Ever notice how the volume on your TV seems to get louder when the commercials come on? The US Congress sure did. And earlier this month it passed the CALM Act, which orders the Federal Communications Commission to figure out how to make it stop.
To understand why that will be a huge challenge, it helps to learn about dynamic range compression of audio. Dynamic range compression is the electronic process of reducing the difference in volume between loud and quiet sounds. That can create the perception that the overall volume has been increased.
KUT engineer Jim Reese says it's those kind of technical considerations that will make TV volumes difficult to regulate.
KUT News: How technically difficult will it be for the FCC to regulate the volume of TV commercials?
Jim Reese: It is difficult for several reasons, the main one being that loudness is very subjective. There are a lot of things that can contribute to something that sounds loud. Whether or not they're talking about absolute level versus something that has been compressed to reduce the peak-to-average ratio is going to sound louder, even though it may not be any louder in real level.
I think it's going to be hard to write regulations that are both effective and technically feasible. It's going to be interesting to see what they come up with.
KUT News: You have a lot of dynamic range in TV programming, but once you hit commercial, the audio is extremely compressed.
Reese: What they do in the programming is a lot of times, they'll exaggerate the dynamic. In other words, they're going for the shock value of a noise, a gunshot or a door slam or something. They'll reduce the average level of a program. They'll have a quiet part in the program, and it will be punctuated by something that's supposed to get your attention. That's one issue.
The other issue is that a lot of times, a program that's edited for TV is going to have the commercial breaks built in. It's going to fade out. Then you're going to get hit with whatever is the next thing. The commercial guys, they have the opposite approach. They want it to sound as loud as possible, so they're going to compress it to reduce the peak-to-average ratio. So even though it's not really any louder on a VU meter, it's going to sound louder.
A lot of what they're going to have to regulate if they're going to make this effective is they're going to have to say you can't overly compress. Now, every broadcaster puts compression on their audio for no other reason than most source material has more dynamic range than the transmitter can reproduce. You have to have some sort of compression because you can't transmit it as it comes in.
KUT News: It sounds like they're going to have to regulate not only volume levels but also dynamic range.
Reese: Right. In order to be effective at all, they're going to have to base it on average levels rather than compression or something like that. It's going to be really hard to make something compressed not sound louder, because it's a perception thing.
KUT News: Would that be hard for the engineers to implement?
Reese: I think it's going to be difficult to create rules that are fair. There are things that are going to be intentionally compressed for effect, and there are going to be things that are intentionally expanded for effect.