Dennis Ciapura /
06.01.2013
Originally featured on BroadcastEngineering.com
STBs and CALM - FULL ARTICLE
Can cable and satellite set-top boxes undo CALM compliance?

Nielsen reports that 103 million of 114 million TV households (90.3 percent) get their service from one of the Multi-video Program Distributors (MVPDs).

While TV broadcasters have been keenly attentive to the ramifications of the CALM Act from the broadcast perspective, the MVPD role has been viewed mainly as cable and satellite turf. The operative notion is that if MVPDs incorporate ATSC A/85 recommendations within their plants, they will present a transparent pass-through for broadcast CALM compliant programming. What at first seemed like a nearly impossible task, given the hundreds of program sources they handle, was made simpler by the source certification concept the FCC is pushing. Program providers would certify their A/85 compliance, and MVPDs would enjoy a safe harbor pass as long as they didn’t alter the audio and there are no viewer complaints. This assumed compliance mode is clearly a godsend for MVPDs.

Is it really that good?

So it would seem that all loudness things are well in our world. But are they? The last element in the MVPD chain to the viewer is usually the ubiquitous set-top box. These take many and varied forms, but most of them feature some kind of audio gain control option as one of their setup features. After years of fielding complaints about varying audio levels, most MVPDs provide the boxes with the compression on. When customers complain about program or commercial loudness peaks, their customer service representative routinely instructs them to make sure the dynamic range compression is on. This always made a lot of sense … before CALM.

The obvious questions are: Can TB audio compression undo A/85 level corrections, and, if so, how prevalent is the problem? As to the first case, if the form of leveling is simple gain reduction with a threshold below normal program levels, it would certainly level out any element-to-element level corrections per A/85. For example, a commercial element that exhibited an LKFS well above anchor dialog and was reduced would be expanded back up to full program level. This is the form of STB leveling that was prevalent for years as significant channel-to-channel level variations were common and this leveling mode minimized that problem.

An enlightened approach

Fortunately, many newer STBs embody a more enlightened approach. For example, the Dynamic Range Compression feature of the latest model of Motorola STB has its threshold above normal program levels and reduces the peak program levels by about 5dB to 10dB, even when set for heavy compression. This form of compression should not affect A/85 levels because it comes into play well above anchor level. It is intended to limit the maximum loudness level produced in loud scenes for viewers whose personal taste or living environment make full dynamic range undesirable. This is more often the case with movies on cable and satellite. The practical broadcast TV maximum program level overhead these days seems to be limited to about 6dB. So, theoretically, the current run of the popular Motorola STBs would pass A/85 processed audio without alteration.

Test setup STB CALM compliance

To test this hypothesis, KABC, KNBC and KCBS in Los Angeles were monitored through a Motorola 7232 P2 STB from a Verizon FIOS fiber-optics feed. The test setup was configured to be like the one most viewers would employ, except our test computer replaced the sound system. (See Figure 1.) Figure 2 shows the results from these tests. The latest version of the Orban Loudness Meter (2.0.8) was employed with all levels measured per BU.1770-2 with three-second integration time and no gating. Results are in LKFS.

Anchor levels were somewhat subjectively derived from observation of the program elements, and are thus “apparent anchor levels,” which probably accounts for the small differences from station to station. Establishing equal anchor levels with and without compression was made more difficult by the fact that the 7232 STB output level increases by about 12dB when the compression option is turned on. This necessitated re-evaluation of the anchor levels for each mode. The target anchor levels were assumed to be -24LKFS. Also, each station was airing different commercials. Even so, the uniformity of the apparent anchor levels and commercial levels was astonishing for all stations measured. The same measurement routine was employed using the STB analog outputs, and results were essentially identical. These stations are obviously all doing a great job with CALM compliance.

Results of A/85 compliance tests

While these measurements with the current Motorola equipment are comforting in that the trend should increasingly be toward unaltered A/85 pass-through, the number and variety of older STBs that might have problematic audio compression is staggering. It was not practical to obtain various makes and models of older STBs and register them with a cable provider to enable off-air testing, but we know there is no way re-leveling A/85-compliant audio is a good thing. So, if you’re certain that your station is CALM-compliant, and you’re still getting loud commercial complaints after all the effort and treasure expended, you might consider the following steps:

  • Log all commercial loudness complaints from viewers and whether they are on cable or satellite.
  • Log the provider and, if possible, the make and model of STB.
  • Suggest that viewers with commercial loudness problems go to the STB settings menu for audio and turn off the compression or dynamic range reduction option.
  • Ask MVPDs in your area to deliver their boxes with audio compression off, and have them suggest to viewers who call with loud commercial complaints that they turn it off rather than on.

Overall, having a log to demonstrate a correlation between viewer commercial loudness complaints and viewer STB settings can obviously be extremely useful if those complaints find their way to the FCC.


Dennis Ciapura is president of Performance Broadcasting, a broadcast management consulting company.



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