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LUFS, dBFS, RMS… WTF ?!? How to read the new loudness meters

by Ian Shepherd


 
 
LUFS, dBFS, R128, dBTP, ITU BS 1770, ATSC A/85, TT DR

WTF ?!?

There are now so many ways to measure your music these days, it’s not surprising that one of the most common questions I get asked these days is

What do all these acronyms mean ?

In particular, people want to know about the new “ITU-based” loudness meters, which use mysterious new “Loudness Units” – LU for short, or LUFS to be more technical. Especially as mainstream software like Cubase 7 and Ozone Insight begin adding support for them.

You know they’re important, you know that meters using the new system are appearing in more and more places – but how do you know what they mean ?

Well the good news is, it’s not as complicated as it seems. There’s a pretty simple relationship between the new LUFS measurements and the loudness measurements we’re used to, like the TT Dynamic Range Meter’s DR value, or good old RMS average levels.

The video above demonstrates all of this, as clearly and simply as I could make it – as well as an important complication with RMS levels that everyone needs to know about.

You can download the “pink noise” test file I use in the video to try this for yourself here.

The loudness meter I use in the video is the excellent Meterplugs LCast, and you can find out more about the Music Loudness Alliance here.

I hope you find the video helpful, and let me know if you have any questions !
 

Appendix: Get your RMS right !

I mention in the video that some DAWs and meters use the wrong method to measure RMS for music, and so many people have asked me about this I thought I’d add some more detail.

RMS can be calibrated using either a full-scale square wave, or a sine wave. The correct way to do this for a music signal, as defined by AES Standard AES17-1998, is to use a sine wave peaking at 0dBFS – for more details, click here.

If a meter is calibrated using the wrong standard, the RMS level will under-read by 3dB, and you’ll be tempted to mix or master everything too loud.

Here is an (incomplete) list of DAWs and meters this has been tested in:

Correct

Wavelab
TT Meter
Ozone 5
Waves Dorrough
Voxengo SPAN

(Actually by default it’s wrong but this can be corrected using the “RMS +3dB” preference)
Reaper is about right, but the time constant needs to be correctly set to 300ms

Incorrect

Slate FG-X
Waves PAZ - 4dB off (?!)
Waves WLM
Logic 9 Multimeter
T-RackS (New version not yet tested)

 

Test for yourself

Simply download the pink noise file here and try it in your own DAW or meter – the RMS level should read very close to -11.5 dBFS. If it doesn’t, something is wrong.

And, please feel free to report the results of your own tests in the comments.
 
 

facebook comments:

14 Responses

  1. Thanks for the overview. I understand most of this a lot better now, but I have two questions:
    1) You lost me when you compared the meters with the TT Meter. You were comparing LU, Dynamic Range, and RMS, but all of your values were at or around 9, so I couldn’t correlate anything. Is it possible to give an example where the values are different?
    2) -23LU seems like it’s really really quiet. Doesn’t that mean that we’re going to be mixing and mastering at much lower levels? I get that I can mix/master as loud as I want and it will just be turned down, but if I aim for -23LU when mixing, that’s about like mixing at -23dB RMS, isn’t it? That’s roughly 13dB quieter than we mastered at in the HMM.

  2. Ian Shepherd says:

    Hi Tim,

    1) If the signal is peaking at close to zero, the values will always be similar. So if the RMS is -14, the LUFS will be roughly -14, and the DR will be roughly 14.

    I say roughly, because both LUFS and DR employ “gating”, meaning they assign less priority to low-level signals than pure RMS, and LUs also take account of the ear’s frequency-sensitivity, to a certain extent – but as a rule of thumb, it’s not too bad.

    The exception is the DR – if you have a DR10 signal, and turn it down by 6dB, both the LUFS and RMS readings will also fall – but the DR will stay the same, assuming it wasn’t heavily limited or clipped to start with.

    2) -23 LUFS seems quiet in comparison to the absolute levels on CDs because it is – so there is enough headroom for classical and especially feature film material at a similar playback volume. I don’t recommend -23 LUFS as a guideline for mixing or mastering – I think somewhere between -14 and -18 is fine, assuming there’s no clipping.

    But really, the absolute level when mixing shouldn’t be critical in general – it’s only when mastering that it becomes an issue.

    At that point, my recommendation is to aim for an *integrated* value of -12 LUFS (over an album with a fair bit of contrast) averaging a momentary -10 LUFS reading during the loud sections and peaking at -8 LUFS – which corresponds closely with what I suggest on the Home Mastering Masterclass course.

    Whereas plenty of recent releases are up at -6 LUFS or higher almost all of the time… BUT as the ITU guidelines are implemented more and more widely, no-one will ever hear that !

    Ian

  3. Thanks, Ian. that helps a good bit. I wish the meter manufacturers were making recommendations similar to yours. The meter you used in the video had adjustable thresholds, but most of the cheaper/free ones don’t, and working in the -12 to -10 range is squarely in the red on the meters. That gets confusing for folks. I know how to read my TT meter, but all of the LU meters confused me and seemed to be saying “YOU’RE WAY TOO LOUD!” Maybe I can start using them more now that I have a better understanding.
    Oh… but I do love that TT Meter, 32-bit bridge on Logic and all….

  4. Ian Shepherd says:

    Yeah, the thing is those recommendations are using the broadcast standard – since so far there IS no standard for CD. It’s confusing, I agree.

    And yes – the original TT meter is still one of the best !

  5. Jim Williams says:

    Great video Ian.

    This is all excellent news and could rescue recorded music as a commercial art form. I don’t think there is much wrong with the CD format. I believe people started thinking CD sound sucked simply because of the audio fatigue syndrome associated with hyper loud masters.

    Sure, 24 bit/44.1 (etc) is notably more enjoyable and revealing on well recorded and mastered music but I’d settle for properly dithered 16/44.1 if future CD releases were mastered to the new standard.

    With the current state of consumer technology we are now at a point in time to deliver, commercially, fantastically dynamic and well recorded music to the masses and given these new standards we may see Joe Public start to appreciate music from an audiophile perspective.

    As an aside, it’s interesting how films have been forced down the route of music where people are seemingly content to watch films on Youtube etc, in dreadful quality – just like they do with music and mp3s.

    One final point: Part of me wishes they’d pick -20LUFS over -23, just because it falls in line with K-20 nicely which is a good standard to work to, allows for good dynamic range across many platforms of music and matches up with 0VU/-20dbFS if your hardware is calibrated that way.

    I look forward to punters using their volume knobs again when a song excites them so much that they want to hear it louder – and with the dynamics intact!

  6. Joel Walsh says:

    The TT meter is still my go to reference. Thanks for taking the time to share Ian !

  7. Stone Walters says:

    Hey Ian. I thoroughly enjoyed this video and it shed much light on what can be a perplexing subject, so thank you for explaining it in such simple terms.

    My one question was going to be about whether to aim for -23LUFS when mixing for radio but Tim beat me to it! If I understand your response correctly somewhere between -18 to -14 LUFS is a good level for mixes to come in at providing there is no clipping. Based on your ‘Headroom’ article mixes should ideally also have headroom of -6dBFS (when measuring peaks). Shooting for these targets whilst mixing should allow the mastering engineer enough scope to do what they do best, creating a scenario in which mixes are compliant with current/new broadcast standards. Do I have this correct?

    Thanks!

    Stone

  8. Ian Shepherd says:

    Hi Stone,

    Almost ! If a mix is reading -18 or even -14 LUFS, I think it’s safe to peak right up near zero.

    If you want to play it safe and have 6dB of headroom, I’d make sure the integrated loudness is adjusted down accordingly – between -24 and -20, say.

    Ian

  9. Stone Walters says:

    Hey Ian,

    So if the mix comes in at -18 to -14 LUFS that means it’s OK to peak close to zero and still be one of your mastering engineer’s favorite clients! I think I’ve finally got it!!!

    Thanks again!

    Stone

    PS You also mentioned that you cover this info in more depth in one of your courses. Which video/ebook is this?

  10. Mark Hawkins says:

    With the release of Logic Pro X, I was playing with the Waves WLM today with the pink noise file since the TT DR Meter no longer works with X’s 64-bit mandate. Watching this video, it seems to suffer from the -3 db lower issue you described. I’ve tried the various options in the plugin but don’t really see a way to adjust the reading. Why does WLM use the lower reading? Is it a problem? Is there a way to fix it other than use another meter. :-)

    Thanks in advance!

    -Mark

  11. Ian Shepherd says:

    Mark, I think Waves PAZ uses the right value – the WLM is an R128 meter though, it shouldn’t show the problem…?

  12. Kahlbert says:

    Hm, I see a difference between “true peak” and “normal” meters but I’m not sure about that math there.

    The level meter (plugin) in Studio One normally shows the correct level, but is also 3 dB off when switched to TP. So that might be the reason why WLM is off as well …?

    On the other hand, K-meters show the correct level, too, but aren’t they meant to be true peak?

    Dang, I really thought I had understood the whole level thing years ago …

  13. Jeroen Wolff says:

    Hi Ian, what do you mean by “Reaper is about right, but the time constant needs to be correctly set to 300ms”
    Because in my Reaper it shows almost 0 dB FS RMS, far from the supposed -11.5 ?

  14. Ian Shepherd says:

    Something must be wrong somewhere – that sounds more like the peak level.

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