One specific part of the BS.1770-2 revision is essential — the gating scheme when measuring program loudness. This method prevents, e.g., long periods of silence or atmospheres in a movie, to affect the overall measurement undesirably. In short, this means that it is now possible to align different types of (television) programs in terms of loudness. News, sports, commercials, concerts, talk shows and movies can actually co-exist without viewers having to adjust the volume over and over again, which is exactly what caused the complaints that led to the CALM Act in the first place.
The gate, however, is not the only difference between A/85 and R 128. While R 128 measures the audio signal in full with the employed gating scheme, A/85 aims at detecting the speech part of the signal and using that as an anchor point for the measurements. Although this method can work for determining gain offsets between dialogue-based programs of a certain genre, it has proven to be ineffective when it comes to aligning many different types of programs.
For instance, one obvious, potential problem is that not all programs contain speech, or use it like it is used in movies. Furthermore, who determines what is “speech” and what is not? The proprietary and patent-protected dialogue-detection algorithm A/85 relies on can sometimes interpret a violin as being a human voice, and conversely, not recognize a Swedish dialect. Under the “speech ruling,” it would also be easy for commercials to become even louder by just keeping dialogue softer than other elements of a mix.
Faced with these challenges, ATSC recognized that the dialogue-based approach was not suitable for aligning interstitials on TV, and consequently new annexes (J and K) added in July 2011 stated that commercials were no longer to be measured using the speech-anchoring approach, but that all sources had to be taken into account. However, regular programs are still recommended to be measured using speech anchoring, and consequently, broadcasters will have to switch back and forth between different ways of measuring whenever a commercial appears.
To avoid this, it might be worth considering switching to one transparent measurement method, based on open standards, that works across all types of program material.
The gating scheme
Obviously, the one measurement suggested above is available already, namely in BS.1770-2. Its key feature is the gating scheme, so let’s have a closer look at how that actually works.
The gate is activated when programs with a wide loudness range are being measured. In such situations, the measurement hones in on foreground elements and disregards the rest. In practice, the gate takes long passages of silence or background audio into account by pausing the measurement of parts dropping below -10 loudness units (LU) relative to a measurement of the same program material without the gate.
Note how the BS.1770-2 gate is not set at an absolute loudness level (such as -34LKFS), which would be impractical and necessitate a new measurement in case a level offset was performed. Measurement gating is also a good help on the application side: With the previous, ungated technique (BS.1770-1), random parts of silence before and after a program could influence the result, making it virtually impossible to obtain the same number twice.
As a net result of BS.1770-2, a station is now able to gain-offset (normalize) programs based on their foreground loudness, which is what the audience prefers to hear. Furthermore, with optimum gain-offset taking place at the station, little or no dynamics processing is needed, and it becomes easy to cater to various broadcast platforms at a high audio quality. Finally, BS.1770-2-based normalization grants programs more transmission headroom than if normalization was based on BS.1770-1, or if it was based on speech.