Information about Wow (recording)
Wow is a relatively slow form of flutter (pitch variation) which can affect both gramophone records and tape recorders. In the latter, the collective expression wow and flutter is commonly used.
In a gramophone record, the ideally constant angular velocity of the platter translates into a linear velocity of the stylus relative to the record groove depending on the distance from the rotational axis of the record (that is, the spindle hole). The velocity follows the relationship
. The linear velocity of the stylus is greater when it is further out and less when it is towards the center of the record.
If the hole is not centered exactly, the linear velocity of the stylus, instead of dropping gradually as the groove spirals towards the center, varies every revolution to be too high (resulting in a higher pitch) when the stylus is further out, and too low when the stylus is further inwards (resulting in a lower pitch). Obviously, the more eccentric the positioning of the spindle hole, the greater the pitch variation.
The cause for "wow"-effects on a warped disc is basically the same; a variation in the linear velocity of the stylus relative to the disc. This can be by either radial warping (similar to the eccentric hole case) or by the disc warping out of its plane. This would mean that the stylus would have to travel faster over the warped section as it must displace both in and out of the plane of the disc.
Gramophone records
When playing gramophone records, wow is a once-per-revolution pitch variation which could result from warping of the record or from a spindle hole that was not precisely centered.In a gramophone record, the ideally constant angular velocity of the platter translates into a linear velocity of the stylus relative to the record groove depending on the distance from the rotational axis of the record (that is, the spindle hole). The velocity follows the relationship
. The linear velocity of the stylus is greater when it is further out and less when it is towards the center of the record.
If the hole is not centered exactly, the linear velocity of the stylus, instead of dropping gradually as the groove spirals towards the center, varies every revolution to be too high (resulting in a higher pitch) when the stylus is further out, and too low when the stylus is further inwards (resulting in a lower pitch). Obviously, the more eccentric the positioning of the spindle hole, the greater the pitch variation.
The cause for "wow"-effects on a warped disc is basically the same; a variation in the linear velocity of the stylus relative to the disc. This can be by either radial warping (similar to the eccentric hole case) or by the disc warping out of its plane. This would mean that the stylus would have to travel faster over the warped section as it must displace both in and out of the plane of the disc.
Tape recorders
A similar problem can occur with tape recorders. The changes in frequency are caused by irregular tape motion during recording or playback. For example, a change in the angular velocity of the capstan, or dragging of the tape within an audio cassette shell. In these cases, the terms "wow and flutter" are often referred to together. A typical modern cassette recorder may have a wow and flutter specification of 0.08%Video recording
A similar problem can also occur in videotape recordings, causing the picture to jitter slightly, or the top of the picture to wobble. This is known as flagwaving.See also
In electronics and communication, flutter is the rapid variation of signal parameters, such as amplitude, phase, and frequency. In structures, the term refers to rapid periodic motion caused by interaction of structural mass, stiffness, and aerodynamic forces.
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gramophone record (also phonograph record, or simply record) is an analogue sound storage medium consisting of a flat disc with an inscribed modulated spiral groove starting near the periphery and ending near the center of the disc.
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tape recorder, tape deck, reel-to-reel tape deck, cassette deck or tape machine is an audio storage device that records and plays back sound using magnetic tape, either wound on a reel or in a cassette, for storage.
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Pitch is the perceived fundamental frequency of a sound. While the actual fundamental frequency can be precisely determined through physical measurement, it may differ from the perceived pitch because of overtones, or partials, in the sound.
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Constant angular velocity (CAV) describes the motion of a body rotating at a constant angular velocity, because as it rotates it moves through a constant angle per unit time. CAV is one method of writing or reading information from a rotating data disc.
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stylus (plural: styli or styluses) is a writing utensil. The word is also used for a computer accessory (PDAs). It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Many styluses are heavily curved to be held more easily.
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Capstans are rotating spindles used to move recording tape through the mechanism of a tape recorder. The tape is threaded between the capstan and one or more rubber-covered wheel, called a "pinch roller", which presses against the capstan, thus providing friction necessary for the
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Compact Cassette
Typical 60-minute Compact Cassette
Media type: magnetic tape
Encoding: analog signal
Capacity: 23 minutes per side (C46)
30 minutes per side (C60)
45 minutes per side (C90)
50 minutes per side (C100)
60 minutes per side (C120)
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Typical 60-minute Compact Cassette
Media type: magnetic tape
Encoding: analog signal
Capacity: 23 minutes per side (C46)
30 minutes per side (C60)
45 minutes per side (C90)
50 minutes per side (C100)
60 minutes per side (C120)
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Videotape is a means of recording images and sound onto magnetic tape as opposed to movie film. In most cases, a helical scan video head rotates against the moving tape to record the data in two dimensions, because video signals have a very high bandwidth, and static heads would
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Time base correction is a technique to reduce or eliminate errors caused by mechanical instability present in analog recordings on mechanical media, including video tape recorders and videocassette recorders.
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Rumble measurement is carried out on turntables (for vinyl recordings) which tend to generate very low frequency noise originating from the centre bearing and from drive pulleys or belts, as well as from irregularities in the record disc itself.
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Edison cylinder phonograph ca. 1899]] The phonograph, or gramophone, was the most common device for playing recorded sound from the 1870s through the 1980s.
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Terminology
Usage of these terms is not uniform across the English-speaking world (see below)...... Click the link for more information.
Wow and flutter measurement is carried out on audio tape machines, cassette recorders and players, and other analog recording and reproduction devices with rotary components (e.g. movie projectors, turntables (vinyl recording), etc.).
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