Not sure what all this loudness stuff is about and how it affects you? Confused about the difference between LKFS and LUFS? In part two of a four-part series, loudness expert Mike Thornton continues to answer these questions and many more in his premium tutorial series, which is now available for free.

In Part 1, Why Do We Need Loudness? We clarified what we mean by loudness, investigated how our hearing works, why we have changed our audio metering systems and presented the solution to loudness changes that consumers complain about.

This article and free video tutorial will cover the development of one loudness standard. We explore how we arrived at a loudness measurement algorithm that works just like our ears and the various criteria we use to define and guide us when working to the new loudness delivery specifications, including K Weighting, the differences between Momentary, Short-term and Integrated loudness as well as the importance of True Peak and Loudness Range.

One Loudness Standard For Music Production And Audio Post-Production

Following many years of research into how our hearing works and how we perceive sound, together with many hours of listening tests by organisations including the Communications Research Centre (CRC) and McGill University in Canada, the standard BS1770 was drawn up.

Without getting into all the technical details, a K-weighted filter curve, based on the research results from all the listening tests, builds a bridge between our subjective impressions of loudness and the need for an objective measurement we can use to make comparisons.

The K-weighting method is an essential part of the global, open standard BS1770 defined by the International Telecommunication Union. That said, BS1770 has gone through a number of tweaks along the way.

Meters measuring loudness using K-weighting produce a measurement with a unit called LUFS or LKFS. Note that there is no difference between LUFS and LKFS, they are two labels for the same thing and are completely interchangeable. 

It also helps to use a relative scale so our target loudness becomes 0LU making it easier to read the meter, a bit like 0dBU as an absolute measurement and -10dB being a relative one. Also, it is useful to know that a change of 1 LU is equivalent to a 1dB change.

When the BS1770 standard was set they determined how a compliant meter should measure the various parameters but they rightly chose not to specify how a compliant meter should look. As a result, there are a range of meters to choose from.

All BS1770 meters have a minimum of 3 loudness measurements, all of which are averages.

The first two, Momentary and Short Term, are tools to help us mix content that will be loudness compliant but they don’t normally form part of the delivery specs.

• Momentary (M) averages the loudness over the last 400mS

• Short Term (S) averages over 3 seconds.

• Integrated (I) is an average over the complete program so far.

At the end of the program, it is the Integrated measurement that is one of two measurements that will determine whether a program will pass or fail. The other measurement that will pass or fail a program is the true peak level.

What Is Special About True Peak?

Interestingly, with the introduction of loudness metering, peak metering is not dead. In fact, because we are working so much closer to digital headroom we need much more accurate peak metering, we just are not using it as a way of matching programs anymore.

True Peak differs from Sample Peak in that true peak looks at what might have happened between the audio samples. To be absolutely sure exactly what is going on, to measure what we now call the true peak value requires a meter to read 4 times faster, so making 192 thousand measurements per second enables us to establish what is happening between the samples.

This is really important as we are now working within 1 or 2 dBs of digital headroom and true peak readings can be up to 6dB higher than sample peak measurements. Because a program can pass or fail on True Peak it is essential we measure the peaks of the audio using a true peak meter and where limiters need to be used to make sure the audio never goes above the maximum permitted and that all limiters be true peak limiters too.

The green blocks represent the Loudness Range for different types of content

What Is Loudness Range?

Coming back to our loudness meter, there is another measurement BS1770 compliant meters take and that is Loudness Range.

So what is Loudness Range? It’s another measurement that we can use in conjunction with Momentary, Short Term, Integrated, and True Peak and gives us a measurement of the range of the loudness in a program, so how much light and shade there is. Normally a program will not be failed for too much or not enough loudness range. Rather it is a tool to help us get a sense of the amount of variation in loudness in a program. However, more recently some broadcasters and publishers have started to recommend Loudness Range guidelines.

The range is described in LU, and to avoid occasional extreme events from affecting the overall result, the top 5% and the lowest 10% of the total loudness range are excluded from the LRA measurement. For example, a single gunshot or one long passage of silence in a movie would result in a higher Loudness Range and skew the result.

Loudness Range is also a useful indicator of potential dynamics reduction processes in a signal chain, perhaps if the program is also going to be delivered on a mobile platform it might be necessary to take steps to reduce the loudness range to suit that delivery platform.

One Standard - Several Delivery Specifications In Audio Post-Production

Although we have the benefit of one universal worldwide loudness measurement standard, we have a range of delivery specs around the world. The two major groupings of delivery specifications are ATSC A/85 for the US and Canada and the EBU R128 for Europe. There are other delivery specs in other territories like Japan and Australia but ATSC A/85 and R128 are the key profiles that most delivery specs are based on.

 As you can see from this table, they are all very close. When it comes to broadcast delivery specs, we will look at online and streaming later in this article.

The key difference now is 1dB or 1LU!  ATSC A/85 uses a loudness reference of -24LKFS, whereas EBU R128 uses a reference of -23LUFS.   R128 specifies a maximum of -1dBTP, whereas ATSC A/85 specifies -2dBTP. 

There were bigger differences in early versions of A85 and R128 but now they have converged significantly. For example, early versions of ATSC A/85 didn't specify the gate, but the gate is now in the current version of A/85.

Misconceptions About Working With Loudness

Just before we finish, I would like to touch on a few misconceptions about working to this loudness standard.

Firstly, some people have assumed wrongly that content normalised to loudness has no dynamic range. I believe this misconception has grown out of a misunderstanding about normalization. We have got so used to normalizing up to a maximum, with peak normalization where as Loudness is about a centre of gravity, the average over the whole program. To have an average, there must be lower and higher values, which produce an average somewhere inside the range between the highest and lowest. Just as every object has its own centre of gravity, which won’t always be in the middle, so every program will have an integrated loudness figure (the average over the whole program), but the overall position of that average will vary, depending on the shape of the program, and that is OK, it’s more than OK, it is the way it is meant to be.

Advantages Of Mixing To A Loudness Standard

To conclude, what are the advantages of mixing to a loudness standard?

• As audio professionals we get to determine what a program sounds like and have the confidence to know that the program we mix will be the same as the program the consumer hears and that it won't be messed about with downstream by any processing.

• Because of this, it’s very important there are no black boxes in the TX chain. Some broadcasters have been sold a black box that, if inserted in the TX chain, will make them loudness compliant; in my opinion, they cause more problems than they solve and, most importantly, fly in the face of the spirit of the concept of loudness normalization and bringing the control back to the audio professional.

• We can now make programs with more dynamic range, not less, because we no longer need to hit the ‘zero’ as hard as possible to make our program stand out.

• We are no longer constrained by quasi-PPMs. Calibrate your monitoring, and then trust your ears. They are still the best loudness tools we have.

What Next?

In Part 3, Calibrating Your Monitors, we will cover a key part of delivering loudness-compliant content - how to calibrate your monitors.  We will look at how our monitoring should be configured and provide an explanation of bass management and what your sub should be doing before moving on to a practical demonstration of how to calibrate your monitoring with a sound pressure meter.

In part 4, Creating Loudness-Compliant Mixes For Broadcast And Netflix, we will share some tips and tricks for mixing to the broadcast loudness standards for a wide variety of genres. We will include examples and demonstrations as well as explain the importance of what Mike describes as ‘loudness planning’ before ending with some specific tips and tricks for mixing short-form content like adverts, trailers and promos. 

In part 5, Preparing Content For Music Streaming Services, we will cover loudness online content and music streaming services, including the various standards for online content, loudness normalisation, album normalisation, and how to prepare music tracks for music streaming services with three free video tutorials.

In part 6, Using Loudness Meters For Music And Post Production, we will end the series by listing our selection of loudness meters in alphabetical order, and as we mentioned at the start, please note that this isn’t an exhaustive list. Where we have them, we will include tutorials and reviews of each of the meters.

Why Is It Now Available For Free?

This series, originally released in 2016, was on our premium tutorial channel, and since the platform they were hosted on closed down, this much-loved resource has not been available. Rather than find another platform, Mike has decided to make the entire course available completely free. We will be releasing the complete series over the coming weeks, all of which you can access completely free.

In just over 1 hour, Mike Thornton helps you understand how the new loudness standards affect you and the clients you work for. Mike has been delivering loudness training courses to broadcasters in the UK, Europe and further afield, and with this tutorial series, you too can benefit from his expertise.

Who is this course for? 
Although it is aimed at people working in broadcast and OTT environments, they need to produce content to comply with the loudness delivery specifications like ATSC A/85 for the US and Canada and EBU R128 for Europe, including live audio mixers, audio post-production editors and mixers, compliance teams, as well as video editors, and others working in the delivery of broadcast content, the first three tutorials in the course will be very helpful for people working in music production, who need to deliver loudness compliant mixes to any service using loudness normalisation.

What does the course cover?
In this series, we start by answering the question, ‘Why do we need loudness?’ We go on to cover the difference between peak level normalisation and loudness normalisation. We look at the history of audio metering and how the loudness standard has been developed and learn that the different delivery specifications around the world are, in fact, all based on that one standard. We show how to calibrate your monitor speakers, which is an essential part of mixing to loudness, before moving on to some tips and tricks on how to mix to comply with the new loudness standard and delivery specifications. 

How Much Does This Tutorial Series Cost?
This course was available for rent on our premium tutorial channel and cost $49.99 for one year. It is now available completely free at no cost.