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| '''Y/C-688''' is a color-under Y/C video signal format used on U-matic VTRs and some professional VHS equipment via DUB connectors. Like standard [[S-Video (Y/C)]], the signal carries luminance (Y) and chrominance (C) on separate conductors, but the chrominance subcarrier remains at the color-under frequency of approximately 688 kHz (NTSC low-band) rather than being upconverted to the standard 3.58 MHz (NTSC) or 4.43 MHz (PAL) subcarrier.
| | #REDIRECT [[Y/C DUB color-under#Y/C-688]] |
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| == Overview ==
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| During recording, U-matic and VHS-family formats downconvert the chrominance subcarrier to a lower frequency for storage on tape — a process known as color-under recording. On playback, the VTR's internal circuitry normally upconverts the chrominance back to the broadcast standard frequency before outputting composite or S-Video. The DUB connector bypasses this upconversion step, providing the raw color-under signal directly.
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| This approach preserves signal quality by avoiding an unnecessary decode/re-encode cycle, making it ideal for VTR-to-VTR dubbing and for feeding time base correctors that accept color-under input natively.
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| == Color-Under Frequencies ==
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| {| class="wikitable"
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| ! Format !! Chrominance Frequency
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| | U-matic low-band || 685.546 kHz
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| | U-matic hi-band / SP || 983.803 kHz
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| | VHS / VHS-C || 629 kHz
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| | S-VHS / S-VHS-C || 629 kHz
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| | Betamax || 688 kHz
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| | Video8 || 732 kHz
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| |}
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| Although "688" specifically refers to the approximate U-matic low-band and Betamax frequency, the term Y/C-688 is commonly used as a general label for color-under DUB connections on professional equipment, sometimes encompassing other color-under frequencies as well.
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| == Connector ==
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| The DUB signal is typically carried on a [[Hirose 7-pin DUB]] connector on U-matic equipment, or on a [[Mini-DIN-4]] connector on some professional VHS decks. Some time base correctors and transcoders (such as the [[Digital Processing Systems DPS-210]]) accept DUB input via [[BNC]] connectors with separate Y and C connections.
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| == See Also ==
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| * [[S-Video (Y/C)]] — Standard Y/C with upconverted chrominance
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| * [[Hirose 7-pin DUB]] — Common connector for DUB signals
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| * [[Composite (CVBS)]] — Composite video signal format
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| [[Category:Video signal formats]]
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