The Levelator™ Loudness Algorithms

Over on the discussion mailinglist from AIR (The Association of Independents in Radio), we’re revisiting the recurring discussion about RMS levels in spoken-word audio files. Two days ago Gregg McVicar asked: “So what was the RMS value that you found to be the sweet spot for podcasts?”

Unfortunately, it’s a very complex answer. I’m not trying to be elusive or secretive. It really is complex. There isn’t a single value that works for even two different audio-editor applications let alone all of them. If I posted a realistic spoken-word .wav file and said, “this is standard,” and then you measured the RMS level of that track in various apps such as Pro Tools, Sound Forge, Soundtrack Pro, etc., each app would give you a different value. (Try it!)

The reason is ‘silence’. Each application has a different way of excluding segments of silence from the RMS calculation. In fact some of the most-expensive utilities don’t exclude silence at all, rendering them virtually useless for this aspect of spoken-word processing. (Is one recording half as loud as another because the speaker in the first one pauses twice as long between words?)

So the answer to Gregg’s question is that The Levelator adjusts speech to -18.0dB RMS, but that isn’t a value you can plug into any other program. If you are looking for an answer relative to your audio-processor of choice, the best way is to run a real-world program through The Levelator then measure the resulting RMS level using your software. The level your application reports as the RMS level is *your* answer to what we’ve found to be the sweetspot for podcast RMS levels.

Personally, I love the discussion of RMS levels, particularly because it’s so full of prejudices and misinformation. But I’m sure it’s not as interesting to many other people. It’s a problem I’ve worked on personally for some time, and I continue to geek out on it. If you share my passion on the topic, or if you want to know more about how The Levelator deals with RMS levels, you may enjoy a page I just posted entitled The Levelator™ Loudness Algorithms.  I would have posted this earlier, but I wanted to first run it by Bruce Sharpe, our resident math professor and designer of The Levelator’s algorithms. I’m just the concept guy on this one. 🙂

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