The following article is presented as a tutorial for AMIA members. While it describes techniques and specifications for new finished audio soundtracks on programming intended for television broadcast which may include materials from your vault, please bear in mind that these techniques and specifications have not yet been passed into law in the United States. Furthermore, since most archives are not called upon to deliver finished, air-ready programs, these techniques will, if passed into law, be required of those who do deliver the finished programs. As mentioned in the article, certain broadcast facilities are already requiring these specifications for their incoming, new programs and as time passes, other broadcast facilities may join them in these requirements.

As a matter of historical note, you should be aware that manipulation of track levels by broadcasters is nothing new. Since the earliest days of analog broadcasting, automatic leveling was employed to restrict the dynamic range of audio as the final step of electronic processing prior to transmission. Perhaps the most exaggerated example of this was to be found in the 1950's production of "Victory At Sea" where, for the sake of maximum signal-to-noise during reproduction, the orchestral music track was recorded as loud as possible on the optical track and only lowered to normal levels when there was voiceover narration. The finished track depended on the transmitter audio limiters to bring the combined mix into balance.

More truly obnoxious examples can be found today when commercials are dropped into otherwise normal programming at levels (which by comparison) would wake the dead. It is this situation that the following article addresses.

Loudness Goes Legal
by Chris Reynolds

There has long been disagreement as to whether or not loudness can be measured objectively. Over the past few decades, countless tests have been conducted to come up with an accurate way to measure loudness as humans perceive it. Because volume preferences vary from person to person, it has been difficult to remove the subjective aspect of loudness measurement. Some people like their music loud, some like it soft. Some like explosions to shake their house while others don't want anything shaking at all.

Using information from various studies, researchers have succeeded in creating a new multi-channel loudness measurement algorithm that reflects how humans perceive loudness with an accuracy that was previously unattainable. The first version of this new algorithm was defined in an ITU (International Telecommunication Union) broadcast standard recommendation in 2006 (ITU-R BS. 1770-1). The new measurement scale is referred to as LKFS (Loudness, Kweighted (frequency weighting) relative to Full Scale).

The ITU recommendation also defines a new digital peak metering measurement system called "True Peak (TP)." TP allows for more accurate peak measurement of digital audio by analyzing the analog waveform derived from the digital signal. During digital-to-analog conversions, such as from a digital amplifier to loudspeakers, the peak level of the analog signal can actually exceed that of the measured digital sample peak, causing distortion and unexpected overloads in various stages of audio distribution and reproduction.

These are important developments for the providers of audio/video content because consumers are increasingly unhappy with the inconsistent levels they've been subjected to during digital television (DTV) broadcasts. In the days of analog television broadcasting, the audio tracks needed to have their dynamic range (difference between the quietest audio portions and the loudest program content) reduced. This meant that a lot of audio compression was applied to minimize the dynamic range between the quietest and loudest sections of program. The amount of compression that engineers used for this was not based on loudness, but on VU meter measurements and analog peak levels. This heavily compressed audio resulted in a normalized loudness level to which analog TV viewers became accustomed. However, it also diminished the listening experience. As DVD, Blu-ray Disc, and digital download/streaming services began delivering audio content with full dynamic range to consumers, it became clear that the analog broadcast system needed to be updated.

That updated system is DTV, and it allows broadcasters to deliver more dynamic audio content while applying little or no compression. Unfortunately, it also highlights the level discrepancies between programs and commercials. Consumers vigorously complained to legislators that they constantly have to adjust audio levels up and down when watching television. Because of this, new federal legislation has been drafted requiring all broadcast audio to fall within a predetermined range. This legislation, named H.R. 1084 - also known as the CALM (Commercial Advertisement Loudness Mitigation) Act - has passed in both the House of Representatives and the Senate. After some minor changes are made, the CALM Act will surely be signed into law. The theory of this legislation is that if all programs are measured and adjusted to have the same overall loudness, consumer complaints over level discrepancies will decrease.

The CALM Act calls for compliance with a 2009 ATSC (Advanced Television Systems Committee) technical recommendation, A/85, which states that the "current version" of ITU-R BS. 1770-1 be used for all loudness and true peak measurements. Furthermore, it mandates that all broadcast material must have an average loudness of -24LKFS using dialog as an anchor point, and that the maximum level should not exceed -2dB TP (decibels true peak).

In order to meet these requirements, program material must be measured in its entirety for an average LKFS reading, after which the overall program level will be raised or lowered to achieve -24LKFS.

The EBU (European Broadcasting Union) has conducted its own loudness studies and agrees that the ITU-R BS. 1770-1 algorithms are very good, but it has also published additional recommendations to improve its accuracy and satisfy consumers. In addition to requiring a slightly different program loudness average (they're asking for -23LKFS as opposed to -24LKFS), it recommends intelligent gating processes and a maximum Loudness Units (LU) range. Based on additional studies, the EBU feels that consumers are interested in having more dynamic range, but not as much as A/85 allows. They advocate setting maximum LU ranges to minimize consumers' tendency to reach for the remote to adjust the level between programs and commercials. The ITU has been reviewing the EBU recommendation and is reportedly considering implementing many of the recommendations. As A/85 requires following the latest version of ITU-R BS. 1770-1, any updates based on the EBU recommendation will become law as part of the CALM act.

Just two years ago, taking these average measurements to comply with the CALM Act would not have been possible, but new audio meters are now available that contain both the ITU-R BS. 1770-1 and the EBU algorithms. Measurements can be derived, in real time, by playing the program through the meters - or even faster than real time if audio files are used. Software can analyze the audio files and derive the measurements in upwards of 8x real time (about 15 minutes for a 120-minute feature).

While the CALM Act and the EBU recommendations have not yet become law, major networks in the United States and abroad (such as NBC/Universal and Sky Italia) are already requiring that content delivered to them conform to these new guidelines.

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