A few nights ago, I was struck by an idea that hadn’t occurred to me previously. I was prepping for a presentation on loudness metering at a game development studio that would take place the following day. It was a question…
Would bit rate or sample rate reduction affect the loudness measurement of sounds metered using ITU-R BS.1770?
Both are practices common to game audio. If there actually is a potential difference, it would be important for people to be aware of that. Never blindly trust your tools. We use metering systems, because it is unwise to rely only on our ears. Likewise, trusting a metering system in a situation it may not have been designed for is equally foolish. With everyone constantly pushing for higher quality and higher resolution audio, I doubt there was an abundance of concern during the development of ITU-R BS.1770 for possible applications in lower resolutions.
Guest contribution by Owen Green
[This is the second of a two part series on loudness, mixing, metering and the new ITU loudness spec]
The New Loudness Standards, and What They Might Mean for Us
Depending on the field in which one worked, standard production practices have tended to be orientated around peak normalisation of material. That is, lining up recordings by their peak level; in music, recordings are now often lined right up 0 dBfs; in broadcast a common specification is to peak at -9 dBfs (which allows some headroom in recognition of the fact that analogue QPPMs don’t truly measure signal peaks). As is hopefully clear from last week’s article, this has almost no bearing on how loud we perceive the material to be.
A set of new recommendations has been developed since 2006, and are now becoming standard or legally stipulated practice in some industry areas and countries. It is therefore worthwhile to get a handle on what they mean, and how to use them as soon as possible.
The core proposal comes in the form of a recommendation from the ITU (International Telecommunications Union) on how to measure the loudness of a signal (ITU BS.1770-2). Local bodies, such as the EBU in Europe and ATSC in the US, have then published (pretty similar) guidelines on working practices derived from the ITU spec. The common thrust of these proposals (actually, now rules in some places!) is that they enable a move away from normalising by peaks to normalising by (approximate) loudness:
So, material that has been more compressed in dynamic range (so as to appear louder when peak normalised) loses its ‘advantage’ by being reduced in gain
so that its perceived loudness is on par with more dynamic material.
If you missed Saturday’s webinar, the recording is now available. Just click here to load it up.
We had some reports of audio issues, which appear to be due to the service’s compression settings. All of the truly pertinent information is included in the slides that were part of the presentation. So if things get a little difficult to make out sonically, don’t fear that you’re missing out on important data. We’re looking into how we can correct this for future presentations.
At the end of the presentation, I put up a set of URLs. I’m including them here for your convenience:
Listening Examples – A set of 150Hz and 2500Hz sine waves, and pink noise files…normalized using different metering standards (RMS, LeqA and BS.1770). Just right-click and download.
ITU-R BS.1770 – Documents outlining the metering spec
EBU-R128 – The European broadcast recommendation
ATSC-RP A/85 – The broadcast recommendation from the United States
C.A.L.M. Act – Information about the legislation passed in the U.S. regulating commercial advertisement loudness
And, as I said at the end of the webinar, feel free to e-mail me if you have questions or need clarification on anything covered in the webinar. Or better yet, leave a comment below for me to respond to. That way we can avoid repeats of the same questions.
We’re changing the name of the “Film Sound Discussion Group” to Designing Sound Discussion Group, because it’s silly to think that we’ll never have a live discussion about anything other than film. While I’m on the subject, it’s also high time we scheduled the next webchat!
As the title of the post suggests, in the next presentation I’ll be explaining how, exactly, ITU-R BS.1770 compliant metering methods work, and the standards and applications that have been developed to make use of “loudness” metering. We’ve already mentioned that February is going to be “loudness” month (bottom of the post), and we’re setting up the first full week to make sure everyone can get a strong grasp of what it all means, even if you’ve never explored the subject before. We’ll be capping the week off with this webinar on Saturday, February 9th, at 11AM (U.S. Eastern Standard Time).
I’m trying to make this presentation as accessible as possible. Don’t worry though, there will definitely be time at the end of the webinar for questions. If you can’t make the webinar, a recording will be available within the following few days.