View source for Y/C DUB color-under

'''Y/C DUB color-under''' is a separated Y/C video signal format used on U-matic, VHS, Betamax, and other tape formats 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 used during tape recording rather than being upconverted to the standard 3.58 MHz (NTSC) or 4.43 MHz (PAL) subcarrier.

== Overview ==

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.

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.

== Color-Under Frequencies ==

{| class="wikitable"
! Format !! Chrominance Frequency
|-
| U-matic low-band || 685.546 kHz
|-
| U-matic hi-band / SP || 983.803 kHz
|-
| VHS / VHS-C || 629 kHz
|-
| S-VHS / S-VHS-C || 629 kHz
|-
| Betamax || 688 kHz
|-
| Video8 || 732 kHz
|}

Equipment labels may refer to specific frequencies (e.g., "Y/C-688" for U-matic low-band/Betamax frequency) or use general terms like "DUB" to indicate color-under Y/C support.

== Connector ==

The DUB signal is typically carried on a [[Hirose 7-pin DUB]] connector on U-matic equipment and some professional VHS decks. Some time base correctors and transcoders (such as the [[Digital Processing Systems DPS-210]]) provide both [[Hirose 7-pin DUB]] connectors for direct VTR connection and [[BNC]] connectors with separate Y and C for flexible signal routing.

== Y/C-688 ==

'''Y/C-688''' is a common designation for U-matic color-under signal, referring specifically to the 688 kHz (more precisely 685.546 kHz) chrominance carrier frequency used by U-matic low-band decks. The name derives from the "Y/C" (luminance/chrominance) component separation combined with the nominal carrier frequency.

The term "Y/C-688" was used by some manufacturers and in professional documentation to distinguish U-matic DUB connections from standard S-Video (which uses a 3.58 MHz subcarrier for NTSC). The AMIA Cable Bible notes that Y/C-688 predates S-Video as a separated Y/C format, was first seen on 3/4" U-matic decks, and continued to be used on professional Betacam and VHS/S-VHS decks.<ref name="cable-bible">{{cite web |url=https://amiaopensource.github.io/cable-bible/#yc-688 |title=Y/C-688 ("Dub") |website=The Cable Bible |publisher=AMIA Open Source |access-date=2026-02-07}}</ref>

An important characteristic of Y/C-688 connections is that different devices modulated chrominance at different frequencies depending on the tape format—making signals from one Y/C-688-capable deck potentially incompatible with another, or with S-Video devices.<ref name="cable-bible" /> This is why the more general term "Y/C DUB color-under" is preferred when describing the signal type, as it encompasses all color-under frequencies without implying a specific modulation standard.

== See Also ==

* [[S-Video (Y/C)]] — Standard Y/C with upconverted chrominance
* [[Hirose 7-pin DUB]] — Common connector for DUB signals
* [[Composite (CVBS)]] — Composite video signal format

[[Category:Video signal formats]]

== References ==
<references />