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Achieving consistent loudness measurement Part 1

With the recent passage of the Commercial Advertising Loudness Mitigation (CALM) Act, U.S. broadcasters are being forced to address longstanding consumer complaints about unwanted variations in the perceived volume of programming. These complaints generally focus on commercials, which seek to get the viewer’s attention through a variety of production techniques.

The CALM Act, which will not come into full effect until the end of 2012, mandates that the FCC enact regulations prohibiting commercials from being “excessively noisy or strident.” On a parallel path, the Advanced Television Systems Committee has adopted Recommended Practice A/85, which focuses on audio measurement, production and monitoring techniques designed to provide consistent loudness control across all DTV content.

An engineer by training and trade, Karsten Hansen is founder and CEO of audio and video metering specialists DK-Technologies in Denmark and is one of the world’s leading experts in the field. The audio monitoring system he developed for the BBC, installed at the Broadcasting House in London in the early 1990s, is still in use today.

Most broadcasters plan to address loudness monitoring and control through the acquisition of appropriate equipment. Having examined the loudness standards in both Europe and the United States, and the conditions and equipment used to comply with them, Hansen has found significant inconsistencies in the results produced on various measuring devices. For this reason, he has embarked upon an educational effort to help broadcasters achieve accurate compliance with their local loudness standards.

“Many broadcasters have asked, ‘Why it is so hard to measure the same level all the time?” Hansen said. “My advice to them is: Don’t panic! Like most elements of broadcast, the important thing is to understand best practices and implement them. Just as the VU meter is not the appropriate tool in the digital domain, things that have been good practice for many years have to change. But once you understand the problem, the solution is not difficult at all.”

To assure compliance with loudness standards (ATSC Recommended Practice A/85 in the United States), Hansen has developed a straightforward set of guidelines for broadcasters, content producers and post-production houses. By following these straightforward procedures, users may be assured that the loudness measurements they take will be both accurate and compliant:

  1. Measuring equipment: Use loudness measurement equipment from a trusted manufacturer. This trust can be best established through some straightforward confirmation testing.
  2. Digital interface: It is critical to prohibit sample-rate converters within the system, because converters change the signal and skew the results.
  3. Transient response: Test to confirm that true-peak measurements comply with benchmark testing using one-sample and two-sample -6dBFS (full-scale) tests.
  4. Static and dynamic performance: Use a tone generator to perform channel sum and tone burst tests to confirm readings in sliding and integrating modes of the loudness meter.

As a test and measurement specialist, Hansen feels it is critically important for broadcasters to apply the same strict quality standards to loudness that they use throughout the broadcast chain.

“In developing these rules, I approached things from a strict engineering perspective, with no agenda beyond analyzing and resolving the problem,” he said. “We are totally loyal to all the international standards that our customers must follow and make no judgments about them. The standard drives the procedures, not the other way around.”

In the next issue of “Audio Technology Update,” Karsten Hansen will explain the specific test procedures broadcasters can use to confirm that their loudness measurement system is accurate and reliable.