Mastering In Your Daw

Let’s get one thing out the way: There’s mastering and there’s MASTERING. MASTERING, as in this is a crucial CD for your band, you’re going to duplicate 1,000 copies, you want to blow people away when they hear it (“you only get one chance to make a first impression”), and you don’t want any mistakes. This is when you call in the professional who has done this dance a zillion times before, and will squeeze every last bit of musicality out of your creation. Yeah, you’ll pay — but hopefully, when you look back (and assuming you chose the right mastering engineer, which is a whole other issue), you’ll think it’s the smartest move you ever made.
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But then there’s mastering, with a small “m”. It’s the demo that the band listens to when deciding the song order, the live recording that gets sold at gigs, the 30-second spot for Mighty Dave’s Kool Kar dealership, and the narration for the kiosk video done by one of your regular clients. You’re not going to hop on the first plane to Maine and beg Bob Ludwig to do the mastering, so you decide to master it yourself. But do you really need a separate digital audio editor with a bunch of pricey plug-ins, or have DAWs progressed to where you can do it all without leaving your favorite host software?

First off, 95 percent of mastering is not in the tools but in the ears. If you have good ears, you can probably convince your DAW to do a decent job of mastering. Granted, most project studio, computer-based mastering is done with specialized digital audio editing programs (Adobe Audition, BIAS Peak, i3 DSP-Quattro, Magix Sequoia, Sony Sound Forge, Steinberg Wavelab, etc.). They offer deep navigation facilities, the ability to zoom in on waveforms, pencil tools to draw out clicks, and include mastering-oriented plug-ins. However, if your mastering needs aren’t too demanding, there are several ways to master using conventional multitrack recording programs. Interestingly, some can even do tricks conventional digital audio editors can’t do.

MIXING FOR MASTERING

There are several steps you can take while mixing to make for easier mastering. You should do these whether you plan to master material yourself, or hand your project to a mastering engineer.

-Always mix with the highest resolution possible — don’t downsample or do bit reduction (dithering) until the very end.

-Add any fade-ins or fade-outs during the mastering process, as you’ll have a better sense of the ideal fade time as you do the mastering.

-Don’t trim out all the “air” at the beginning of a tune. A clean sample of this may be essential if you need to apply any subsequent noise reduction or other audio restoration process, as the sample of hiss, hum, or whatever can be loaded into a noise reduction program that mathematically subtracts the noise from the track. Besides, sometimes you don’t want too abrupt a transition between dead silence and the beginning of a track.

-Don’t add any processing to the overall mix, just to individual channels — processing completed mixes is best left for mastering.

As you mix, watch closely for distortion. A few “overs” may not be audible as you listen to the mix, but may be accented if you add EQ or limiting while mastering. It’s better to concede a few dB of headroom rather than risk distortion.

-Roll off low frequencies in tracks that don’t have any low frequency energy. You don’t want any subsonic signals to work their way into a mix or a final master recording.

-Don’t normalize any of your mixes, as that means another stage of DSP (which may degrade the sound); and you may need to change the overall level anyway when assembling all the mixes into a finished album.

-Always make copies of your original mixed, high-resolution files prior to mastering. If the song is later remastered for DVD-Audio, included in a compilation, or used in any other context, you’ll want a mix that’s as easy to remaster as possible.

“REALTIME” MASTERING WITH A MULTITRACK PROJECT

A major difference with mastering in a host program is that you have the option to adjust mastering processors (which affect the final mixed output) as you mix. With digital audio editors, you are always working off-line with a previously mixed file. However, there are advantages and disadvantages to both methods. The process of mixing is daunting enough without throwing mastering into the equation; still, mastering while you mix means you know exactly what the final version will sound like.

Another consideration is that many people feel that separating the mixing and mastering process is beneficial to both, as they are different disciplines. You might want to “sleep on your mix” before mastering it.

If you decide to master as you mix, you’ll be inserting mastering processors in buses. This is because when you create a non-surround multitrack project, eventually all the tracks are going to dump through a mixer into a master stereo output bus. As with individual channels, buses have provisions for adding plug-in effects. How effects are accommodated depends on the program; for example, with Sonar the buses have standard effects slots, just like tracks. But Cubase SX has a few extra touches — both pre- and post-fader/post-EQ slots for effects, as well as excellent dithering algorithms for doing bit reduction (Figure 1). Note that Cubase SX has two post-fader insert slots, while Cubase SL has one.

If a program doesn’t include a post-level control effects slot, try feeding one bus into another. Insert the effect that should be post-level control into the second bus, and leave the second bus output level control at 0. Control overall level at the output of the first bus.

Once any effects have been added and edited as desired, you have three main options to create a mastered file:

-Export the track (also called bounce or render) to hard disk. This reads the final mixed output signal, including the results of any effects you’ve added, and writes the file to hard disk. Note that it still needs to be assembled with other tracks to create a complete CD.

-Send the output to a stand-alone CD or DAT recorder. This will record the final, mastered song, although again, you’ll still need to assemble these.

-Send the output through analog mastering processors, record their outputs into two empty tracks in your multitrack, then export those tracks to your hard disk.

A different technique is a compromise between mastering as you mix and mastering offline. After hearing a mastered song, you’ll sometimes wish you had mixed the song a little differently. For example, the mastering engineer might add some compression that subtly changes the mix, requiring you to go back and do a quick remix (let’s hear it for mix automation).

So, to create a more “mastering-friendly” mix, consider adding some multiband compression and overall EQ (usually a little more high end “air” and some tweaks in the bass) in the master bus to create a more “mastered” sound. Mix the tune while monitoring through these processors. Then, when you render or otherwise save the file, bypass the master effects you used. This results in a raw mix you can master in a separate program, or give to a mastering engineer, who anticipates the use of mastering processors but doesn’t incorporate their effects in the file. Should you do this, you may need to tweak the overall level when you remove the processors.

MASTERING INDIVIDUAL TUNES IN A DAW

Mastering a multitrack project in real time is a fairly new technique that’s definitely not for everyone. So, let’s look at two approaches to mastering that use the DAW more like a standard digital audio editor. (Note that Adobe Audition and Magix Samplitude/Sequoia are combination multitrack hosts/editors that are intended to do mastering as well as multitrack recording.)

The more “old school” approach is to take each tune, master it, save it as a stereo (or surround) file as a separate operation, then assemble all the tunes into a cohesive whole. A newer approach is to assemble all the tunes in a workstation (e.g. Sonic Solutions), and apply any processing, level changes, etc. on a more global level. Basically, this combines both mastering and assembly as one operation. Let’s look at the individual song approach first.

Open up a new file in your DAW, and import the mix into a track. If you need to process the right and left channels independently (e.g. there’s an instrument in the left channel that has excessive treble, and you want to EQ just that channel a bit without processing the right channel), then separate the stereo file into two mono files. Most software will let you do this as part of any “bounce to track” function. You may also be able to bring a stereo file into two tracks, use the balance control to separate the left and right tracks, then recombine them.

Here are some of the editing operations you might want to do:

Reduce peaks using automation envelopes. If some peaks are significantly louder then the rest of the material, this reduces the chance to have a higher average level, as the peaks use up much of the headroom. One solution is to add limiting, but another option that can affect the sound less is to use an automation envelope to reduce the levels of just those peaks. If the automation works on just a few cycles of the waveform, you probably won’t hear any difference compared to not reducing that peak; but once the major peaks are reduced, you’ll be able to raise the overall level. (And if you do add any compression, it won’t have to work as hard.)

Add dynamics processing. Generally, you’ll use a dynamics plug-in for the track holding the file, or possibly for the bus it feeds. Multiband dynamics processors are your best option; compared to standard compressors, they’re more transparent because dynamics control in one frequency band doesn’t affect other frequency bands (Figure 2). However, some people like slamming a stereo compressor because they can hear some “pumping” and “breathing,” which can give more of a vintage sound.

Another popular option is a loudness maximizer plug-in. This type of processor can greatly increase the overall average level, producing a “hot” sound. These plug-ins are often overused on today’s recordings, which creates distortion and degrades definition. I advise increasing the amount of maximization until you can hear the effect working. Then reduce the amount so you don’t hear it working. Eventually you’ll find a “sweet spot” between retaining good dynamics and increasing overall loudness.

No matter what form of dynamics control you use, it will affect the mix by reducing peaks and bringing up lower level sounds. This is equivalent to having a more “even” mix, and might be desirable. But if the mix ends up sounding too uniform, reduce the amount of maximization. Peaks and valleys are essential to a satisfying listening experience. A really “loud” cut may seem impressive at first, but is fatiguing after a short period of time.

Add EQ. For mastering, you’ll hopefully be dealing in broad strokes — a mild bass cut, or a little high-end lift — because any serious response issues were dealt with during the mix. This is why many older equalizers, like the Pultec, are favored for mastering; they have a subtle, yet pleasing, effect on the sound. Plug-ins like PSP’s MasterQ (Figure 3) and the UAD’s Pultec emulation fulfill this role in software.

If significant EQ problems exist, like large midrange or low-end peaks, you’ll likely need to plug in a full-blown parametric EQ, and tweak out the individual problems.

Your DAW probably includes EQ, but be careful about using it. The DAW’s EQs were likely optimized so you can open lots of instances at the same time, which means they can’t get too nuts about consuming CPU power. “Mastering oriented” plug-ins tend to eat more power, but it doesn’t matter because you’re using them on a simple stereo file, or inserted in a stereo bus, rather than using a lot of instances on individual tracks.

Other goodies. Some people swear by particular plug-ins for mastering, like “exciters,” stereo image wideners, and the like. I tend to avoid these because in most cases, dynamics and EQ cover 99 percent of what’s needed. But in some situations, a little high-frequency exciter helps add a different kind of sparkle than EQ, and once I even added a phasing effect in the middle of a tune during a spoken word part (the client loved it). If a mix has a certain direction, it’s often best to enhance what you have rather than try to turn it into something different.

MASTERING AND ASSEMBLY IN A DAW

You can do album assembly in a multitrack host, either of individual, previously mastered cuts, or of raw mixes that you master and assemble as you go along. With the second option, you bring the tunes into the host program, arrange them in the desired order and, when complete, render the whole thing to disk as one large file. If needed, you can then import this into a CD-burning program to add track markers, CD Text, etc. Note that some programs include CD burning as part of the program.

When assembling within a DAW, files can be placed end-to-end in a single track, each in its own track, or different files in different tracks (Figure 4). For example, one project I mastered had three distinctly different “flavors” of mixes: Some were mixed in a studio that probably had bad acoustics, because the bass was too heavy. Another set of mixes was very neutral (just the kind I like to work with). Another set had compression applied to the master bus, and were already somewhat squashed.

I sorted each type on to its own track, and applied the same processing to like-sounding files — the bass heavy ones needed the same kind of bass EQ, whereas the neutral ones needed a different type of EQ. I also added instances of multiband compression to both of these tracks. The songs that were already compressed didn’t get any multiband compression, but did need a fair amount of EQ. This created a few peaks, so I added a slight amount of limiting.

GETTING CREATIVE

Because you’re assembling in a multitrack environment, you can do tricks that are difficult to do in typical stereo editors. Here are some:

-It’s easy to create just about any type of crossfade within a host, either through an automatic crossfade function where overlapping two tracks creates a crossfade, or by having the tunes on separate tracks and adding fade ins/outs manually.

-For dance or continuous DJ mixes, you can dedicate a separate track for transitions or sound effects.

-Add effects automation to vary effect parameters in real time (e.g., increase a high pass filter’s cutoff as a song fades so it seems to “disappear” just before the next track comes in).

-Use automation to do extremely sophisticated fade ins and fade outs.

This process essentially creates a “meta-mix,” where instead of mixing individual tracks to create a two-track file, you’re mixing two-track files to create a final album.

SETTING LEVELS

Channel headroom isn’t much of an issue in today’s DAWS, which use 32-bit floating point, 48-bit fixed, or even 64-bit resolution. However, when you sum them all together at the master bus, overloading is a definite possibility unless levels are set properly.

Output level clipping indicators aren’t very helpful for serious mastering; an unambiguous numeric readout at the output that indicates the peak level relative to 0 (called the “margin”) is much better. For example, +1.7 would mean the maximum signal was 1.7dB above 0; -0.8 would indicate the maximum signal came within 0.8dB of the maximum available headroom (Figure 5).

Meters that flash these values are helpful, but a “peak hold” feature is more useful because you don’t have to keep watching the meters — just check levels at the end of the song, and adjust the output faders accordingly.

Assuming the faders themselves are also calibrated, here’s an example of how to use this feature. Suppose the current fader setting is 0 and at the end of the song, the readout displays a margin of +2.0dB. Bring the fader down to –2.0, and the next time you play the tune all the way through (after first resetting the meter value, of course), the maximum level should hit 0.0.

However, you don’t want the margin to be 0 but instead slightly less, like -0.1dB below maximum. If a tune has peaks that hit 0 for more than a few milliseconds, it may be rejected by a CD pressing plant on the assumption that those peaks represent distortion.

HOW TO MASTER MASTERING

I certainly don’t mean to imply that following the above techniques will make you a mastering engineer. However, if applied correctly you’ll end up with mixes that sound better than if you’d just left them alone — and that’s the whole point. Besides, if you start working on your mastering chops now, you just may discover a whole new outlet for your creativity.