Loudness measurement was introduced recently by the EBU, foremost for TV and radio stations to end the “loudness war” and create smoother sound dynamics in the programming (an example: you’re watching a movie on TV, then the commercials cut in and suddenly everything sounds louder, even though, technically, it isn’t)
Steinberg has, to my surprise and delight, jumped on this wagon very early and with very pleasing results (their integrated loudness meter is superb)
The loudness meter works in several different ways, and quite differently as the classic meter.
First, and most importantly, what you’re measuring here is perceived loudness, meaning how loud program material will actually sound to a human ear. That means the reading is dependent not only upon what volume level your mix has (that’s the classic readout you know from previous versions, called “PPM metering”) but also how wide the dynamics of your mix are (lots of compression = louder material) and what frequencies are present in your mix (more stuff in the range between 200 Hz and 8 kHz = louder material)
The loudness meter measures this in LU (loudness units) as opposed to the classic dB reading.
On top, you have the momentary loudness, meaning the loudness of short transients like a crash cymbal etc.
Beneath that is the short-term loudness, which measures the loudness over a somewhat longer time-scale, giving you a better impression of how loud you mix is currently perceived by a listener.
Below that, you have the integrated loudness. This is the loudness of the whole program, from start to stop.
Finally you’ve got true peak (your classic PPM-reading) and, what’s probably most important for music production, your loudness range reading.
This will tell you how dynamic your mix is, so it can tell you a lot about you program material and if it is suitable for the task in hand. For example, if you’re producing the latest smasher club-mix for Chris Brown or whoever, you’ll want this reading in the low one-digit area. If on the other hand you’re producing classical music, this readout can gladly reach values of up to 20 LU (after that, it’ll be a bit hard on the listener though, unless he has a REALLY good HiFi…)
So the main question is: what are you doing? If it’s music, be it classical or hardcore techno, you will still need to deliver a mix that maxes out at -1 to -3 dB on the CLASSIC PPM meter, and then you can use the integrated and loudness range readouts to see if your mix is suitable for your audience.
If on the other hand you’re doing something for a (at least European) TV station, you mix will have to have an integrated loudness reading of -24 to -22 LUFS, ideally exactly -23 LUFS.
There’s a lot more to it, and if you’re interested in further details, here’s the exact specification from the EBU: