Not sure what all this loudness stuff is about and how it affects you? Confused about the difference between LKFS and LUFS? In part three 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.

What Has Gone Before

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.

In part 2, The Development Of One Loudness Standard, we covered the development of one loudness standard. We explored 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.

This article and free video tutorial 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.

Why Calibrating Your Monitors Is A Key Part Of Delivering Loudness-Compliant Content.

In my article Are TV Mixes Getting Too Big For The Domestic Living Room? I took an initial look at this issue. The National Association Of Broadcasters Engineering Handbook states that larger rooms with a higher reference SPL will yield wide dynamic mixes, whereas smaller rooms with a lower SPL will yield more constrained mixes.

We know from the various standards, including the ATSC recommendations, that the recommended sound pressure levels for larger rooms are higher.

Categories of Audio Control Rooms Used In Television Production

Sound Pressure Level For Different Size Audio Control Rooms

Please use these tables as a guide to start form, but don’t be afraid to deviate from them if you find your mixes are routinely too loud or too quiet. The key is to find a calibration point that is right for you so that you deliver loudness compliant mixes without looking at the meters.

It doesn’t matter if you are working in surround or stereo, the principles are the same but for the purposes of this demo I am going to use a stereo system.

Your speakers should be all the same whether for stereo, surround, or immersive however on a surround system if space or budget area constraint, then the front three speakers should be the same but the surrounds could be smaller speakers from the same brand.

The Role Of The Subwoofer In Professional Studio Monitoring

Bass management and LFE are two different issues that are often handled by the same speaker, especially in smaller systems, and this can cause confusion.  

As audio professionals, it is generally recommended that we try and avoid using bass management. Bass management is necessary where the main speakers are unable to handle the very low frequencies in normal audio content, usually because they are too small. In this case, the system is designed to redirect the very low frequencies to the subwoofer, a single speaker designed to handle very low frequencies, and because low-frequency sound is not directional, it doesn’t really matter that it is all coming from one speaker.

In surround monitoring systems, the LFE channel requires the use of at least one subwoofer in the monitor system, but this should only reproduce what is in the Low Frequency Effects or LFE channel.

The Importance Of Monitor Level Calibration

Monitor Calibration is really important. Because our ears are excellent at perceiving loudness, if we set our monitoring so that we play sounds at the same volume level, we will naturally mix loudness-compliant content without having to be glued to the metering. We will be able to work to that consistent loudness centre of gravity.

We use a sound pressure level meter to calibrate our monitoring, but although there are recommended levels for different sizes of rooms, my advice is not to feel bound by them. Essentially, the smaller your room is, the lower your listening level should be.  Unless you’re in a mixing space that is the size of a movie theatre (and has similar acoustics), 85dB-SPL will simply be too loud. Again we are picking up a standard that has come from the film workflow, but most broadcast sound is not mixed in film dubbing theatres, we work in much smaller spaces hence the smaller the room the quieter your monitors will need to be.

You can see from the table above some recommended levels for different sizes of mixing rooms. Use them as a guide to start off with, but don’t feel tied to them. Start off with the most appropriate sound pressure level for the size of your room.

Then start mixing and see how you get on. The key aim is to find the monitor volume that works for you where you naturally mix loudness-compliant programs without looking at the metering. If you find that, having calibrated your monitors based on this table, your mixes are coming out too high or too low, then adjust your monitor volume by the corresponding amount until you mix bang on the mark. If you get this right, you should be able to mix content within 1LU of your target loudness.

How To Level Calibrate Your Monitors

You’ll need two things to calibrate your monitors: a pink noise file and an SPL meter. A low-cost meter like this one is absolutely fine. These meters come with several different ‘weighting’ systems built into them, which are similar to, but different from, the K Weighting used in the BS1770 standard. For this application, you should use a “C-weighted” curve and the “slow” response setting.

You can use an app on your smartphone, but be aware that they may not be calibrated, so they won’t give you an accurate reading. The ones on Apple devices will tend to be more accurate because they can be calibrated to compensate for the mic in the device where as there are too many different devices in the Android market.

Pink noise is a signal that has equal power across each octave. In particular, you want a -20dBFS pink noise file. You can get these in a number of ways. One way may be to create it using a plug-in in your DAW or NLE. For example, in Pro Tools, you can use the Signal Generator plug-in, but you can also download a useful set of test/calibration files from Blue Sky, and on their site, they cover all the nitty gritty of monitor calibration in much more detail.

The advantage of using the bandwidth-limited signals in the Blue Sky folder is that they limit many of the room interaction effects often associated with measuring SPL and broadband pink noise, so my advice is that they are well worth using, especially if the acoustics of your space are not as good as you would like.

When you download the test files from Blue Sky, you get four files…

1. 1kHz file recorded at -20dBFS for electrical calibration

2. 40Hz to 80Hz bandwidth limited pink-noise file recorded at -20dBFS

3. 500Hz to 2500Hz bandwidth limited pink-noise file recorded at -20dBFS

4. Full-bandwidth pink-noise file recorded at – 20dBFS

These test files are all mono files. You need to hard assign them to the left and then the right. Don’t use a pan control, and don’t feed more than one channel at a time.

The reality of most setups these days is our reference is around -20dBFS, so there is little need to use the 1K reference tone. You can go straight to the 500 to 2.5kHz band-limited pink noise.

As my studio fits in the 40 to 140 cubic meter category, I am going to demonstrate how to calibrate your monitors to 78dBC SPL. If you are calibrating for other spaces, use the appropriate SPL target.

Set your main monitor control to an appropriate point. The exact position will depend on your system and whether you have active or passive speakers.

Set your SPL meter on a stand at eye height at the position in the room where you would be sitting. Effectively, it should occupy the space where your head should be. Rotate the spl meter so it is pointing at the left speaker.

Assign the 500-2.5kHz pink noise signal to just the left channel. Ensure nothing is coming from the right channel or any other channels.

Now, adjust the gain control on the monitor speaker so that the SPL meter reads 78dB. Repeat for each channel, but if you have a 5.1 monitor system, then repeat for the centre, right, left surround and right surround until all the channels have been calibrated. If you don’t have bass management, then you are done.

If you have bass management, then feed a 40-80Hz pink noise signal to the left channel only. Adjust the subwoofer level control until the subwoofer reads 78dBC (slow) at the mix position. The meter will bounce around a little, so you will need to do a mental average (I tend to filter out the peaks in my mind, so I don’t set the sub too hot). Check that when you feed the right channel with the 40-80Hz pink noise you get a similar result, all being well you shouldn’t need to make an adjustment.

There is also a speech sample from the ATSC, which you can download and playback. You should find that this speech sample should be at a comfortable volume when played back over a calibrated system.

Now, start mixing content on the principle that if it sounds too loud, it will be too loud, and if it sounds too quiet, it will be too quiet. However, if using your calibrated monitoring, you find that your mixes come out too loud, say 2LU high, then readjust your monitor calibration and bring the level up 2dB.

Continue mixing and see if that fixes the problem. The key point is to calibrate your monitors to suit you, not to a specific number.

What Next?

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.