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Master Class – Perfecting Your Mix

June 25, 2012
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I like to tell my clients that a great mix happens in the last five minutes of work. Because an adjustment on one track can change the way the entire mix sounds, the final tweaks make everything fall into place.
 
Getting there, however, is fraught with danger. Make the lead vocal a couple dB too loud, and the backing tracks will sound wimpy. Allow the guitars too much low-midrange tone to give them warmth and girth, and the mix’s bottom end will sound blurry. Bump up the reverb returns a tad too much, and the wonderful punch you crafted on the kick and bass will go out the window. A few misplaced adjustments are all it takes to disfigure your mix. But conversely, the right nip and tuck will transform it from middling to magnificent.
 
In this article, I’ll offer pointers on deciphering what’s wrong with a disappointing mix and how to correct it. But first, it’s important to mention a common mistake that robs a mix’s potential fresh out of the gate.
 

 
Fig. 1. The center LED ladders for the Brainworx bx_meter show your mix’s dynamic range in decibels. The farther the LEDs extend down from the top of the meters (0dB), the greater your mix’s crest factor.

Avoid Headroom Hara-kiri Starting your mixdown session with all faders close to 0dB is a recipe for distortion and a harsh-sounding mix. On a mix with lots of tracks, start with all faders set considerably lower in order to give your master bus plenty of headroom. You can always raise your master bus fader (or makeup gain for a pre-fader bus compressor) to compensate for any deficit in level, but lowering the master fader won’t undo clipping that occurs at the bus’ input.

If you run out of headroom, you can group all faders for tracks and auxes and pull them down the same amount to prevent clipping the master bus. But because faders usually have logarithmic tapers, linear adjustments across the board won’t fully preserve your carefully wrought balance. Additionally, any pre-fader effects will end up sounding relatively too loud after you lower faders for the tracks that are bussed to those effects. The upshot: Give your master bus more headroom than you think it’ll need.

Watch Your Crest Factor We all know that too much bus compression can make a mix sound harsh and fatiguing. But how do you know when your mix is too hot? While the best guides are your ears, meters that display your mix’s crest factor will also alert you you’ve strayed too close to the sun.

Crest factor is the difference between peak and RMS (or average) levels. The lower your mix’s crest factor, the lower its dynamic range and the harsher your mix will sound. A good rule of thumb is your mix should never have a crest factor lower than 6dB (and that’s pushing it). If your project will be professionally mastered, aim for a crest factor of around 10 to 12dB and let the mastering engineer tweak the dynamic range with his or her superior tools.

Excellent plug-ins that simultaneously show peak and RMS levels include the Waves Dorrough Meter Collection (a bundle) and Brainworx bx_meter. bx_meter also includes a dynamic-range meter that shows your crest factor in decibels (see Figure 1), relieving you from computing the difference between peak and RMS values. Instantiate Dorrough or bx_meter post-fader and after all other plug-ins on your master bus.

If you’re using light or no compression on your master bus and your mix’s crest factor is still too low, your drum tracks might be mixed too quietly or have insufficient attack. Assuming you have enough headroom, try goosing your kick and snare tracks or adding the SPL Transient Designer or Waves TransX plug-in to those tracks to sharpen their strikes (see Figure 2). As always, use your ears to gauge whether you’ve improved your mix or simply made the meters look better!

Hunt Down Distortion Every channel of your mix should have its meters set up to hold clips indefinitely (using infinite-hold mode). After you play through your mix, stop the transport and look to see if clipping occurred in any channel. Check every stage possible for the signal chain (pre- and post-EQ, pre- and post-dynamics and so on) and lower input or output levels wherever clipping occurred to prevent distortion on the next pass through. Just keep in mind that the meters for 32-bit (and higher-resolution) plug-ins may indicate clipping where none has occurred; they show “overs” to warn you that the output of your DAW’s mixer (which might be constrained to 24-bit depth and lower headroom) might clip at its output.

 

 
Fig. 2. The Waves TransX plug-in can be used to increase the attack of trap drums and make your mix sound more dynamic.

For mixes with tons of tracks, the hunt for clipping can entail a lot of work, but it’s worth it. A tiny bit of distortion on each of several tracks can produce an edgy or harsh-sounding mix that no amount of equalization and warming with tube-emulation plug-ins will fix. If you’re pressed for time, at the very least check for clipping on non-percussive tracks such as vocals, string pads and organ; distortion will be most noticeable on sources such as these that produce high RMS levels. You can often get away with some clipping on trap drums; in fact, subtle grit and rounding from mild clipping sometimes sounds great on traps (especially kick and snare).

Check the Width Mixes can sound too narrow if too many tracks are panned close to center, center-panned tracks are too loud, or your mix has too much bottom end. Bass frequencies tend to be highly correlated in left and right channels of stereo tracks; too much bass on a stereo track can therefore cause its image to narrow.

A phase-correlation meter is an excellent tool for checking the width of your mix. The aforementioned Waves Dorrough and Brainworx bx_meter plug-ins each provide excellent phase-correlation metering (see Figure 3). If the meter spends most of its time close to the positive extreme of its range (far-right on a horizontally oriented meter), your mix is probably too narrow and trending toward a mono soundstage. Conversely, if the phase-correlation reading spends more than a brief amount of time to the left of center, your mix is too decorrelated; in that case, it will likely sound washy and it won’t be mono-compatible.

 
Fig. 3. The Waves Dorrough Meter plug-in includes a phase mode useful for gauging the width and mono-compatibility of your mix. Readings consistently far to the right of center indicate a mix that is relatively narrow.
For a mix that’s too narrow, consider hard-panning one or more tracks, especially those with lots of high-frequency content (such as shakers or cymbals). Try thinning out bass frequencies on stereo tracks. See if lowering the bass guitar helps widen the mix without making it sound too bright or thin. Your phase-correlation meter should help you visualize when your mix is spacious enough. As when monitoring crest factor, place your phase-correlation meter post-fader on your master bus and after all other plug-ins.

Use Stereo Imagers Prudently Another way to widen a mix is to use a stereo imager on the mix bus. Injudicious program-width enhancement, however, will lower the level of the kick, snare, bass, and vocals too much and make your mix lose punch. Instead of placing an imager on the mix bus, try widening individual stereo tracks instead. An imager can sound terrific on stereo tracks and auxes that contain a lot of ambience, such as reverb returns and room mics for drums. If your imager is multiband, try narrowing the bass frequencies to mono and widening only the highs; Ozone 5 Advanced includes a stereo imager that works great for this application (see Figure 4). As you work, check the mix bus’ phase-correlation meter to make sure you’re not fattening the cow too much.

Get the Bottom End in Proper Balance The toughest aspect of mixing is getting the bass frequencies in proper balance with mids and highs. If your mix sounds too muddy and the kick and bass guitar can’t be clearly heard, chances are that bass frequencies in other tracks are masking them. Try cutting bass frequencies in guitar and keyboard comp tracks (and any other tracks that don’t need a big bottom) to make room in the low end of your mix for the bass and kick to voice more clearly.

 
Fig. 4. Ozone 5 Advanced’s multiband Stereo Imaging plug-in is an excellent tool for widening your mix’s soundstage. Here, frequencies below 100Hz are narrowed to mono while highs above 10kHz are widened.
If the bass guitar sounds plenty loud but the bottom end of your mix still sounds thin, try lowering the bass track and boosting its bass frequencies. The same strategy often works for kick drum. In most cases, the bass guitar will benefit from heavy compression or limiting to make it ride at a fairly consistent level in the mix.

Of course, you’ll never get the bottom end of your mix in proper perspective if you can’t hear it. Tweaking the bottom two octaves of a mix while listening to monitors with weak bass response makes about as much sense as painting a portrait with sunglasses on. It’s critical to listen to your mix with a subwoofer or full-range monitors—and in an accurate room—to make sure you aren’t adding too much bass to the mix. If your speakers and control room aren’t up to the task, check your mix on headphones that have flat and extended bass response.

It’s equally important to make sure the bass and kick don’t disappear when listening back on midrangey speakers. Band-limited consumer proxies such as Yamaha NS-10M Studio and Avant Electronics Avantone MixCubes are great monitors for this purpose. Alternatively, see how the bass instruments sound on a home or car stereo, computer speakers, or a boom box. If you can’t hear the kick and bass on these speakers, they’re probably mixed too low. If kick drum hits clip the speakers on your boom box (set to flat EQ), the kick probably has too much bottom end.

Solo the Side Channel If you find yourself struggling to get enough bottom end on your mix and boosting the bass frequencies on your kick drum track isn’t helping, your kick drum might be out-of-phase. This is sometimes a problem when poor stereo kick drum samples are used in a production. The way to tell if this is the case is by soloing the side channel, using a plug-in such as the Brainworx bx_meter or bx_control V2 that provides mid/side monitoring. If you hear the kick drum’s dry sound while soloing the side channel, your kick drum is out-of-phase and no amount of bass-EQ boost will give you the bottom end your mix needs. Adjust the phase on one channel of the kick sample or replace the sample with one that’s in-phase.

Check Levels for Vocals and Guitar Solos To place the lead vocal in proper perspective, check your mix on midrange-y monitors that have weak bass response. (Listening to monitors with ample bass response makes the tests I’m about to describe more difficult; you want to use speakers that provide an isolated window into the midrange band, where vocals and guitars mostly reside.) While listening to your mix, confirm that the background vocals aren’t louder than the lead vocal. Also make sure overlapping guitar fills don’t obscure any lyrics; ride the guitar’s fader down in spots where it would otherwise mask the money track. Generally speaking, a guitar solo should not be louder than the lead vocal; if it is, the vocal will sound under-powered when it reenters after the solo.

While the lead vocal is singing, turn your midrange-y monitors down to the point where they’re barely audible. If the lead vocal disappears before the instrumental tracks do, it’s mixed too low. Be sure to also check how the lead vocal sounds on full-bandwidth monitors. Many two-way monitors have crossovers that recede midrange elements such as vocals slightly into the background. Make sure the lead vocal can still be clearly heard on such monitors and on all other systems you have access to.

Keep Notes A great mix might require a few hundred or more dynamic adjustments to fader levels, EQ, panning, and effects parameters. Keeping mental track of the net effect of each of these moves is a daunting task, and it’s easy to miss the forest for the trees. When you think your mix is finally in great shape, listen back on all the monitors at your disposal and take notes of any problems you hear. Make a checklist of changes you’d like to make in a remix to fix those problems: “Boost the bass guitar’s EQ around 1dB at 200Hz” (if it sounds too thin on midrange-y speakers), “dip the lead guitar solo on the last note coming back into the final chorus” (if it obscures the vocals), and so on. Then mix the song again, incorporating the ideas in your checklist.

Listening back to the mix that you’ve tweaked, you’re likely to hear additional problems you didn’t previously notice or that were introduced by the new mix moves. Make a new checklist and mix again. Repeat the process until you have no more complaints. Your mix is now killer.

Michael Cooper is a mix and mastering engineer and a contributing editor for Mix magazine. You can hear some of his mixes at myspace.com/michaelcooperrecording.

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