has already been recorded.      

 

OVERFLOW, OVERFLOW LOCATION: An additional location at the event venue used for any possible excess of people who don’t fit into the main event hall. The overflow room is set up with a video and audio system that plays a live feed of the event.       

OVERLOAD: To put too much signal level into a piece of equipment or a loudspeaker, thereby causing distortion.

OVER MODULATION: Exceeding the maximum permissible amplitude for recording or transmission. Distortion may be expected.

 

OVERS (AN “OVER”): Refers to digital recording equipment. When it tries to record a signal that is too loud, the signal is said to go “over” what the digital recorder can handle. It then distorts. An “over” is a distortion caused by the volume of the signal going so loud that it exceeds the digital capabilities of the equipment. Sometimes an “over” can occur per the equipment’s metres, even though no distortion may be audible. Often overs are quite easily heard as a cracking or thumping type of distortion. Most digital metres register and show when an over has happened, but they are set in such a way that one actually has a bit more room (“headroom”) to go before distortion actually happens. It is not uncommon for very fast transients, like a quick drum hit, to register an over, but not distort. If an over occurs, as registered on the metre, one has to listen to verify the program did not distort.

 

OVERSAMPLING: “Oversampling” is a feature on many different types of digital audiovisual equipment. One will see it written on the front of some c.d. players, for example. It is of note that “oversampling” does not merely mean that a high sampling rate is used. It means that a piece of equipment is taking the original sampling rate and multiplying it so it can process the signal more accurately. The “over” part of oversampling means that the original sampling rate is multiplied. Sampling rates are commonly multiplied by 4X or 8X in digital audio, but oversampling is sometimes done by as much as 64X or more. This is done in an effort to more cleanly and accurately reproduce the original sound.

For a more detailed definition, read on… Take a familiar sampling rate of 44.1k as used to create a CD. Digital audio recorders that record at this rate have a maximum of 44,100 times per second at which to make a sample of the audio. While this may seem like a lot, realise that one individual 20,000 Hz high frequency sound is vibrating 20,000 times per second. A 20,000 Hz sound is completing 20,000 cycles each second. And each one of those cycles is a vibration back and forth. So, minimally two samples are needed for each vibration of the sound to take a somewhat accurate “picture” of its motion. Digital equipment has to represent each one of those vibrations with bits. A music c.d. has 16 bits available for each sample. In sampling a single 20k sound, one can see that much of the equipment’s sampling recording capability is used up – and that’s just to record one single sound at 20k. What happens if there is more than just that one 20k sound to record in a given instant? The recorder does what it can to sample the one sound and it produces a high frequency noise in a failed attempt to sample the rest. To prevent that noise from being heard, digital equipment has electronic circuits that filter the noise and cut it off. Unfortunately, these filters can also audibly reduce the high frequency sounds of the audio program. Oversampling is a solution to this. If that original 44.1kHz sampling rate was increased by 2x to 88.2kHz, then the equipment’s filters would not have to cut off any audible high frequencies. Oversampling doesn’t change the original number of samples taken by the original recorder. It does change how that original 16 bit, 44.1kHz signal is processed internally so that any filters used don’t further degrade the signal by chopping off some of the high frequencies. When you see 2x, 4x, 8x, 64x, etc. “over sampling” written on a c.d. player, d,v.d. player or other digital audio device, the above is what it does with the sound to record and-or reproduce it as accurately as possible by digital methods.

 

OVERSHOOT: The term “overshoot” concerns a square wave, a waveform highly usable to help test the performance of audio electronic equipment. If the wave is not a perfect square as shown on an oscilloscope, one knows right away there is something wrong with that piece of equipment, wire, etc. It is a very demanding test of hi-fi equipment and therefore particularly useful. When looking at a square wave on an oscilloscope, the ideal form of the wave is perfectly flat on its top and bottom. It literally looks like a square on the screen. “Overshoot” can appear on either the left-hand and/or right-hand edges of a square wave displayed on the scope.  The overshoot looks like a spike or a small hump extending up. Some types of equipment are more prone to overshoot than others, for example analogue tape recorders. Overshoots are caused by phase shifts in the audio signal

 

“OVER THE AIR TELEVISION”: This is a term used to differentiate between the different ways to receive t.v. “Over the air television” refers to the use of an antenna and picking up t.v. broadcasts in that manner. One can also receive cable tv, satellite tv, etc. see also “Free to air television.”

 

OVERTONE: A harmonic that is higher in frequency than the fundamental pitch or tone. For example, if the fundamental tone is at 200Hz, overtones would be at 400Hz, 800Hz, 1600Hz, 3200Hz, etcetera.

 

OXIDE: The magnetic coating on recording tape. Called this because the most common coating is from iron oxide (rust).

 

__________