It seems rude not to namecheck the Serial Digital Interface (or SDI) on Day 16 of our Advent Calendar.
It’s everywhere these days – we even demoed it at NAB and IBC this year as part of our demonstration on connectivity – and is a brilliantly clever use of unwanted and unloved surplus space. The SDI signal allows for 16 x 48kHz channels of audio to be embedded in the horizontal blanking periods, which can be split up in a variety of ways: 8 x stereo signals, 2 x 5.1 signals, 2 x 5.1 signals and 2 x stereo downmixes…as long as there are less that 16 channels.
It also gives us an opportunity to link to the IABM Broadcast and Technology Industry Guide, an excellent introductory guide to broadcast technology and a rather generous glossary of broadcast terms, which you can learn and impress your peers with at various industry parties.
Their SDI entry runs thusly:
Serial Digital Interface (SDI) Serial Digital Interface carries uncompressed digital video, multiple tracks of embedded audio and ancillary data over the ubiquitous 75-ohm coax cable,terminated in a BNC connector. As the demands of television have grown so has SDI. Today there are three types. SDI SMPTE 259M – for SD 4:2:2 digital television, is based on a 270 Mb/s transfer rate. This is a 10-bit, scrambled, polarity-independent interface, with common scrambling for both component ITU-R BT.601 and composite digital video and four groups each of four channels of embedded digital audio. Most broadcast digital equipment includes SDI which greatly simplifies its installation and signal distribution. It can transmit the signal over 200 meters (depending on cable type). HD-SDI Standardized in SMPTE 292M, this for 4:2:2 HD television. The serial bit- stream runs at 1.485 Gb/s to carry up to 10-bit Y,Cr,Cb component video as well as embedded audio and ancillary data. The interface is also specified for fiber for distances up to 2 km. 3G SDI (SMPTE 424M) operates at 2.97 Gb/s, twice the clock rate HD-SDI and is designed to carry high bandwidth HD television such as 1080/50P, 1080/60P, HD RGB, as well as 2K DI images. See also: Dual link, HSDL, Embedded audio