Genlock / House Sync
Definition
Genlock (generator locking) is the synchronisation of video equipment to a common timing reference, so that frames and lines start at the same instant on every device. The reference, often called house sync, is produced by a sync pulse generator and distributed to cameras, switchers, recorders, capture cards and LED processors. In standard definition the reference is black burst. In HD it is usually tri-level sync, defined with the HD formats in SMPTE ST 274 and ST 296, although many HD devices also accept black burst. In IP facilities built on SMPTE ST 2110, the same role is played by the PTP clock (SMPTE ST 2059). When sources are not synchronised, a switcher has to realign each input with a frame synchroniser, which generally adds up to one frame of delay, or the cut produces a visible disturbance.
In the field
A flash, a roll or a short black on a camera cut usually indicates that a source is not locked. The usual checks are that the reference signal reaches the camera's genlock input, that the camera is set to external sync, and that the reference format matches the project format.
Related lessons
Sources
- Tektronix, Adjusting system timing and achieving synchronization : référence commune, black burst et tri-level, calage des équipements · download.tek.com
- Wikipédia, Tri-level sync : synchro tri-level des formats HD (pointeur secondaire) · en.wikipedia.org
- Wikipédia, SMPTE 274M : formats HD 1080 lignes (pointeur secondaire) · en.wikipedia.org
- Wikipédia, SMPTE ST 296 : formats HD 720 lignes (pointeur secondaire) · en.wikipedia.org
- Wikipédia, SMPTE 2110 : vidéo professionnelle sur IP, synchronisée par PTP selon SMPTE ST 2059 (pointeur secondaire) · en.wikipedia.org
- SMPTE, Synchronization of SMPTE ST 2110 Signals (poster) : synchronisation par PTP selon SMPTE ST 2059-1 et ST 2059-2 · smpte.org
- Wikipédia, Genlock : principe et générateur de synchro maison (pointeur secondaire) · en.wikipedia.org