Time Warner Cable
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.
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.
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.)
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.