Understanding Sync
Retro Access specializes in professional-grade BNC and SCART cables carrying RGBs signals.
RGBs signals are desirable in analog video systems for their superior picture quality and wide compatibility with professional video monitors and upscaling devices for use with HDTVs. RGBs uses four channel video signals which include Red, Green, Blue and Sync. Common connector types include D-sub (DE-15, HD15), BNC and SCART.
For alternate signal types, we recommend the following cables:
- YPbPr “Component” HD Retrovision
- CVBS “Composite” Retro Frog
Separate Sync (H+V)
Sync is separated into dedicated channels for horizontal and for vertical sync signals. This is a 5 channel signal (RGBHV).
This is used in VGA and some high-resolution arcade monitors. Separate sync signals provide a better level of precision required for high resolution.
Separate Sync is generally not used by retro gaming hardware or typical 15 kHz (240p / 480i) signals.
Composite Sync (CSync)
Not to be confused with “Composite Video” (CVBS) signals, Composite Sync (CSync) also known as Pure Sync is a dedicated sync channel combining both horizontal and vertical sync, thus the origin of the term “composite”. The signal does not contain any additional picture information.
Unlike Composite Video (CVBS) and Sync on Luma, CSync can have two voltage levels: TTL (5V) sync and 75 Ω (ohm) sync.
TTL or logic-level signals have a peak-to-peak voltage of 5V. Meanwhile, the SCART standard specifies 75 ohm sync should have a nominal peak-to-peak voltage of 0.3V. Sending a TTL sync signal to a consumer-grade device (e.g. television or scaler) exposes it to 15x the expected voltage and 7x the generally accepted maximum safe voltage of 0.7V for 75 ohm CSync. Retro Access cables are designed to attenuate TTL level CSync to a safe 75 ohm.
CSync is regarded as the “cleanest” sync signal, as nothing else is along for the ride. It can be preferred for RGB SCART scaling devices or professional displays like PVM/BVM. Extron CrossPoint matrix switchers require CSync to operate.
Sync on Composite Video (CVBS)
Composite Video (CVBS) also known as Composite Video Baseband Signal, or Color Video Blanking Sync carries picture information with sync embedded into a single channel.
The major benefit is nearly all analog video consumer devices output CVBS, therefore CVBS is generally universally available. Another nice benefit is that choosing CVBS for the sync signal on your SCART cable opens the ability to switch between RGBs and Composite Video downstream on your scaler or display.
The downside to using Sync on Composite Video is it shown to more aggressively introduce audio-visual noise on poorly shielded cables. However, with 75 ohm Mini-Coax, all signal lines are sufficiently shielded to virtually eliminate coupling and crosstalk, minimizing interference while retaining signal flexibility.
When using Mini-Coax cables, you will experience an identical picture quality as CSync or Luma when choosing CVBS.
Sync on Composite Video cannot be used with the Extron CrossPoint.
Sync on Luma
Sync is embedded in the luminance (Y) channel of S-Video (Y/C) or Component (YPbPr).
A Sync on Luma signal is considered cleaner than CVBS since it lacks color (Chroma) info. Sync on Luma is considered an excellent choice due to wide compatibility, with notable exception to the Extron CrossPoint.
Sync on Green (SoG)
Often referred to as RGsB or Sync on Green (SoG), this is found on the PlayStation 2 and some computer graphics systems. With SoG, the Sync signal is embedded in the green channel of RGB. It is therefore a three channel signal instead of four like conventional RGBs configurations.
The PlayStation 2 normally outputs Sync on Composite and Sync on Luma when in 480i (interlaced, 15kHz horizontal scan rate) mode. However, when 480p (progressive scan, 31kHz horizontal scan rate) mode is enabled the console disables the CVBS and Luma outputs and switches to using Sync on Green.
Retro Access RGB SCART cables will successfully carry a Sync on Green signal provided your device supports this signal type. Sync on Green is not compatible with the Extron CrossPoint, XRGB-mini Framemeister or RetroTINK-5X Pro.