Silicon Image chips add audio support to DVI link

Silicon Image chips add audio support to DVI link
SAN MATEO, Calif. — Silicon Image has developed a new version of the Digital Visual Interface that includes support for audio for the first time. Though not yet accepted as the next spin of the DVI standard, the work is stirring the ongoing debate over which digital interface, DVI or IEEE 1394, will become the mainstay for consumer electronics systems such as set-top boxes.

DVI is seen as the best way to carry uncompressed high-definition pictures to a high-resolution display, but it is a unidirectional, point-to-point technology. Silicon Image's new PanelLink A/V technology, which the company has implemented in a pair of transmitter and receiver chips, is designed "as a single, universal point-to-point connector," said Joseph Lee, manager of product marketing at the Sunnyvale, Calif., company.

By contrast, designers said 1394 is best-suited for recording and bidirectional networking of compressed signals — a must as consumer vendors add Internet connectivity to their boxes.

OEMs are facing pressure from content owners and service providers to adopt DVI, a move that could force them to implement both interfaces to meet varying needs. That's something system makers are disinclined to do for cost reasons. However, "If service providers spec DVI in, it'll be a done deal. We'd have to bend," said Frank Romeo, director of the digital-TV strategy group for Samsung Electronics Corp.

The lack of audio support has been one sticking point standing in the way of DVI's broad acceptance. By devising a technology that supports embedded digital audio data within the existing DVI electrical and physical layer, Silicon Image is hoping to position PanelLink A/V as the only interface choice with enough bandwidth — up to 5 Gbits/second for a single DVI link — to accommodate uncompressed digital data such as high-definition video.

"Consumer electronics manufacturers can now use PanelLink A/V to transmit more channels of surround sound, or a high-end audio-coding format such as Meridian Lossless Packing," Lee said. MLP sampling rates are too high to be handled by the conventional Sony/Philips Digital Interface (S/PDIF), which maxes out at 3 Mbits/s. "Innovations of high-quality digital audio technology no longer need to be constrained by the S/PDIF's bandwidth capacity," said Lee.

In PanelLink A/V, digital audio signals are "embedded and modulated into the DVI clock signal" and can be "accurately extracted" after they have gone through the DVI link, Lee explained.

With its track record of providing an underlying technology for the current DVI spec, Silicon Image is confident the PanelLink A/V proposal will win the nod from the Digital Display Working Group (DDWG), which published the DVI 1.0 spec. This open industry group is led by Intel, Compaq, Fujitsu, Hewlett-Packard, IBM, NEC and Silicon Image.

Mark Waring, technology initiative manager at Intel Corp., who also serves as DDWG's secretary, noted that the inclusion of audio was "one requirement we'd have to meet in order to get the consumer electronics manufacturers' acceptance" for DVI.

Audio options

He cautioned, however, that PanelLink A/V is not the only technology being proposed for that job. "There are several different ways to add audio to the DVI," Waring said, and they are being privately discussed among various companies.

On Intel's part, Waring said, "There is no official endorsement or plan to incorporate Silicon Image's new technology at this point." However, he added, "We're certainly interested in taking a closer look at what they Silicon Image have done. We will be discussing this over the next couple of months."

Meanwhile, Silicon Image plans to move forward with production of its PanelLink A/V transmitter and receiver chips, using a 0.35-micron process at Taiwan Semiconductor Manufacturing Co. Chips are scheduled for sampling in the second quarter, with volume production beginning in the third.

Lee promised that the new chips will be priced roughly the same as the current-generation DVI devices. A DVI transmitter chip costs less than $5, while a receiver IC sells for less than $12, he added.

Stubborn debate

Although companies such as Echostar, JVC and Scientific-Atlanta showed off DVI-equipped set-top boxes, D-VHS systems and projection TVs at this month's Consumer Electronics Show, the DVI vs. 1394 debate lingers stubbornly. The choice of a digital interface is still a hot issue among many consumer manufacturers, as is the possibility they might have to incorporate both.

"My first reaction to the original DVI was, 'you guys do only video? You mean, you are asking us to go backwards?' " said Romeo at Samsung. Noting that IEEE 1394 supports not only audio and video, but also command and control signals over a single cable, Romeo said that even if PanelLink A/V adds audio to the mix, DVI will still be lacking the control element.

And for companies such as Samsung, which are planning to implement Internet Protocols over IEEE 1394 for home networking applications, "The fact that you can't do IP over DVI is a real problem," Romeo added.

Tommy Poon, executive vice president and director of the Murray Hill Lab at Mitsubishi Electric Research Laboratories, agreed. "We're focused on how to get networked data into a TV set," he said. "The IEEE 1394 is far more network friendly for that application."

"To be at all viable, DVI needed audio, but I don't think that the addition of audio will change DVI's role," said Scott Smyers, vice president of Sony's Interconnect Architecture Lab. In Symers' view, DVI is still "not usable in moving the bits around the home and in recording the bits in storage devices."

DVI is essentially a point-to-point digital interface from a single source to a display. To hook more than one digital consumer device to a TV, the TV must pack extra DVI interfaces — one per connected device. Further, every time a user changes the entertainment source, connected devices must be switched.

Meanwhile, the 1394 interface allows devices like set-tops, personal video recorders and DVD players to be instantly connected to everything, thus forming a "network," with no switching needed.

Although Samsung's computer monitor division is already embracing DVI, Romeo said that his group is still carefully studying whether just one digital interface will do or if Samsung set-tops must feature both.

Protected content

Indeed, some Hollywood studios and other content owners and service providers are increasingly vocal in their support for DVI — in large part for its content-protection technology. The fact that DVI does not allow any recording at all is one reason it is drawing support from content owners, industry sources said. Another is the fact that the sheer volume of uncompressed signals DVI deals with makes it inherently less vulnerable to theft and illegal copying.

Echostar, which was still studying the issue six months ago, has now come out in support of DVI. A spokeswoman said DirecTV is "exploring the issue, but no decisions have been made." Similarly, CableLabs, the R&D arm for U.S. cable operators, said this past week it is still examining whether to specify DVI as an enhancement for the OpenCable spec.

But in the Hollywood community, the content-protection bugaboo appears to be swinging opinion toward DVI, thanks to its High-bandwidth Digital Content Protection (HDCP) technology. The analogous scheme for 1394, called Digital Transmission Content Protection (DTCP), is being nitpicked by some studios for allegedly not providing tight enough security.

"We prefer, in general, a protected digital connection over an unprotected analog interface," said Andrew Setos, senior vice president of broadcast operations and engineering at Fox Television. "We are encouraging companies like DirecTV and JVC to gradually phase out an analog interface" from their set-tops and other digital consumer systems.

Digital delivery to projectors and displays "can avoid problems of ghosting and image degradation caused by analog connections," concurred Jerry Pierce, senior vice president of technology at Universal Studios. He added, "It appears that DVI is a good solution to this. We also like the DVI/HDCP connection, as it provides a secure connection to displays."

Like Pierce, Setos also indicated that he considers the combo of DVI with HDCP as a solution likely to appeal to the studios. Yet Setos sees a role for 1394 as well. "DVI is good for viewing digital content on a high-resolution display, but it's not for recording information," he said. "Meanwhile, 1394 is good for moving compressed signals around the home." Thus, Setos said, "1394 and DVI are completely complementary."

Who's got control?

As for 1394's DTCP copy protection scheme, Setos said, "that is a subject of ongoing negotiations" between content owners and developers, mainly centering on the issue of so-called "encoding rules." The crux of the matter boils down to who keeps control — or, more accurately, who gets to decide how copyrighted content should be protected — as it traverses from analog to digital, broadcast to storage, DVD to Internet.

For studio executives looking to exert control over their copyrighted content even after it's arrived in a consumer's storage device, DTCP does not fit the bill. The technology allows only three options, "copy once," "copy never" and "copy freely." Some studios want what they call "extended copy-control information" that can specify and control, for example, how long consumers can keep content after it is delivered and stored.

Although not all the studios concur, some see DVI as an easier way out, at least for now.

For its part, the 1394 Trade Association views DVI as a solution only for short-term and niche applications. James Snider, the association's chairman, said that "1394's role is to enable many different devices to share high-definition video, audio, IP traffic and other information for display and recording devices and for information appliances."

By contrast, he said, "DVI is limited to a single-point solution between a computing device and a display. It's a good technology for that niche."

The debate leaves consumer electronics manufacturers mulling the possibility of using both interfaces in at least some products.

Mitsubishi's Poon, for example, predicted that high-end DVD players might incorporate both 1394 and DVI, the latter primarily to give consumers the option of connecting their DVD system with a high-resolution flat-panel display.

But an average, low-cost DVD player will probably have 1394 alone, said Poon, "because we believe that 1394 will be more economical and good for high-level connectivity." From a marketing standpoint, "We want to make sure that our products can get connected to as many other products as possible."