Published: TV Technology Magazine

Issue:  29 June 1998





A Bitstream Controversy Continues   

The Debate over Bitstream Speeds has only Intensified with the Onset of DTV 



by Joe Fedele



WASHINGTON

  As stations begin their migration to digital, an increasing number are looking at the data rate handling 

capabilities of equipment they purchase. A number of controversies - and incompatibility problems - have 

surfaced over the past decade as equipment manufacturers jockey for position, trying to corner a slice of the 

market.

  About eight years ago, Panasonic Broadcast and Grass Valley (now part of the Tektronix group) 

discovered that the 13.5 MHz sampling rate (which yields a 270 Mbps bitstream) was not fast enough for 

16:9 video and would impair its horizontal resolution to unacceptable levels.

  Hence, 18 MHz sampling, which delivers a 360 Mbps bitstream, was developed and incorporated into the 

SMPTE 267M sampling and SMPTE 259M-D serial transmission standards. The new standards fostered 

the development of equipment that was capable of much faster data rates than had been previously been 

considered necessary. 



DISAGREEMENTS CONTINUE

  But the controversy didn't end there; in fact, it has intensified with the introduction of DTV. A number of 

broadcast groups and manufacturers believe that broadcast facilities should be outfitted to allow for 

bitstreams of up to 1.5 Gbps. This, they say, would provide for the distribution of uncompressed HDTV 

(1080i or less) programming throughout a facility.

  But the cost of such an installation drove manufacturers to develop something in between. Consequently, 

the term mezzanine level was entered into the television engineer's vocabulary. Mezzanine level distribution 

has been referred to as "lightly compressed HDTV."

  Now the question lingers: What should that mezzanine level be? Peter Lude, vice president of automation 

and transmission systems for the Sony Electronics Business & Professional Group, believes broadcasters 

should utilize what works for them now and seek upgrade paths in the future. 

  "Sony has 270 [Mbps-capable] equipment now and will introduce 360 [Mbps equipment] if the market 

demands it," he said. But, he added, "there hasn't been a large market for it yet." 

  In the end, Lude said, a number of bit-rates will be needed. "My opinion is that broadcasters will support 

different formats based on business decisions [that include] factors [such as] their competitors' capabilities. 

We want to support as many standards as possible."

  Tektronix appears to be in agreement with the concept of multiple bit-rate facilities. The company released 

three new Grass Valley HDTV products at NAB '98 that are based on existing platforms. Tektronix says 

that its new family of HDTV routers and switchers offers familiar formats and compatibility with current 

Grass Valley systems.   

  The Tektronix approach for distributing HDTV within a facility is to give broadcasters an option: Allow 

them to reuse their existing infrastructure of both 270 Mbps and 360 Mbps component digital routing. 

  Sony is setting its sights a bit higher. "We think that broadcasters should be focusing on 540 Mbps instead 

of 360,"Lude said. "Sony feels strongly and recommends that 4:4:2, 10-bit video, which translates into 540 

Mbps, be maintained throughout the plant." 

  Will the development of 540 Mbps equipment significantly increase the cost of equipment as some fear? 

Not so, said Lude. "The CMOS semiconductors used in most of this equipment can handle up to 540 Mbps 

without any problems. There really is no cost difference between manufacturing 270 and 540."

  How all this will be resolved is still unclear. One problem, industry experts have said, is that 

manufacturers are assuming that a reasonable infrastructure already exists in most of the nation's broadcast 

facilities. A suggested router upgrade or a mention of compatibility with existing equipment is based on the 

notion that component digital routing is the norm. This is not the case in a number of medium- to small-

market stations. Those issues, among others, are yet to be resolved. n



  Joe Fedele is president of Fedele & Associates, a technical consulting firm based in Miami. He can be 

reached at jfedele@fedele.com or at www.fedele.com.

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