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What Do Mastering Engineers Actually Do?

VIDEO By Sam Inglis
Published February 2021

Mastering is a job that is widely misunderstood and misrepresented. Can it really turn lead into musical gold? Or is it just a waste of money? 

There are lots of jobs in the music industry that no-one understands, and mine is one of them. I mean, some people think I actually sit around all day playing with expensive bits of music equipment and then occasionally jotting down a review. Imagine.

But I think one of the most misunderstood jobs in audio is that of the mastering engineer.

So what do mastering engineers actually do and why do we need them?

Well, let’s start with a bit of history...

Back in the day, music would be recorded on one medium and released on a different medium. You’d track your album to two-inch tape. You’d mix it to quarter-inch or half-inch tape, but it would be released on vinyl, or cassette, or compact disc, or eight-track cartridge. And the job of the mastering engineer was to handle that transfer from the recording format to the delivery format.

That required specialist equipment and expertise — especially when you’re cutting vinyl. The mastering made a huge difference to how good the resulting record would sound. I don’t think good mastering ever made anything a hit, but I’m pretty sure that bad mastering could stop something from being a hit. Really really bad mastering would mean no-one could actually play your song to find out if it was any good.

Sometimes, mastering engineers had to apply processing in order to transfer audio from tape to vinyl. Too much low bass, or excessive sibilance, or things that were out of phase could make it impossible to cut a record. The dynamic range of the tape recording might be too wide to fit onto vinyl or cassette. So mastering studios contained equalisers and de-essers and compressors and limiters. And ashtrays and brown corduroy sofas, because this was the seventies.

However, it wasn’t the job of the mastering engineer to improve the sound. The challenge was to retain the quality of the original recording as much as possible, which was no mean feat when you were going to vinyl or cassette. If you as the mixing engineer or the producer heard the finished album and it even came close to matching the original tapes, you’d be pretty happy.

Fast-forward to the 21st Century, and we record and mix audio to digital files on a computer. We release our music as digital files on a computer. If we’re feeling particularly retro we might put those digital files onto a CD and get some physical copies made. It’s not quite idiot-proof, but with a bit of common sense you can do all this yourself. Getting music into a release format doesn’t require the services of an expensive professional any more.

But we still have expensive professionals. So what’s happened?

Why do we still have Mastering Engineers if you can do all this at home?

Three reasons really. First of all, there is still a sense in which mastering engineers make our music ready for release. We don’t have to worry about whether the vinyl disc will actually play without skipping, but it is still important that music is optimised for particular playback media. And in this day and age, that means streaming.

A good mastering engineer will know how to hit the 'sweet spot' where your tracks are exactly loud enough to sound at their best on Spotify or YouTube without getting turned down. They’ll be able to pick up red flags like inter-sample peaks that could make your tracks sound distorted on streaming services. And yes you could learn to do this stuff yourself, but sometimes it’s more efficient and more reassuring to hire an expert to do it for you.

Secondly, a mastering engineer will be able to ensure that your music translates well. What does that mean? Well, a lot of us are working in home studios that aren’t acoustically perfect. Maybe we’re even mixing on headphones. There’s no guarantee that a mix that sounds good here will sound good on all playback systems.

A good mastering engineer will be able to identify things about your music that might not sound so good on other systems. Maybe that sub-bass is a bit too prominent on a full-range system or not audible at all on small speakers. Maybe your piano is out of phase and disappears in mono. Maybe there’s some distortion that you haven’t noticed, or someone has snuck in and overdubbed a banjo when you weren’t paying attention.

Good mastering can catch all these things, and fix most of them.

Another thing that a good human mastering engineer can do is take a sequence of tracks and make them sound like a coherent whole. I’m sure we’ve all had the experience where each track we make sounds OK on its own, but when you put them in a running order they just don’t seem to flow sonically, and you end up chasing your tail cutting bass from track 2 so it sounds more like track 1, turning down track 3 so it matches track 2 and so on. That’s something mastering engineers are really good at.

In other words, a human mastering engineer is a safety net. They are a fresh pair of ears who can listen to your music on a really good reference monitoring system, identify potential problems with it, and help you get your project ready for release.

Should you use a Mastering Engineer?

It’s definitely worth using a good mastering engineer if you can afford it, if only for peace of mind. But if you can’t, there’s also now a big industry of home mastering products: special plug-ins with lots of different processing modules, and AI-based online processes that will master our music automatically. Can mastering plug-ins really take the place of a human mastering engineer?

The short answer to that question is ‘no’, and to understand the reasons why, let’s consider what mastering engineers don’t do. In my experience, they don’t use stereo image wideners, matching equalisers, exciters, microphone modellers or tape emulators. They almost never use multiband processing. They don’t add reverb or delay. Quite often they don’t even use EQ or compression, and when they do, they’re applying half a dB here and half a dB there.

When mastering plug-ins started to appear 20 years ago, they were designed to let you do the same sorts of thing. They had a simple EQ, a simple compressor, a simple limiter, and some utilities like dithering algorithms. But then they got into an arms race. Company X adds a three-band compressor, Company Y adds a four-band compressor. Someone on a forum says ‘I can’t get my mixes to sound as wide as Spike Stent’s mixes’ and Company Z think 'a-ha, we could add a widening module!'. And we as the consumers think Product A is obviously better than Product B because it’s got 43 processing modules instead of just 37.

So now, if you buy a mastering plug-in, you’ll find tens or hundreds of processing modules that a human mastering engineer would never use. And you’ll find presets that change your sound way more than a human mastering engineer ever would. These products won’t listen to your mix and explain that maybe you need to go away and turn the bass down. But they will widen it and compress it and EQ it and saturate it and apply lots of parallel processing or whatever happens to be fashionable at the time.

These products are not a safety net. They won’t save you from yourself in the way that a human mix engineer can. But what they do offer is a million ways to change your mix as part of the creative process. So by all means try out the presets in your mastering plug-in. Widen your tracks, distort them, add top end, compress them, de-ess them, process them in parallel. As Joe Meek said all those years ago, if it sounds right, it is right. But in my view, you should think of what you’re doing as part of mixing, not mastering.

One of the most valuable things that a human mastering engineer can do to your music is nothing at all. If your mix sounds right as it is, a good mastering engineer won’t change anything. And that’s something you won’t find as a preset in any mastering plug-in!

And here's the series of video tutorials that Sam refers to:

Mastering Essentials: The SOS Techniques Guide