HDMI sounds off over DVI

New DTV set interface broadens DVI to include eight audio channels across one slim wire

A new digital interface for DTV sets and related devices was introduced last week by a consortium of consumer-electronics manufacturers and Hollywood studios that believe it's a step toward securing digitally distributed TV content.

Called HDMI (the acronym stands for High Definition Multimedia Interface), the technology is based on the already existing Digital Visual Interface (DVI), which was designed by chip maker Silicon Image to transmit uncompressed digital video images to flat-panel PC monitors. The HDMI interface adds eight channels of audio to the interface, meaning that DTV sets and related devices could send both video and audio signals through one connection.

The consortium comprises CE makers Hitachi, Matsushita, Philips, Sony, Thomson and Toshiba, Hollywood studios Fox and Universal, plus DirecTV, EchoStar and Silicon Image. Intel is also involved, providing high-bandwidth digital content protection (HDCP) security for the HDMI.

"The industry would prefer to solve its own problems, and this is one example of that," says Steve Tirado, COO of Silicon Image, the chip manufacturer that spearheaded the effort.

"It advances the ball into the move to a digital era," says Peter Fannon, Panasonic director, government and public affairs. "This moves the DVI towards being a smaller, typical consumer-sized wire and away from the big plug that is used to connect PCs to independent monitors."

To date, digital connectivity between devices has been limited to FireWire, which passes compressed video and audio signals from one device to another. But because it sends compressed signals, it also allows for recording of signals—something that makes the piracy-sensitive studios nervous. Because HDMI uncompresses those signals, they are too large to record and, thus, are something Hollywood may endorse.

"This interface will join 1394 as one of two ways to send a copy-protected digital signal from a set-top device to a digital display," says Dave Arland, Thomson spokesman. "And this will basically make the last jump from the set-top box to the television."

Arland adds that because the uncompressed signal makes it difficult to record today, Hollywood finds it attractive.

Prototypes of the technology are expected to be seen at CES next year, although Arland says it may be found on set-top boxes as early as this summer. Its 5GBbps of bandwidth can handle all ATSC HDTV standards and supports eight channels of audio. The uncompressed HDTV signal takes up 2.2 Gbps, according to Tirado.

One of the benefits of HDMI, according to the consortium, is that it is backwards-compatible with DVI interfaces (which can be found today on select DTV sets). But that compatibility isn't perfect—at least not today. Current DVI connections do not include audio, but HDMI will. Arland says that consumers who use the DVI connection for video input today will need to pass audio signals the way they currently do, with a forest of cables behind the TV.

"There is a large installed base of consumers who won't be able to take advantage of DVI, HDMI or even FireWire in most cases," adds Arland, who with others involved concedes HDMI is not the perfect solution. But, used with FireWire, it appears to be a more complete solution, although that may disenfranchise current DTV set owners if the industries aren't careful.

"There is some discussion that needs to be added about grandfathering and making sure we aren't stranding the very people who have made an investment to make this possible," says Arland. "And there's a fairness issue in that everyone shouldn't jump over to HDMI and abandon FireWire, because then you can't do recording."

HDMI could help concerned DTV owners readily focus their energies if they're concerned.

"If someone is worried about digital interfaces, they should call Jack Valenti," says Arland. "A fact of the transition is that Hollywood is requiring digital interfaces that are copy-protected."