Published: TV Technology magazine

Issue: 20 April 98



5.1 Audio Channels — The Final Frontier?





by Joe Fedele



MIAMI

  An old radio engineer joke goes like this. Question: How does a radio engineer test an audio circuit? Answer: With 

lots of test gear and time. Question: And how does a television engineer test an audio circuit? Answer: “Hello, can you 

hear me?”

  Until the introduction of TV stereo, consumers typically listened to their television’s audio on a 2-inch speaker that 

had slightly more dynamic range than the proverbial cup and a string. 

  Those days have rapidly diminished as consumers began to install home theaters with Dolby Surround Sound. The 

subsequent introduction of the Dolby AC-3 digital audio standard and its inclusion into the DTV standard may very 

well become “the final frontier” for most broadcasters as they begin to evaluate the cost of accommodating the addi-

tional four channels of audio (true AC-3 production requires six channels) into their stereo plants.

  The AC-3 standard, also known as “Dolby-D” by Dolby Laboratories, its developer and patent holder, utilizes what is 

typically called 5.1 audio channels. These channels are often referred to as the left, right, center, right surround, left 

surround and a bass effects channel (the .1 part).

  Ironically, while most broadcasters have been worried about the difficulties involved in multiple video streams, few 

have taken the time to analyze the cost and complexities of producing 5.1 audio channels and its associated metadata 

(see Defining the Issues — What is Dolby Metadata?, on page TK).  But it’s a reality that broadcasters and production 

houses alike must address.

  “There is not much of a call for 5.1 audio yet, but I’m banking on 100 percent [interest] in the future,”  said Marcelo 

Gandola, senior audio engineer for Broadcast Video Inc., a Miami-based production house. “5.1 is still cutting-edge 

technology for most advertisers, but once they hear it, their response is ‘Wow, I never heard audio like that before.’”

  Gandola added that the complexities of mixing 5.1 audio make it a true challenge for most accomplished engineers, 

let alone the novice. “Broadcasters are still familiarizing themselves with 5.1; it’s still a baby.” 

  And, like a growing child, AC-3 will be a dollar-intensive proposition. And the cost of implementing 5.1 audio can 

add up very quickly.



AUDIO OVERHAUL

  Audio production rooms must be overhauled to handle the production of the six audio channels. And since VTRs are 

only capable of handling a maximum of four audio channels, some outboard means of recording will have to be in 

place.

  The difficulties and cost of some editing will also rise dramatically. Edit time will be greatly increase (as will your 

operational budgets) as advertisers begin to develop new and innovative ways to catch viewers’ attention and keep 

them from escaping to the fridge during commercial breaks.

  According to Paul Berger, director of technology for the CBS Engineering division,  monitoring audio will become a 

major issue in 5.1 plants. “There is no possible way to properly monitor 5.1 audio around a plant,” he said. “How do 

you monitor 5.1 in a noisy equipment room? At least with stereo you could put on a set of headphones.”

  QC stations (used for monitoring program quality) will require significant improvements, such as having five full-

range speakers and a complementary subwoofer.  After adding one amplifier for each monitor, the cost of a good QC 

station can soar into the thousands if properly designed.

  The good news is that Dolby Labs has made the distribution part of AC-3 relatively simple by providing an encoder 

(model DP567) capable of delivering the AC-3 signal through a plant and to the viewers. Broadcast facilities that op-

erate two-channel analog audio systems can incorporate the encoder without any other modifications to the plant.

  The catch is that this scenario will only deliver a simplified form of Surround Sound that does not include the inde-

pendent surround features and low-frequency effects channel. Dolby Labs calls this approach a “near-term solution.”

  In order to implement the full-blown version, stations will have to employ Dolby’s newest technology, which the 

company calls “Dolby-E.” Dolby-E is a new coding technology designed specifically for distribution applications that 

will allow much of the existing two-channel linear PCM digital audio infrastructure, such as VTRs, routers and em-

bedders, to carry multichannel audio. 

  But Dolby-E requires the use of an AES-type digital audio distribution system with at least two channel pairs (four 

PCM audio channels). When combined with the newly released Dolby-E coding system, the two PCM pairs will be 

capable of providing up to 16 audio channels. 

  Dolby Labs designed its Dolby-E system to mimic a two-channel 20-bit (or 16-bit) 48kHz PCM audio signal that can 

carry up to eight discrete audio channels. Because Dolby-E encoders will only work with AES/EBU digital audio pairs 

any analog systems must be replaced. (see sidebar for a description of AES/EBU audio)

  Berger sees the Dolby-E technology as a very promising solution for stations in the future. But, he said, “what do we 

do in the mean time?”  

  As of this writing, the Dolby-E standard had just been announced but equipment was not available for shipment. 

  Some industry analysts believe production houses will likely feel the greatest pressure to produce 5.1 programming. 

Gondola said that “it’s just too early to tell” how quickly the demand for 5.1 audio will take before broadcasters are 

pressured into diving it.

  The implementation of 5.1 audio “is probably one of the softest areas of DTV,” according to Berger. “Remember, 

you have to mix the audio, manage the data, switch it, monitor it and handle the metadata,” he said.  “And even if you 

get it you can’t process it.” 

  In the next few years consumers will begin to invest heavily in DTV systems with elaborate home theaters. Many be-

lieve it is only a matter of time before consumers begin to demand 5.1 quality. And, just as AM listeners flocked to 

buy FM radios for the improved quality with stereo sound, consumers expect more for their money in the TV audio 

arena. Now they are starting to know what to listen for. n



  Editor’s note: Dolby Laboratories maintains an extensive listing of audio related guides and papers on its Internet 

Web site at www.dolby.com/tech.

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