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Post Production Audio: Broadcast Limiters and Loudness Metering

Any time you’re working on a mix that’s going to broadcast, it’s important to ask for specs. Specs are essentially a set of rules for each broadcaster, such as:

Generally there will be a “spec sheet” for each broadcaster (i.e. ABC, CBS, BBC, etc) that your client will provide when asked. Spec sheets aren’t necessarily public or available online, but some are (such as NBC Universal). Some online content providers (like Amazon), movie theater chains, and movie distributors also have specs, so it’s always good to ask.

To understand some important concepts, we’ll take a look at PBS’s most recent specs (2016), found here.

For PBS, it’s a 21-page document that includes requirements for video, audio, how to deliver, file naming, closed captioning, etc. It gets pretty detailed, but it’s a good example of what a spec sheet looks like and the types of audio requirements that come up. The information in the spec sheet will dictate some details in your session, such as track layouts for 5.1, where your limiters should be set, dialog level, bars and tones, etc. We’ll break down a few of these important elements.

PBS Technical Operating Specification 2016 – Part 1, Page 6 Sections 4.4.1, 4.4.2 – Audio Loudness Requirements

The three most important details to look for on a spec sheet are peak loudness, average loudness, and the ITU BS 1770 algorithm. These will be explained in detail below. In this case, the PBS specs are:

Peak Loudness: -2dBTP (“true peak” or 2 dB below full scale). This is your brickwall limiter on the master buss/output of the mix. In this case, it would be set to -2dB.

Average Loudness: – 24dB LKFS +/-2 LU.

ITU BS 1770 Algorithm: ITU-R BS.1770-3. This is the algorithm used to measure average loudness.

Some background on the average loudness spec:

Before 2012, there used to only be one loudness spec: peak loudness. This was a brickwall limiter placed at the end of the chain. Back then, most television networks (in North America) had a peak level of -10dBfs. From the outside (especially coming from the music world) it seems like an odd way to mix – basically you’ve got 10 dB of empty headroom that you’re not allowed to use.

As long as your mix was limited at -10dB, it would pass QC even if it was squashed and sounded horrible. That’s what was happening, though, especially with commercials that were competing to be the loudest on the air. If you remember running for the remote every commercial break because they were uncomfortably louder, that was the issue.

In the US, Congress enacted the CALM act which went into effect in 2012 and required broadcasters to reign in these differences in loudness between programs and commercials. The spec that evolved from this was average loudness level. A loudness measurement covers the length of the entire piece, whether it’s a 30 second spot or a 2 hour movie. Average loudness is measured through a loudness meter. Popular measurement plugins are Dolby Media Meters, Izotope Insight and Waves WLM.

Izotope Insight screenshot

The ITU developed an algorithm (ITU BS 1770) to calculate average loudness. The latest algorithm is 1770-4 (as of early 2017). To get technical, loudness is an LEQ reading using a K-weighting and full-scale; the designation for this reading is “dB LKFS”. In the PBS spec sheet, section 4.4.1 and 4.4.2 say mixes should use ITU BS 1770-3, which is an older algorithm. This is an important detail, though, because when you’re measuring your mix, the plugin has to be set to the correct algorithm or the reading may be off. The PBS specs were written in 2016 (before 1770-4 came out). Broadcasters update these every couple of years, especially as technology changes.

In this PBS spec, the optimal average loudness is -24dB LKFS, but there is an acceptable loudness range (LRA) above and below +/-2 LU (“Loudness Units”). Basically that means your average loudness measurement can fall on or between -26dB LKFS and -22dB LKFS, but ideally you want to mix to hit at -24dB LKFS. The measurement plugin will probably show a short term and a long term value. The short term reading may jump all over the place (including beyond your in-spec numbers). The overall (long) reading is the important one. If the overall reading is out of range, it’s out of spec, won’t pass QC and will likely be rejected for air. Or, it may hit air with an additional broadcast limiter than squashes the mix (and doesn’t sound good).

As HD television has become more popular, broadcasters have loosened up on the peak loudness range. PBS is pretty liberal with -2dBTP (or -2dBfs); some broadcasters are at -6dBfs and occasionally some are still at -10dBfs.

Below is a screenshot of a mix with a limiter at -10dBfs (you can see the compression – it doesn’t sound very good!) and the same mix without. If your average loudness reading is too hot and your mix looks like the upper, there’s a good chance that your mix (or dialog) is overcompressed!

Initially re-recording mixers thought loudness metering would be restrictive. Average loudness is measured across the entire program, so there’s still room for some dynamic range short term. Loudness specs can be a problem for certain content, though. For example, you’re mixing a show with a cheering audience that’s still being picked up as dialog by the loudness meter. Say your spec is -24dB LKFS (+/-2). You mix the show host at -24dB LKFS (in spec) but every time the audience cheers the short term measurement is -14dB LKFS. The overall loudness measurement might be -18dB LKFS – which is way out of spec! So sometimes you end up mixing dialog on the low side or bringing down an audience more than feels natural to fall in spec.

Another difficulty of mixing with a loudness spec is making adjustments when your overall measurement is out of spec. A dB of LU (the unit of measurement for average loudness) is not the same as 1dBFS (full scale). If you drop the mix 1dB by volume automation, it’s not necessarily a 1dB change in average loudness. If you’re mixing a 30 second promo and the loudness level is out of spec it’s easy to adjust and recheck. If you’re mixing a 90 minute film, it takes a bit more work to finesse and time to get a new measurement.

There’s software that will make these adjustments for you – basically you can tell the software what the specs are and it’ll make small adjustments so the mix will fall in spec. While this is a good tool to have in the toolbox, I encourage mixers to first learn how to adjust their mix by hand and ear to understand how loudness measurements and metering works.

I find in general if dialog is sitting between -10 and -20dBfs (instantaneous highs and lows) and not over-compressed, the average loudness reading should fall pretty close to -24dB LKFS. When I first started mixing to an average loudness spec, my mixes were often averaging hot (-20 to -22dB LKFS) when spec was -24. My ear had become accustomed to the sound of compressed dialog hitting a limiter on the master buss. What I’ve learned is that if you’re mixing with your dialog close to -24 dB LKFS (or -27 for film) you can bypass the master limiter and it should sound pretty seamless when you put it back in. If you’re noticing a big sound change with the limiter in, the overall reading will probably fall on the hot side.

When I start a mix, I usually dial in my dialog with a loudness meter visible. I’ll pick a scene or a character and set my channel strip (compressor, EQ, de-esser, noise reduction etc) so the dialog mix lands right on -24dB LKFS. I do this to “dial in” my ear to that loudness. It then acts as a reference, essentially.

One thing I like about mixing with a loudness spec is you don’t have to mix at 82 or 85 dB. While a room is optimally tuned for these levels, I personally don’t always listen this loud (especially if it’s just me/no client or I anticipate a long mixing day). Having a loudness meter helps when jumping between reference monitors or playing back through a television, too. I can set the TV to whatever level is comfortable and know that my mix is still in spec. When I’m mixing in an unfamiliar room, seeing the average loudness reading helps me acclimate, too.

I mix most projects to some sort of spec, even if the client says there are no specs. Indie films, I usually mix at -27dB LKFS and a limiter set to -2dBFS or -6dBFS (depending on the content). If an indie film gets picked up for distribution, the distributor may provide specs. Sometimes film festivals have specs that differ from the distributor, too. If you’ve already mixed with general specs in mind, it may not need adjusting down the road, or at least you will have a much better idea how much you’ll need to adjust to be in spec.

Andrea Bocelli at Arena Da Baixada – Curitiba

I’m not sure if everybody had, at least once in life, the same feelings I had as a teenager: “Will I ever be a professional? Will anyone pay me for my work someday? Will someone ever trust me?” I have quite a clear memory of all these feelings.

I’m not sure about when this all changed, it was a smooth transition from being a student to trainee, a “rookie” technician and 15 years later here we are: huge concerts, immense responsibilities, overnights, difficult problems to solve. Andrea Bocelli world tour comes to Brazil again, and we are in a stadium at Curitiba. Brazilian rental company Loudness was the audio contractor, providing a massive L’Acoustics system for this concert. Loudness has done several Bocelli’s concerts over the years, always providing the best equipment and human resources. Our friends from Bocelli’s audio crew are true professionals, always trying to find the best solutions for each venue, and it’s always a challenge to set up their sound systems.

Fernanda and Marzia

This time I had the opportunity to bring a friend, hard-working girl Marzia Brini, who I met working for the Rio 2016 Olympic Games. It was the perfect event to bring her to our team, and she is Italian. It is always nice to have someone that speaks the native language of our clients; it can make a big difference. Marzia did great. It was also one of the few times I was not the only woman on the team – and it was awesome!

As usual, we had a massive system to set up in a very short time.  The stadium was enormous and very reflective, the sound design was about having more sources, less level and avoiding reflections as much as possible. Some numbers around this concert at Arena da Baixada / Curitiba / Brazil: (L’Acoustics) 64 K1, 48 SB28, 64 KARA, 16 V-DOSC, 50 KUDO, 24 12XT, 108 LA-8 amplifiers, plus analog boards Midas XL4 x2 and XL3.

It was not easy, but we did it! As the show started, I had these memories from my teenage years and all the doubts about my future, and suddenly I felt very proud. I felt proud about the choices I had made, some good and some not so good, but everything made up the path to get to where I am.  The feeling of being part of a team and accomplishment, to make your client happy, to make the show happen. That feeling!

End of the concert: load out was ten hours of nonstop heavy work, but again it has to be done. Thanks, Marzia and the Loudness crew, I hope to have many more successful shows and hope to see more and more women working on event production.


Fernanda Lemos is the only woman working as a sound engineer for Loudness, the second largest sound company in Brazil. Fernanda has faced obstacles and some of them are cultural, as her job in Brazil is viewed as man’s work. Some of artists automatically won’t work with her as they do not believe a woman is capable of doing the job. In the beginning, she thought this would change by showing she was capable of doing the job. She has come to realize it is going to take much more time and societal norms must change. She is proud that she is a part of making the change happen.

Breaking Down Doors in Brazil

Thirteen years ago Fernanda Lemos was a musician in a rock band; today she is the only woman working as a sound engineer for Loudness, the second largest sound company in Brazil. Loudness was founded in 1976 and has become the premier production company in Brazil, providing sound for international touring artists such as Rush and Bon Jovi, Broadway productions and events. How does one go from being a musician to being the only female sound engineer for the one of the largest sound providers in Brazil?

The Audio Team of Loudness

The Audio Team of Loudness

It all started back when she was a keyboard player in a band without anyone to run sound. So Fernanda started mixing their sound checks, and at the same time, she was learning how to record. She read a lot about acoustics, audio, and started following the Brazilian band Paralama do Sucesso. She went to every show she could and tried to get into the sound checks. Paralam do Sucesso had the best audio technology, and she got to be there, watching, listening, and asking about everything. At some point, she decided to leave the stage for backstage.

Fernanda enrolled in an audio course with Brazilian sound engineer Carlos Roberto Pedruzzi. A year later she enrolled at the Estacio de Sa University, in Rio de Janeiro. The university offered a bachelor’s degree in a program called Music Production and Recording, directed by Brazilian music producer Mayrton Bahia. As luck would have it, one of the instructors owned a small sound company and gave Fernanda her first job.

Fernanda started as an assistant sound tech at a small theatre. There she started mixing monitors and FOH. The pay was low, but what Fernanda gained in experience and confidence made up for it. She eventually started working outside shows with Sigmatec and then was referred by her first audio instructor, Mr. Pedruzzi to be a trainee at Loudness.

At Loudness she does a bit of everything depending on the gig, although she works mainly as a monitor engineer or monitor tech. She has been the monitor engineer for Brazilian artist Rita Ribeiro for the last five years. Fernanda is also able to work alongside her husband, a sound engineer at Loudness, he usually takes care of FOH, while Fernanda takes care of the stage. She says they are known as the Audio Couple. She has been able to take part in additional training and certification seminars with Meyer Sound, Digico, Pro Tools, K1 and V-Dosc, and Smaart. She is fluent in English which is an asset when working with international artists.

Rush

Rush

Fernanda recalls one of the most significant and important shows she has done as a lead tech. The shows were Andrea Bocelli at Belo Horizonte, and São Paulo. Andrea Bocelli concerts are quite challenging as their sound crew is very meticulous. The shows are usually staged in expansive areas, with a significant amount of equipment. The Belo Horizonte concert was especially difficult as they only had one night to set up. It was staged on a busy avenue that had to be closed down. “We had to set up the delay towers in the middle of the traffic! The Bocelli crew are great people and superb professionals, so we were able to pull it off. Every time I work with the Bocelli crew I learn something”.

Andrea Bocelli K1 setup at Buenos Aires, Argentina.

Andrea Bocelli K1 setup at Buenos Aires, Argentina.

Loudness provides live recording services for many of the most prominent artists in Brazil. Fernanda often takes care of the recording unit, setup and operates Pro-Tools when it’s needed. “We have two main live recording sets, one fully digital with Avid D-Show/Profile as preamps, other with Amek Recall by Rupert Neve consoles, which sounds amazing! All were recorded with 2 Pro-Tools 10 (HD 3)”. When she was in school, she worked at the university’s recording studio, and this was the beginning of digital audio in Brazil, with Yamaha’s digital consoles like 02-R. The studio had one, and a Pro-Tools 24 mix plus. Because it wasn’t very reliable at this time, they were still using ADAT recorders. This gave her the opportunity to start and continue using recording systems.

Fernanda has faced obstacles, and some of them are cultural, as her job in Brazil is viewed as man’s work. Some of the artists automatically won’t work with her as they do not believe a woman is capable of doing the job. In the beginning, she thought this would change by showing she was capable of doing the job. She has come to realize it is going to take much more time and societal norms must change. She is proud that she is a part of making the change happen.

Fernanda offers this advice to young women entering the field –

Don’t be afraid and don’t be mad if everybody is watching you and testing you all the time. Do your job the best you can and don’t be scared to make mistakes and ask questions. Do the best you can and do not give up!

Must have Skills:

I believe a musical talent helps a lot when dealing with musicians, I’ve been in their position before, and I know how it feels. It makes it a lot easier to communicate with the artists. Listen to all kinds of music.

Being able to remain calm when dealing with problems is crucial.

Being organized.

Favorite Gear

I love huge PA systems that sound smooth and great, even at long distances. I love big concerts!!! The first big PA I worked with was a Meyer Sound M3D, and I remember very well how delighted I was. I know it’s heavy and not the easiest to set up, but I still like the way it sounds. The L’Acoustics V-Dosc is kind of a dream sound, you just set up and it’s ready! K1 has made our lives so much easier, it sounds incredible in all situations, from heavy metal to Andrea Bocelli. I love analogue desks; I’m quite sad that I entered the audio world at the “end” of these great-sounding technologies. My preferred one is surely the Midas XL4! I have done a lot of jobs only setting it up for other people ” I did not get to really “put hands on it,” but my first time mixing with one was delicious! I’m not an anti-digital person, nowadays I like a lot to use Digico desks like the SD8, and I think they sound really great! But if I had a choice for touring… big heavy Midas, no doubt”!

Favorite things about touring

I always loved to travel, and I hate routines that never change. Mix it all together, and I found the perfect job. I never get tired because we are always moving and have new challenges. I love to meet people from all over the world. I like planes and airports, and I love hotels too! I get bored when I am at home too long.

Least Favorite

In fact, being a lady in this area has some problems… for me, WC is the major problem! Very often the sites and venues have only WC for men, and they tend to be dirty. When my husband and I are on different gigs, and we keep missing each other.

Favorite Day Off Activity

I sleep and then I like to discover new places -like beaches, excellent restaurants, taste local beers and regional food…

Long-Term Goals:

I’m pleased to be where I am now. I really want to keep learning. My dream is to do at least one big world tour. My husband and I are thinking about moving to the USA for a couple of years to study and work.

Of course, I would love to work with other women. In Brazil, we only have a few women working with sound, especially live sound. We have a group on Facebook, the “Female Pro Audio,” in which we share with other women our experiences, job opportunities, and talk about sound! I hope it will inspire more and more women and girls to join our “sound world,” and help them overcome the barriers all newbies have. Being a woman makes it doubly difficult. We can always help each other.

The best part of my job is at showtime looking at all the people who are so happy and to think I am a part of this. It’s just amazing.

jazzOP

 

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