DTV Audio Update 

From Dolby Laboratories | September 2008 | Vol. 9 No. 3

Broadcasts of the Olympic Games in HD and Dolby® Digital 5.1 increased dramatically worldwide this year, and Dolby provided both products and personnel to assist broadcasters in delivering a premium experience to viewers.

For the first time, the host broadcaster, Beijing Olympic Broadcasting (BOB), made available both high-definition video and 5.1-channel discrete audio from every venue. China Central TV (CCTV) delivered the 29th Summer Games to the host country with exhilarating high-definition picture and Dolby Digital 5.1 from its new Beijing headquarters via its new free HD channel, which launched at the beginning of 2008.

All audio for the games was embedded within HD-SDI streams, with stereo in channels 1 and 2 and discrete 5.1 audio in channels 3 through 8. Audio and video signals were distributed from Beijing’s International Broadcast Center (IBC) to the CCTV HD studio, where local commentaries were added. The mixed 5.1 audio was fed into a Dolby DP571 Dolby E encoder and then reembedded along with the mixed stereo feed back into HD-SDI. In the CCTV transmission center, the 5.1 Dolby E audio was decoded, then reencoded into Dolby Digital for transmission to viewers.

CCTV also used Dolby’s DP570 Multichannel Audio Tool to set metadata parameters and emulate downmix results for confidence monitoring. A Dolby LM100 Broadcast Loudness Meter was connected to the system to monitor loudness levels and offer mixers a reference for adjustment of commentary audio levels. Dolby engineers were on-site to offer comprehensive technical support to CCTV, aiding in program mixing, quality control, and final transmission. 

Comprehensive Coverage of Games Throughout Europe and the US

NBC broadcast the games in HD with Dolby Digital 5.1 on its NBC HD channels in the US. NBC also employed Dolby LM100 Broadcast Loudness Meters, and successfully used them to consistently mix to a dialogue reference level of –23, matching its other network content. In addition, the LM100s were used at the major Olympic sports venues to measure loudness, ensuring the best and most consistent loudness experience for viewers.

High-definition transmission with multichannel audio has increased drastically this year, and viewers throughout Europe were able to watch the Summer Games in style. EBU multilateral and unilateral HD contribution feeds were used by most of the European broadcasters to receive the signals from Beijing. For the multilateral feeds, the 5.1 audio was encoded in Dolby E.

The BBC, for example, broadcast throughout the UK in HD and Dolby Digital 5.1 audio on Sky HD as well as the new FreeSat HD platform. In Spain, the new TVE HD channel provided coverage in Dolby Digital 5.1 via Sogecable, the nation’s leading pay-TV platform. TVE distributed the audio as Dolby E streams to Sogecable prior to transmission in Dolby Digital. RTP Portugal launched a new HD channel with Dolby Digital 5.1 for the Beijing Olympic Games that is carried on the ZON cable TV platform.

Sweden’s SVT also broadcast the games via satellite, cable, and terrestrial systems. The network brought multiple HD contribution feeds from Beijing back to Sweden complete with 5.1 audio via a dedicated dark fiber link, joining other European public broadcasters such as ORF (Austria), HD Suisse (Switzerland), and TVP (Poland) that also offer coverage in HD complete with Dolby Digital 5.1 audio.

Finally, Slovenian broadcaster RTS transmitted SD services only in stereo via DVB-T, and its HD test transmitter (also DVB-T) broadcast MPEG-4 (H.264) video with Dolby Digital 5.1 audio. The network received its signals via an EBU network, adding commentary and graphics where appropriate. 

France Prepares for HDTV Uptake

French broadcasters are preparing for a significant upturn in their potential HD audiences. Beginning in December 2008, all HD receivers sold in France must include an MPEG-4 HD tuner (rather than the SD tuner that is currently mandated).

Given the success of 5.1 audio services on existing French SD TV services, it’s no surprise that the French HD receiver standard includes comprehensive support for next-generation multichannel audio. The specification requires all receivers to support Dolby® Digital Plus audio and also (from late 2009) multichannel HE-AAC audio.

Following its acquisition of Coding Technologies, the original contributors to the HE-AAC standard, in November last year, Dolby has been assisting France’s terrestrial operator TDF with testing of both Dolby Digital Plus and HE-AAC audio. A suite of dedicated test streams have been created to assist manufacturers in building receivers that are fully compatible with the French specification.

Dolby Digital Plus and HE-AAC decoding have also been specified by other European HD groups, including the Spanish HD Forum and NorDig. Dolby is currently developing dual-decoding solutions that will simplify the inclusion of both formats in European receivers, which will extend the use of HE-AAC in a broadcast environment.

Dolby at the IBC Exhibition

Those involved in the creation, management, and delivery of content for the entertainment industry will head to Amsterdam this month for the IBC2008 exhibition. At booth B28 in Hall 2 of the RAI Center, we’ll be showcasing how years of end-to-end broadcast experience make Dolby an essential partner across the entire content creation and delivery process. From traditional broadcast technologies to new innovations for optimizing content delivery over HDTV, IPTV, digital radio, mobile services, and beyond, the industry can rely on Dolby to be there every step of the way helping make good entertainment technologies great.

This year at IBC, we will be displaying our product and technology solutions for next-generation broadcast services, consumer broadcast products, and bandwidth-constrained future delivery methods. Included will be new functionality for the increasingly popular Dolby® DP600 Program Optimizer. We’ll also introduce Dolby Media Meter loudness metering software to the European market. Finally, we will highlight the many Dolby partner products and implementations using Dolby technologies, from such companies as Cisco, Digidesign, Harmonic, Omneon, Pace, Sagem, Tandberg, Telestream, Thomson, and many others.

Be sure to visit us at the IBC Exhibition to see how we can enhance your content today—and tomorrow.

Time Warner DP600 Program Optimizer Case Study

Time Warner Cable Media Sales Case Study
Managing Network and Commercial Loudness via Audio Metadata 

Time Warner Cable, the second-largest cable operator in the US, currently serves more than 8.5 million digital video subscribers and provides an enormous amount of programming to its customers. As the cable industry continues to evolve, and new digital tools become available on a daily basis, companies such as Time Warner Cable are becoming aware of a need to refine the way in which they ingest audio content. To this end, the cable giant recently completed a study concentrating on how to best maintain consistency of audio levels across programming, commercials, local ad spots, and other inserted content.

Time Warner Cable Media Sales’ Southwest Region Operations Center teamed with Dolby in conducting a test focused on its ingestion of digital content. This particular Operations Center, with Master Control/I.T. regionally managed by Ivan Larsen and Engineering regionally managed by Ron Moore, supports more than 230 insertion servers, with five cable multiple system operator (MSO) partners. It also maintains more than 25 physical insertion locations, ingests approximately 1,000 pieces of content weekly, and inserts and monitors content on more than 2,450 channels. It manages designated market areas (DMAs) in Texas, Kansas, Colorado, and Nebraska, which comprised the testing region.

The study targeted digital program ad insertion applications (on Time Warner Cable’s digital tier of services), which total more than a quarter million ad inserts daily. The study focused on the proper use of dialogue normalization to improve subscriber experience, and both real-time and non-real-time (file-based) system components were considered. First, the provisioning practices of local (head-end) digital simulcast encoders was investigated by analyzing content over which local control was possible (via the dialogue normalization value and incoming loudness levels with baseband signals). Also considered were loudness levels of pass-through services (for which local control is not possible).

A Snapshot of Ingest Content
In the Time Warner Cable study, 18,695 commercial ad spot files were analyzed, and among these files (all of which were stereo audio), 500,000 data points were collected. The file-based ad spot content used MPEG-1 LII audio almost exclusively at the acquisition point. Unlike Dolby® Digital content, MPEG-1 LII does not contain audio metadata (and therefore does not contain a dialogue normalization metadata parameter that the decoder can utilize to maintain consistent loudness levels among programs, ad spots, and so on).

Due to the lack of dialogue normalization metadata (in the MPEG-2 LII audio PID), Time Warner Cable’s ad spots had previously been transcoded in a “blind” fashion, using a commercially available transcoder with a default set of Dolby Digital metadata settings. Specifically, all ad spots were transcoded utilizing a “static” value, or the transcoders default dialnorm value, prior to final QA.

Steps to Improve Subscriber Experience
Time Warner Cable found that blind file-based transcoding with a static (default) dialogue normalization value leads to unnecessary level shifts away from the Dolby Digital decoder reference level (in the set-top box or A/V receiver). Its Master Control Center utilized a Dolby DP600 Program Optimizer to analyze and subsequently nondestructively correct the success rate of blind transcoding, using the DP600’s adaptive and automated speech-based ITU-R BS.1770 measurement method.

The analyzed (and subsequently corrected) ad spots were divided into two groups for analysis: Group I contained locally produced content, primarily ingested via FTP directly from ad agencies. Group II comprised ad spots delivered via a popular ad content aggregator.

For group I, only 34 percent of material had correct dialogue normalization (after the blind transcode); group II did not fare nearly as well, with only 6.7 percent success. In both groups, the incorrectly set values were dispersed over a fairly wide range. Group II fared even worse in this regard; while the majority of content was spread over a smaller loudness range, that distribution of individual loudness values was centered at approximately 3 dB above the correct dialogue normalization value. See figures 1 and 2 for more detail. Note that the red areas in the figures indicate spots that would fall outside the listener's comfort zone after the blind transcode.

Figure 1

Figure 2

Subsequently, the automated analysis and correction engine on the DP600 was used to correct the dialogue normalization value within each of the ad spots. (See figure 3.) This process does not require a decode/reencode cycle—that is, this unique process does not impact program dynamics. It also in corrects the dialogue normalization value in faster than real time. The difference between blind-transcoded files and files corrected using the DP600 was dramatic. For corrected files, the loudness was much more in balance with the surrounding programs. An example comparison of corrected and uncorrected ad spot audio levels as they relate to the surrounding program audio loudness can be seen in figures 4 and 5.

Figure 3

Figure 4

Figure 5

Lastly, the study also required Time Warner Cable to ensure that the dialogue normalization value on every digital simulcast encoder was correctly provisioned. The correct dialogue normalization value for each digital simulcast service was derived via long-term dialogue measurements using a Dolby LM100 Broadcast Loudness Meter. (See figure 6.)

Figure 6

Checklist for Success
Overall, this study provides a practical blueprint applicable to many broadcasters wishing for consistent, repeatable, and predictable results during the quality-control process. It also helps ensure proper setting of the dialogue normalization parameter for every piece of content. Time Warner Cable found that by incorporating minor work-flow adjustments utilizing the DP600, it could ensure that the dialogue normalization value always agrees with speech loudness of each ad automatically using the DP600. The company was also able to ensure that each digital simulcast encoder utilizes a proper dialogue normalization value by utilizing the LM100.

Furthermore, by analyzing the level of material on digital pass-through services and sharing that data with networks, Time Warner Cable could alert the networks to ongoing loudness issues and work toward correcting loudness levels when local control is not an option. Throughout the industry, many networks/programmers have responded to such advice from cable operators, adapting accordingly with corrective changes to their subsequent output. Overall, these efforts have made a great impact in the United States.

There is an increasing amount of documentation supporting proper use of Dolby Digital metadata and dialogue normalization as a means to improve subscriber satisfaction. Loudness issues that have hampered the consistency of cable broadcast audio can be easily addressed if the industry moves forward together with the proper use of dialogue normalization (or by a local decode/reencode stage at the head-end). If content providers, postproduction houses, and manufacturers throughout the industry continue to work with networks and programmers, together we can ensure proper provisioning of dialogue normalization, consistent levels for all programming, reduced complaints, and better viewing for all.

Find additional information on the Dolby DP600 Program Optimizer for file-based environments.

Guidelines for Dolby E with 50/60p Frame Rates

In most parts of the world, the initial uptake of high-definition (HD) broadcasting involves interlaced video formats. As many European broadcasters and their equipment suppliers are already experienced in handling Dolby® E surround audio in interlaced SD systems, good practices can easily be transferred to HD. Considerations for carriage of Dolby in interlaced HD systems are similar to those for SD, as frame lengths are equal (see figure below).

For 50/60i (at either 25 or 29.97 fps), there is one Dolby E frame that starts on the odd-numbered field, and crosses over and ends in the subsequent even-numbered field. This does not normally cause a problem because equipment switches at the SMPTE RP168 switch area based on the first odd video field, where the correctly aligned Dolby E guard band is located. Embedders, deembedders, frame synchronizers, and switchers work fine in this mode, and the Dolby E stream remains error free.

With the increasing popularity of progressive HD video formats, we must ensure that no problems occur with video frame lengths that are half the duration of interlaced video frame lengths. In this mode, the guard band of Dolby E (which protects against error during a switch point) does not cover all SMPTE RP168 switch areas—only every other switch area. If appropriate precautions are not taken, a video switch point has a 50 percent chance of corrupting one Dolby E frame (see figure).

Where Dolby E is used in 50/60p environments, Dolby E frames have a length of two video frames (40 or 33.3667 ms), because the Dolby E frames are still being generated at 25 or 29.97 fps. As with the interlaced video example, in progressive video the Dolby E frame starts on one video frame and crosses into the next frame, where it then ends. As current 50/60p equipment doesn’t always switch on the first frame (it may switch on the second frame), a single frame of Dolby E may be corrupted at this switch point. This typically results in a momentary (one frame) mute in suitably designed broadcast systems, which is considered acceptable (although not ideal) by several existing broadcast users. It should be noted that HD-SDI embedders and deembedders work fine in this mode; only switching and frame synchronizing cause an issue. 

Dolby is currently working on a document for manufacturers of 50/60p-capable equipment that will provide guidelines for further improved solutions. These approaches are being verified with various broadcast equipment manufacturers to ensure their practicality. Dolby has detailed further information on how to implement Dolby E carriage and switching; this information may be obtained by equipment manufacturers with the signing of an NDA. Visit our booth at IBC and ask for more information.

Learn more about Dolby E for broadcast distribution.

New UK Ad Loudness Regulation

 

The Broadcast Committee of Advertising Practice, part of Britain’s Advertising Standards Authority (ASA), recently issued a regulation referencing proper sound levels in advertisements. The regulation advises engineers to employ a loudness meter during ad content creation, preferably one conforming to the ITU-R BS-1770/1771 standard. It goes on to state that if a loudness meter is not available, engineers must ensure that the peak level of this material be no higher than 6 dB below the peak level of the surrounding program material. In the UK, program material peaks at +8 dBu, so ads must not peak at levels higher than +2 dBu.

While ITU-R meters can be useful in helping mixers maintain the proper +2 dBu peak level, a product such as the Dolby® LM100 Broadcast Loudness Meter provides all the features necessary to help engineers preparing ad content to fully adhere to this regulation, and to ensure that loudness is consistent among various advertisements. Alternatively, those who work in file-based environments can use the DP600 Program Optimizer to estimate and correct the loudness of their program material or correct metadata to a measured level.

Though this regulation applies only to advertisements, it should also help to level out loudness in buffer material, too, because advertisers will no doubt be vigilant about buffer material that is subjectively louder than their ads.

Find more information on Dolby’s complete line of broadcast loudness solutions.

Dolby at the 2008 AES Convention

At the 125th AES Convention, to be held October 3–5 at the Moscone Center in San Francisco, Dolby will be exhibiting in booth 808. Dolby offers products and solutions for audio production, postproduction, and broadcast that help make your job easier and your results better. We invite you to visit our booth, where we will highlight the Dolby® DP600 Program Optimizer and our complete Dolby Media Producer product line. Dolby is proudly sponsoring the second annual AES Broadcast Conference, which is also taking place during the AES Convention. View the AES Broadcast Conference program for additional information.