More Pro Tools Mastering Tips

A meter or limiter that can display inter-sample peaks is highly desirable, as these will not show up on a conventional peak meter but can trigger distortion in lossy codecs such as those used by streaming services.

We continue our exploration of the mastering possibilities in Pro Tools.

In last month’s column (SOS February 2018), we looked at how you can set up a Pro Tools Session so as to carry out mastering duties, and we briefly discussed the sorts of processors that are needed to master in today’s environment. This month, I’m going to go into more detail about the processes involved in mastering and the tools that can help you implement them.

The exact make-up of the plug-ins you will need for mastering is dependent on the material you are mastering and what work needs to be done to it. You can start off with the stock plug-ins in Pro Tools, like the EQ3 and the Maxim limiter; specialist mastering plug-ins are also available, but there’s no reason not to use any plug-in if you like what it does. However, now that delivery formats have moved away from CD and towards loudness-normalised streaming services such as Spotify and Tidal, it is definitely worth having specialist tools available to help you manage levels appropriately. These include suitable metering tools and a limiter that has a ‘true peak’ option to contain inter-sample peaks: examples include the Avid Pro Limiter, Nugen Audio’s ISL (shown above) and the new Sonnox Oxford Limiter v2.

All Things Being Equalised

Sonnox Oxford Limiter v2.The EQ part of the mastering chain is a good starting point, for both enhancing the overall sound as well as fixing any problems that might be evident. Unless you have to fix a very specific problem, subtlety is the name of the game, so use low Q and cuts or boosts of no more than 3dB. If the track has been mixed on small monitors, you may need to look at the 150 to 250 Hz area; a gentle dip here is often required to remove muddiness that can build up. A boost at around 5kHz can help with vocal clarity, while a high-frequency shelving boost at around 15kHz is often described as ‘adding some air’ to the sound.

More intransigent frequency-balance problems, or issues that are only problematic intermittently, may require more sophisticated tools such as multiband compression or dynamic EQ. Examples include vocal sibilance, occasional over-prominent bass notes, and mid-range harshness in loud sections of the track. For more on these tools see SOS’s ‘DIY Mastering Made Easy’ article in the November 2017 issue (www.soundonsound.com/techniques/diy-mastering-made-easy).

Your limiter should be the last plug-in in the chain. In the days of CD, which is a peak-normalised format, limiters would be used along with other dynamics processors to make tracks as loud as possible, sometimes to the detriment of sound quality. However, with loudness normalisation becoming the norm, there is now no longer any advantage in making your track louder than the target value to which a playback system will turn it down. On a typical streaming service, a more dynamic mix that hits the target value will sound better than a heavily compressed one that exceeds the target value.

The ability to measure loudness in LUFS is vital when mastering for streaming services.This is where the aforementioned specialist metering plug-ins come in. To get the level of your mix right, you need not only a peak meter but also a loudness meter such as Nugen Audio’s MasterCheck Pro or Levels from Mastering The Mix that can give you a reading in LUFS. Short for Loudness Units Full Scale, this is a new unit of measurement designed to recreate the way our hearing perceives loudness. It’s also vital to have an output meter that can indicate inter-sample peaks. More and more music is being delivered using lossy codecs like AAC and MP3, and these codecs can distort easily when the reconstructed signal clips, even if individual samples do not reach peak level.

To guard against unexpected artifacts from these encode/decode cycles, plug-ins like the Sonnox Codec Toolbox, its bigger brother Sonnox Pro-Codec and MasterCheck Pro from Nugen Audio enable you to monitor through a lossy codec to make sure that the mastered track will sound as you want it to sound. For more on this area see our article 'Mastering For Streaming Services' in the SOS June 2017 issue (www.soundonsound.com/techniques/mastering-streaming-services).

Gaps & Levels

As we saw last month, those with powerful systems may be able to implement separate real-time plug-in chains on each track in the mastering session, but in other cases it may be necessary to render plug-in processing in order to conserve CPU cycles. Whichever technique you use, you will end up with a session with the tracks laid out in the album order. You can now use the normal Pro Tools editing and moving tools to set the gaps between the tracks and adjust the levels of the tracks so that the listener doesn’t have to adjust his or her volume control from track to track.

Back in the good old days, we would have to make these loudness judgments by spot-checking different parts of the different track and then making gain adjustments until we were happy with the subjective levels of each. Today’s loudness metering tools can help, by making it possible to measure the perceived loudness of each track and adjust the gain to compensate. To make this work effectively, you need to measure the average loudness of each track using the Integrated Loudness option, which will give you a measurement in LUFS. When adjusting the gain of each track, assume 1LU is equivalent to 1dB. If your ears disagree with the meters, trust your ears!

Once you have the relative loudness of the tracks settled, set the gaps between each track. To save having to re-select everything to the end each time you make a small adjustment, you can enable pre-roll in the Transport window; set it to around 20 seconds so that with any given track selected, you hear a good chunk of the preceding track and the gap, then the start of the selected track.

Make The CD

Pro Tools has all the features you need to edit and process master tracks, but it lacks the facility to burn CDs itself, or to export projects using the Disc Description Protocol (DDP) format that is widely used by pressing plants. This is perhaps less of a problem than it used to be, given that fewer projects are making it onto CD these days, but if you do need to master a CD you will need to install specialist software.

On the Windows platform both SADiE and Pyramix are obvious candidates, but in the Mac world we are somewhat limited. Possible candidates are Toast or, better still, check out HOFA CD-Burn.DDP.Master, which is a dedicated album software package from which you can burn CD masters or produce a DDP image file, which bypasses the error problems from mastering CDs from a CD. PreSonus’s cross-platform Studio One DAW also includes a dedicated mastering screen (the Project) with DDP export.