Clients always want a mix with impact. In their minds, impact equals loud, but that’s not really true. What you really want is a dynamic mix that fits within a comfortable range. The listener should hear some variance without the broadcasters and/or streaming platforms affecting the mix too badly through loudness normalization. Hence, the battle over loudness and in recent times, the various ways to measure it.
In the early 2000s the so-called loudness wars came to the attention of legislators who, through the FCC, eventually codified US standards with the CALM Act of 2010. This resulted in loudness targets measured in LUFS (loudness units full scale). It has become the standard for broadcast mixers ever since. However, years before the CALM Act, noted mastering engineer Bob Katz offered a solution in a white paper to the AES. His proposal was the K-scale, which is still a valid way to mix and is an available feature in a number of metering plug-ins. This method is known to recording engineers, but probably something that most video editors never knew existed.
The K-scale is based on the concept that mixing should always be done at a reference speaker volume. Based on research done by Tomlinson Holman (the TH in Lucasfilm THX) and Dolby for theater sound calibration, that level is 85 dB SPL (sound pressure level) in movie theaters. The K-scale weights a VU meter’s scale according to three levels of headroom. These are labelled as K-12, K-14, and K-20 for 12, 14, and 20 dB of headroom, respectively. K-20 is intended for mixes with a wide dynamic range like classical music, K-14 is good for pop music, and K-12 for broadcast. Of course, those genres are only suggestions.
The point is to preserve dynamic range in the mix based on the type of material. The key to the weighting of the scale is that 0 VU always equates to a speaker volume of 85 dB SPL. It’s intended for professional music mixing and mastering studios. However, don’t discount its value for modern video post. K-scale metering has two advantages. First, you are mixing with a VU style meter, which has an averaged response. That is more akin to how humans perceive loudness than fast-responding full scale meters common to most NLEs and DAWs. Second, it encourages consistent monitoring levels when you mix audio.
How do you implement this in a small edit suite?
First, set up the room properly if possible – depending on available space. Place your speakers at the front. Your seating location should be about 1/3 of the way from the front with 2/3 of the room space behind you. Sound absorption panels are highly recommended. The speakers should be about five feet from you. Calibrate your speaker volume using a sound pressure level meter. The simplest and cheapest option is a phone app. I use the free NIOSH SLM app on my iPhone set to C weighing. It’s fine for casual monitoring like this, but understand that a phone app is not accurate in critical environments due to how the built-in mic is calibrated.
There are several meter plug-ins that feature K-scale presets. I prefer the free mvMeter2 from TBProAudio, which emulates an analog VU meter. It includes numerous VU and PPM presets along with the three K-scale settings. Place this on your final master or mix bus without any other effects or level changes after the meter. Play a pink noise file in your timeline and set the output level so that it reads 0 VU on the meter scale that you’ve picked – for instance, 0 VU on the K-14 scale.
There are plenty of home theater guides about how far away you should be when measuring SPL. The official distance would be one meter from the speaker, but it’s also valid to measure from where you would normally sit. A comfortable listening volume is going to be somewhere between 70 and 85 dB SPL. Start at 85dB. Test your mix playback. If this sounds too loud, you can lower the level and retest with the pink noise file. You might not operate at that level the entire time that you are editing. However, keeping this consistent level each time you mix will give you more predictable and translatable results.
Using this system to mix
Now, let’s put this into practice. Most of the mixes I do myself are for broadcast TV or some social media outlet, like YouTube. Each uses different loudness targets. I find that the K-12 or K-14 setting is best for my internet work and K-20 is best for broadcast. Note that Katz recommended the K-12 scale for broadcast; however, that was before the industry standardized at -23 or -24 LUFS. I find that if you use the K-20 scale (with 20 dB of headroom) that the result is closer to this spec. That difference is probably because Katz was talking about music broadcast, as in radio airplay of songs, rather than TV programs.
The reading on the meter will react like a typical, analog-style VU meter. If you’ve mixed with VU meters in the past, then you’re probably used to the needle hovering around 0 VU and safely (and often) bouncing up into the red overload zone up to +3 dB or more. When using the K-scale method, you’ll find that a lower meter reading will actually match what sounds right to you, assuming you followed the speaker calibration described above. Most of the time my levels are somewhere in the middle of the VU meter, well under 0 VU. It only bounces above 0 on a few peaks. If you compare this to Premiere Pro’s loudness meter, you’ll find that this equates to around -20 to -14 LUFS, which is a good target for platforms like YouTube.
Remember that a VU-style meter is an average. Be sure to limit your signal for peaks. A limiter plug-in should be placed before the meter. In my work that’s usually set to a brick wall level of -3 or -6 dB true peak depending on the program. This is lower than the -1 dB limit often recommended for music mixes. This approach to mixing should give you a decent amount of dynamic range without the need for severe normalization by the platforms.
It’s important to understand that many of these recommendations for streaming service targets are based on music mixing and not TV shows and films, where dialogue is usually dominant. In 2021 the AES posted an updated technical document (linked here) that spells out recommendations for dialogue-based content. Their suggested target is -18 LUFS based on measuring the dialogue tracks rather than the full mix.
The K-scale system is old, though still valid. Of course, NLEs like Premiere Pro and Resolve include their own loudness meters and there are numerous third-party plug-ins using traditional and modernized ways to measure loudness. One modern metering technique is to measure the difference between peaks and short term loudness, aka PSR, and/or peaks versus long-term loudness, aka PLR. A plug-in like Meterplugs’ Dynameter provides you with this feedback. The reading will tell you how the mix level will be handled by the loudness management of the top streamers. Loudness Penalty is an online resource that will tell you this, as well.
Lastly, what about headphone mixing? There are pros and cons, but in order to trust your ears and know whether your mix will translate to various speaker systems, Waves has a solution. Their Nx technology emulates the three-dimensional sound and space of several famed studio control rooms, including those of Chris Lord-Alge, Ocean Way, and Abbey Road.
Place the plug-in last in your mix bus, select the correct headphone or ear bud model EQ curve (270 presets are available), and you’ll experience your mix based on an emulation of those speaker systems and rooms. Each plug-in includes head tracking and Waves sells a separate Nx tracking sensor. However, it can also use your front-facing computer camera.
With the plug-in enabled, you’ll hear a proper sound image as if listening to those speakers (Abbey Road, Ocean Way, etc.) instead of the usual left/right split of headphones. With head tracking, the spatial image shifts as you move your head. If you disable head tracking, you can still manually pan the image around the room and hear the result in your headphones. Since the plug-in is only designed for headphone monitoring, disable it when listening on external speakers and when you output the mix. Since the plug-in is manipulating phase to create these emulations, material that is truly just mono might sound more odd than full stereo mixes.
Granted, you’ll probably never own the kind of speaker systems these studios use, but the real point is that these plug-ins give you a transportable reference based on some of the best control room environments. As you move between different systems with different monitor set-ups, you can maintain a common monitoring reference for all of your mixes.
©2023 Oliver Peters
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