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Wow is a relatively slow form of flutter (pitch variation) that can affect gramophone records and tape recorders. For both, the collective expression wow and flutter, or sometimes flutter and wow, is commonly used.
When playing gramophone records, wow is a once-per-revolution pitch variation which could result from warping of the record or from a pressing plate that was not precisely centered.
If the grooves are not centered exactly relative to the spindle hole, 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). The more eccentric the positioning, 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.
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 a reel or audio cassette shell. The terms "wow and flutter" are often referred to together, flutter being a higher-rate version of wow.
Scrape flutter—a high frequency flutter of above 1000 Hz—can sometimes occur from the tape vibrating as it passes over a head, as a result of rapidly interacting stretch in the tape and stiction at the head. It adds a roughness to the sound that is not typical of wow and flutter, and damping devices or heavy rollers are sometimes employed on professional tape machines to prevent it. Scrape flutter measurement requires special techniques, often using a 10 kHz tone.
A typical modern cassette recorder may have a wow and flutter specification of 0.08%.
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.
Methods of digital signal processing have been developed that correct wow and flutter by tracking various spurious things on the tape or film, which can be re-purposed as timing references. A system developed by Plangent Processes substantially reduces wow and flutter of very high rates to extremely low levels, with a substantial improvement in quality. The software Capstan by Celemony analyzes the already digitalized musical material and uses varispeed playback to eliminate wow and flutter.
A phonograph, in its later forms also called a gramophone or since the 1940s called a record player, is a device for the mechanical recording and reproduction of sound. The sound vibration waveforms are recorded as corresponding physical deviations of a spiral groove engraved, etched, incised, or impressed into the surface of a rotating cylinder or disc, called a "record". To recreate the sound, the surface is similarly rotated while a playback stylus traces the groove and is therefore vibrated by it, very faintly reproducing the recorded sound. In early acoustic phonographs, the stylus vibrated a diaphragm which produced sound waves which were coupled to the open air through a flaring horn, or directly to the listener's ears through stethoscope-type earphones.
In electronics and communication, flutter is the rapid variation of signal parameters, such as amplitude, phase, and frequency. Examples of electronic flutter are:
The Compact Cassette or Musicassette (MC), also commonly called the tape cartridge, tape cassette, audio cassette, cassette tape, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. It was developed by Philips in Hasselt, Belgium, and introduced in September 1963. Compact Cassettes come in two forms, either already containing content as a prerecorded cassette (Musicassette), or as a fully recordable "blank" cassette. Both forms are reversible by the user.
An audio tape recorder, tape deck, or tape machine is a sound recording and reproduction device that records and plays back sounds usually using magnetic tape for storage. In its present-day form, it records a fluctuating signal by moving the tape across a tape head that polarizes the magnetic domains in the tape in proportion to the audio signal. Tape-recording devices include the reel-to-reel tape deck and the cassette deck, which uses a cassette for storage.
A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. The first was Dolby A, a professional broadband noise reduction system for recording studios in 1965, but the best-known is Dolby B, a sliding band system for the consumer market, which helped make high fidelity practical on cassette tapes, which used a relatively noisy tape size and speed. It is common on high fidelity stereo tape players and recorders to the present day. Of the noise reduction systems, Dolby A and Dolby SR were developed for professional use. Dolby B, C, and S were designed for the consumer market. Aside from Dolby HX, all the Dolby variants work by companding, or compressing, the dynamic range of the sound during recording, and expanding it during playback.
A cassette deck is a type of tape machine for playing and recording audio cassettes. The consumer electronics industry formerly used the term deck to distinguish them from a tape recorder, the "deck" being part of a stereo component system, while a "tape recorder" was more portable and usually had a self-contained power amplifier.
Sound can be recorded and stored and played using either digital or analog techniques. Both techniques introduce errors and distortions in the sound, and these methods can be systematically compared. Musicians and listeners have argued over the superiority of digital versus analog sound recordings. Arguments for analog systems include the absence of fundamental error mechanisms which are present in digital audio systems, including aliasing and quantization noise. Advocates of digital point to the high levels of performance possible with digital audio, including excellent linearity in the audible band and low levels of noise and distortion.
A phonograph record, or simply a record, is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts near the periphery and ends near the center of the disc. At first, the discs were commonly made from shellac, with earlier records having a fine abrasive filler mixed in. Starting in the 1940s polyvinyl chloride became common, hence the name vinyl. In the mid-2000s, gradually, records made of any material began to be called vinyl records, or simply vinyl.
Audio system measurements are a means of quantifying system performance. These measurements are made for several purposes. Designers take measurements so that they can specify the performance of a piece of equipment. Maintenance engineers make them to ensure equipment is still working to specification, or to ensure that the cumulative defects of an audio path are within limits considered acceptable. Audio system measurements often accommodate psychoacoustic principles to measure the system in a way that relates to human hearing.
Reel-to-reel audio tape recording, also called open-reel recording, is the form of magnetic tape audio recording in which the recording medium is held on a reel that is not permanently mounted in an enclosed cassette. In use, the supply reel containing the tape is placed on a spindle or hub; the end of the tape is manually pulled out of the reel, threaded through mechanical guides and a tape head assembly, and attached by friction to the hub of the second, initially empty takeup reel.
A video tape recorder (VTR) is a tape recorder designed to record and play back video and audio material from magnetic tape. The early VTRs were open-reel devices that record on individual reels of 2-inch-wide tape. They were used in television studios, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. Beginning in 1963, videotape machines made instant replay during televised sporting events possible. Improved formats, in which the tape was contained inside a videocassette, were introduced around 1969; the machines which play them are called videocassette recorders.
A skip occurs when a phonograph (gramophone), cassette tape or compact disc player malfunctions or is disturbed so as to play incorrectly, causing a break in sound or a jump to another part of the recording.
A rumble is a continuous deep, resonant sound, such as the sound made by heavy vehicles or thunder. In the context of audio reproduction rumble refers to a low frequency sound from the bearings inside a turntable. This is most noticeable in low quality turntables with ball bearings. Higher quality turntables use slide bearings, minimizing rumble.
Measurement of wow and flutter is carried out on audio tape machines, cassette recorders and players, and other analog recording and reproduction devices with rotary components This measurement quantifies the amount of 'frequency wobble' present in subjectively valid terms. Turntables tend to suffer mainly slow wow. In digital systems, which are locked to crystal oscillators, variations in clock timing are referred to as wander or jitter, depending on speed.
The history of sound recording - which has progressed in waves, driven by the invention and commercial introduction of new technologies — can be roughly divided into four main periods:
The dbx Model 700 Digital Audio Processor was a professional audio ADC/DAC combination unit, which digitized a stereo analog audio input into a bitstream, which was then encoded and encapsulated in an analog composite video signal, for recording to tape using a VCR as a transport. Unlike other similar pieces of equipment like the Sony PCM-F1, the Model 700 used a technique called Companded Predictive Delta Modulation, rather than the now-common pulse-code modulation. At the time of its introduction in the mid-1980s the device was the first commercial product to use this method, although it had been proposed in the 1960s and prototyped in the late '70s.
The LP is an analog sound storage medium, a phonograph record format characterized by a speed of 33 1⁄3 rpm, a 12- or 10-inch diameter, and use of the "microgroove" groove specification. Introduced by Columbia in 1948, it was soon adopted as a new standard by the entire record industry. Apart from a few relatively minor refinements and the important later addition of stereophonic sound, it remained the standard format for record albums until its gradual replacement from the 1980s to the early 21st century, first by compact discs and then by music downloads and streaming.
A tape transport is the collection of parts of a magnetic tape player or recorder that move the tape and play or record it. Transport parts include the head, capstan, pinch roller, tape pins, and tape guide. The tape transport as a whole is called the transport mechanism.
The Walkman DD was an early series in Sony's Walkman line of portable audio cassette players. The "DD" stood for 'disc drive', with the unit's main motor being directly coupled to the 'disc' of the capstan flywheel assembly while lying perpendicular to it within the unit. This feature was later shared with the Walkman Professional series.
The Nakamichi Dragon is an audio cassette deck that was introduced by Nakamichi in 1982 and marketed until 1994. The Dragon was the first Nakamichi model with bidirectional replay capability and the world's first production tape recorder with an automatic azimuth correction system; this feature, which was invented by Philips engineers and improved by Niro Nakamichi, continuously adjusts the azimuth of the replay head to minimize apparent head skew and correctly reproduce the treble signal present on the tape. The system allows the correct reproduction of mechanically skewed cassettes and recordings made on misaligned decks. Apart from the Dragon, similar systems have only been used in the Nakamichi TD-1200 car cassette player and the Marantz SD-930 cassette deck.