By Michael Cooper.
As a mastering engineer, I hear a lot of mixes from other studios. Some are great, some are not. But what is striking to me is that the mixes that need help usually suffer from many of the same problems. The good news is that these shortcomings can all be avoided or corrected by using a few simple techniques.
In this article, I will describe 12 common problems with wayward mixes and discuss how to solve them. If your mixes are routinely restrained by a lack of punch, clarity, and detail; if your productions are held hostage by unruly dynamics and spectral imbalances; or if your results don’t sound as wide and deep as the mondo tracks created by your competition, read on for some liberating pointers. I’ll address each problem and its solution individually, beginning at rock bottom.
Boomy or Thin-Sounding Mix
The most common problem I hear with mixes is uneven levels throughout the range of bass frequencies. This can present itself as either a thin-sounding mix or a boomy one. Some mixes sound alternately thin and boomy in different sections of the song.
The main culprit behind a skewed bottom end is mixing in a room that has not been properly treated with acoustic products to help tighten up impulse response and attenuate room modes. (Room modes, aka standing waves, are narrow peaks and dips in frequency response; they are especially problematic in the bass range.) These acoustic problems might lead you to, for example, unnecessarily boost certain bass frequencies to compensate for a thin-sounding mix when, in fact, the mix already has a perfectly balanced bottom end, though the room’s uneven bass response at the mix position is telling you otherwise.
In truth, even rooms that have had thousands of dollars poured into their acoustic makeovers usually have some persistent problems with uneven bass response (although the inaccuracies are usually dramatically reduced in number and severity with proper treatment). Typically, one or two prominent room modes remain at the mix position, making it difficult to properly assess the mix’s bass content in these narrow bands.
In most control rooms, there is at least one spot where specific room modes and other bass-response anomalies that compromise monitoring at the mix position are much weaker or even completely tame. While this alternate bass-reference spot might have other problems and be less accurate overall compared with the mix position, it gives you another reference for bass balance in the narrow bands you can’t hear properly at the mix position.
How can you tell where the alternate bass-reference spot is? First, assuming that you have more than one pair of reference monitors, play a respected, full-bandwidth mix (usually one that a prominent record label has had mastered and released) through the speakers that have the deepest bass response (include a subwoofer if you use one). Choose this reference mix carefully: it should be one that has always sounded great on the bottom end no matter what sound system you’ve played it on.
Walk around your control room while the reference mix plays, listening to how the sound of the bottom end changes as different acoustic influences come in and out of play. Note the spot where the bass response sounds the most even at the specific bass frequencies that are out of whack (too weak or too strong) at your mix position — that spot should become a second place you go to check the bottom end when making bass-EQ decisions on your mixes.
Unfortunately, the alternate bass-reference spot is often inconveniently located with respect to the studio’s mixer or DAW controller. For example, the place where the 40 to 45 Hz band is most accurate in my control room is about 3.5 feet in front of the back wall.
There is an easy solution: remote control. I always use my Frontier Design Group TranzPort wireless DAW controller when checking a mix’s extreme bottom end at the back of my control room. Using the TranzPort to remotely start and stop playback allows me to set my control room’s monitoring level high enough that I can really hear those subterranean frequencies without blasting my ears at close range. I listen, evaluate the bottom end, stop playback, make the relevant EQ adjustments at my mixer, and repeat the process until the bass sounds great at both the mix position and the alternate bass-reference spot.
Edgy, Fatiguing Sound
Digital audio has a reputation for producing cold, brittle sound, but the problem often stems from poor engineering techniques. The most common factor contributing to an edgy, fatiguing mix is indiscriminate boosting of upper-midrange and high-frequency EQ on multiple tracks.
Here’s a typical scenario: hours of mixing at high sound-pressure levels (SPLs) progressively compresses your ears’ high-frequency sensitivity, and they become starved for the highs they’re missing. To compensate, you boost the highs and upper mids to get back the detail and presence your tired ears can no longer hear clearly.
You check your mix the next morning after your hearing has recovered, and it’s like fingernails on a blackboard. Rather than cut the offending frequencies, you opt to boost the bottom end to warm up the mix. Now you have phase shift (unless you’ve been consistently boosting using a linear-phase equalizer) and alternating peaks in response across virtually the entire spectrum, resulting in an overly edgy sound, not to mention decreased headroom.
The solution is to mix at lower SPLs and to cut offending frequencies whenever possible instead of boosting other frequencies to compensate. For instance, it usually sounds better to carve away bass frequencies than to hype the midrange EQ when trying to make a mix sound more present. As a general rule, using EQ to cut will sound better than using it to boost.
Other factors leading to a harsh-sounding mix include having too many midrange instruments in the arrangement or mixing them too up front with respect to the other elements. Know when to lower that bright organ pad to mellow things out a bit. Similarly, do you really need those 13 electric guitar overdubs? Consider muting some of the midrange elements that aren’t essential and that only make the mix more fatiguing to listen to. Often the problem with a mix lies with the arrangement, and no amount of EQ will help.
No Sparkle and Bottom
Of course, sometimes EQ boost is needed to make a mix sound great. You can generally get away with boosting extreme bass and high frequencies more than you can boosting midrange frequencies. That’s because the human ear is less sensitive to phase shift at the extremes of the audible spectrum. Even after boosting the bass and highs a bit, you may find that your mix still doesn’t have the huge bottom end and sparkly highs you yearn to hear.
Again, the reason may be that you’re listening at too loud a level while making EQ decisions. That’s a problem because the human ear is subject to the Fletcher-Munson effect. In plain English, this means the ear is much less sensitive to bass and high frequencies when listening at low volumes than at high volumes. (Many consumer stereos have a Bass Loudness button to compensate for this reduced sensitivity to bass frequencies at low listening levels.) Ear fatigue aside, if you adjust EQ to taste while monitoring at loud levels, your mix might not sound sparkly and thunderous enough once the playback level is turned down.
Knowing this (and to preserve my hearing), I spend most of my mixdown time with my monitors set no louder than a spirited two-way conversation, and I’ll often set them a lot lower. If I can get the mix to scintillate and thunder while listening at that low level, it is going to absolutely rock when it’s cranked. Also working in my favor, my high-frequency sensitivity won’t be trashed by sustained listening at loud levels, helping me retain an accurate perspective of spectral balance. That said, I will crank my control room monitors for about 20 seconds or so every hour when I’m mixing to confirm that the bottom and top ends still sound great and that I haven’t taken any EQ boost too far.
One other point: if you compress tracks such as bass-guitar and cymbals post-EQ, the compression will at least partially negate the effects of any EQ boost on those tracks. Try placing the compressors before any EQ boost to get more sparkle and boom.
Large Swings in Spectral Balance
Sometimes the timbre of specific elements of a mix (or of the whole enchilada) is a moving target. For example, the electric bass or acoustic guitar might sound boomy on some phrases yet be well balanced everywhere else in the song. The lead singer might have a shrill high register that bites your head off during the choruses, whereas the lower register sounds perfect during the verses. Or the entire mix might get edgy when, for instance, a bunch of midrange instruments pile on for one section of the song.
In these cases, static EQ settings won’t sound good throughout the song. One worthy solution, albeit a time-consuming one, is to ride the EQ on individual tracks as needed. But a quicker and sometimes more elegant-sounding fix is to slap a split-band (aka multiband) compressor on the unruly tracks — or even on the entire mix. A split-band compressor divides the audio spectrum into multiple, adjustable frequency bands so that each can be compressed independently. Examples of outstanding split-band compressors include the Tube Tech SMC-2BM (a high-end analog unit) and the Waves C4 Multiband Parametric Processor, Waves Linear Phase Multiband, and PSP VintageWarmer 2 plug-ins.
Adjust the bandwidth of one or more of the split-band compressor’s bands to include only the frequencies that exhibit large swings in level (for instance, bass frequencies that sometimes get too loud and make the mix boomy), and bypass the other bands. Then set each active band’s threshold to be at or slightly below the level where the offending frequencies begin to annoy. Adjust each active band’s ratio, attack, and release controls to taste to limit how much (if at all) the unruly frequencies can bloom above the thresholds you’ve set. With the proper settings, a split-band compressor will automatically nip large swings in spectral balance in the bud. (For more in-depth information on how to use split-band compressors, see “Let’s Split!” in the January 2004 issue of EM, available online at www.emusician.com.)
Insufficient Detail
When a mix is lacking in detail, boosting high-frequency EQ is often the wrong approach. When that just creates a glassy mix without solving the problem, try cutting the upper-bass and low-midrange frequencies instead. Too much energy in these bands can create a blanket of mud that obscures a mix’s underlying transients, so try cutting between 200 and 500 Hz before boosting highs. Just be sure not to overdo it, or else you’ll end up with a thin mix and too much detail.
Another thing to consider on a cloudy-sounding mix is whether sustained sounds such as string or synth pads are too loud. By simply lowering some or all of the tracks that exhibit minimal transients and loud average levels (sustain), percussive elements will more readily punch through. The end result will be a mix with plenty of detail that nevertheless retains its warmth because of minimal use of EQ.
A mix lacking detail will also often lack punch, or transient elements married to tightly focused bass-frequency content. When a mix’s spectral balance is already great, it can be a mistake to boost both bass and high frequencies to achieve more punch. The added highs might just make the mix sound glassy, whereas the extra bass boost could make it boomy.
Instead, use a dynamics processor to emphasize the attack portion of the low-frequency elements from which you want more punch (for example, trap drums and electric bass guitar). A solid-state, VCA-based compressor set to relatively slow attack and fast release times (start with 60 ms for each) will often do the trick.
Too Much Compression
These days, many mixes are so overcompressed that they become irritating and fatiguing to listen to after only one or two minutes. Overcompression is like a plague contaminating our industry. Make no mistake — I love stereo-bus compression, and I like my mixes loud, but there’s a big difference between pumped-up, exciting dynamics and just plain annoying noise and distortion.
The old saw about using your ears when determining how far to push mix-bus compression is all well and good, but I have a more practical suggestion: watch the crest factor on your stereo-bus meters. The crest factor is essentially the difference between peak and average levels, and keeping tabs on it is a good reality check against what ears addicted to volume might otherwise be pushing to accomplish.
Spend time listening to your favorite records — particularly those that have dynamics you’d like to emulate in your mixes — patched through the 2-track return of your mixing console or DAW, and keep a close eye on the meters. (Make sure that the meters are peak reading and set to prefader listen, and that all processing is disabled.) Note how much the meters rise above average levels during transient peaks throughout various sections of each song. Then shoot for roughly the same crest factor in your mixes. You can learn a lot by being a good meter reader.
The Chorus Doesn’t Climax
You had high hopes for your new power-pop ballad, but something is holding it back. Your tracks were all captured with plenty of dynamic range, the performances were killer, and the arrangement positively soars during the hook. Yet for some reason, the chorus just doesn’t deliver the big payoff it should in your mix. It’s time to look at your mix-bus compressor settings again.
Sometimes an engineer will set up the mix-bus compressor for a big, in-your-face sound at the beginning of mixdown, when working on relatively quiet verses, and will just assume it’s going to sound even bigger during the choruses and other climaxes. A compressor with too low of a threshold and too high of a ratio will suck the life out of the hook when it hits — sometimes the chorus will actually sound lower than the verses. Raise the compressor’s threshold and lower its ratio to no more than 2:1 to give the hooks room to explode. You might also need to back off the compressor’s attack time a bit.
Washy Sound with No Depth
Adding reverb to a mix is a great way to make it sound bigger. The larger the implied acoustic space, the more depth and width the production takes on. But running virtually everything through reverb in an attempt to make the mix sound huge is a common mistake of neophyte mix engineers.
Something can sound big only if something else sounds small. In part, it’s the contrast between close-up and far away that gives a mix depth. (The nuance captured by superior mics and mic preamps is another contributing factor, but that’s a discussion best left for another article.)
When many tracks are drowning in reverb, everything begins to sound indeterminately far away, and there is not enough of an anchor for the brain to get a picture of what is psychoacoustically up-close. Not only has depth gone out the window at that point, but the mix also takes on a washy character dominated by diffuse echoes that blanket any semblance of detail and punch.
One solution, of course, is to make some tracks very dry. You might even need to make a lot of tracks completely dry in order to attain the depth you desire. Instruments that produce inherently sustained or reverberant sounds, like cymbals and strummed acoustic guitars, often benefit by turning their reverb sends way down or completely off. That’s especially true of dense arrangements that are prone to drown in ambient soup. The acoustic guitar already supplies built-in reverb from the resonating chamber that is its body. Piling on a bunch of additional reverb makes little sense, unless that instrument is being played in short, percussive bursts such as during a largely monophonic introduction or solo.
Despite the foregoing, there are instances where a healthy dose of time-based effects is needed to create the desired sonic landscape. In such cases, try adding predelay to some of your reverbs, or try substituting single echoes or multitap delays for reverb effects. These alternatives allow the dry signal to voice before the effect kicks in, giving a front-to-back effect in the soundstage that can really enhance perceived depth while preserving detail.
Another remedy for a washy mix is to eliminate one of the channels of a stereo track, thereby reducing that track to mono. Converting most of your stereo tracks to mono will help provide the pinpoint imaging that is a remedy for a washy mix. Conversely, using a lot of tracks that were recorded with spaced-pair stereo-miking is a recipe for mud soup. Each of those tracks is a rendering of an instrument playing in an acoustic space, and simply panning them differently to separate them won’t necessarily lend focus and depth to your mix.
Panning a few stereo tracks across the stereo field is a common strategy. But if you pan one stereo track hard left and at ten o’clock (for left and right channels, respectively), another at ten and two o’clock, and a third at two o’clock and hard right, what have you accomplished? You now have three small rooms in a left-center-right arrangement superimposed over whatever other acoustic spaces are implied by added reverb on other tracks. No wonder the mix sounds washy!
In summary, to clean up a washy mix: Keep a number of your tracks mostly or completely dry. Mute one side of one or more stereo tracks. And use discrete delays and reverb predelays to create depth without sacrificing detail.
Collapsed Stereo Image
Suppose you’ve hard-panned a number of tracks, but your mix still doesn’t sound as wide as you’d like. What’s wrong with this psychoacoustic picture?
Your hard-panned tracks might have too much bottom end. Bass frequencies are inherently omnidirectional, meaning it’s hard for the human ear to determine where they originate. That’s because bass frequencies have long wavelengths, and easily wrap around the listener’s head to either ear with minimal phase difference.
From a stereo-field perspective, tracks that are panned hard left and hard right are potentially the most directional elements of a mix, whereas center-panned tracks are the least directional. The more the prominent omnidirectional bass frequencies are in hard-panned tracks, the more the hard-panned tracks’ perceived positions in the stereo field get pulled toward the center. Conversely, rolling off bass frequencies on hard-panned tracks will move them farther from the center.
There is no magic frequency at which omnidirectionality occurs. Sound becomes progressively more omnidirectional as its frequency gets lower. So the lower in frequency the bass content of a panned track, the more it will move toward the center (assuming that the high frequencies also present in the track don’t compensate). Even hard-panned tracks with a lot of low-midrange frequency content will move slightly toward the center image.
To make a mix sound wider, try rolling off the bass and possibly some low-midrange frequencies on hard-panned tracks. Also, hard-pan tracks with lots of high-frequency content — such as cymbals, shaker, and piccolos — to gain more apparent width. If you still need more width in your production, running a single stereo track through a stereo-imaging plug-in such as Waves S1 Stereo Shuffler or iZotope Multiband Stereo Imaging (which is part of the Ozone 3 multicomponent plug-in bundle) will do the trick nicely. Be judicious, however; using this kind of processing on multiple tracks or on an entire mix can quickly make your production swim in a washy, diffuse soup.
Setting the perfect vocal level can be difficult. The vocal’s balance with respect to other tracks will always sound different on different monitors. What works for me is listening on bass-challenged monitors such as the Avant Electronics Avantone MixCubes or the discontinued Yamaha NS-10M Studio. Without prominent bass frequencies masking the lead vocal, I can more accurately gauge how loud the money track is with respect to the other tracks.
If you have only one set of reference monitors and use a subwoofer, turn off the subwoofer when setting the level of the lead vocal. Also, listen to the mix at very low volume to let the Fletcher-Munson effect decrease your perception of bass and high frequencies. That will leave you with an unobstructed window into the midrange, where the lead vocal primarily sits.
Slowly turning down your close-field monitors to the point of almost dead silence is another effective technique. If the lead vocal is the last track to become inaudible, you’ll know it’s loud enough to be easily heard on most if not all systems. If it’s still relatively loud when all the instruments are practically mute, the lead vocal probably needs to be turned down.
Of course, some styles of music call for louder vocals than others. For example, the vocal should generally be mixed louder on a country song than on a rock production. But these guidelines should give you the needed perspective to make the right judgment call for your chosen format.
Vocals Alternately Dip and Stick Out
Lead vocals typically benefit from compression. That helps them sit at the proper level throughout a mix. Compression limits the dynamic range of the track so that it becomes neither too low nor too loud in the mix on any given phrase. But with a very dynamic vocal, it may be impossible to compress aggressively enough to accomplish this goal without completely squashing the track, ruining its timbre, and destroying any depth and nuance. If, after you push the compression as far as you dare, the vocal still dips too much on some phrases and sticks out too much on others, here are some alternatives.
Try chaining two or more compressors together in series, with each adjusted to more moderate control settings so that no single one is going to squash the track For instance, the first compressor could have fast attack and release times and a high threshold setting so that it kicks in with its high compression ratio only during peaks. The second compressor might be set to a relatively low threshold and ratio and moderate attack and release times so that it is processing average levels pretty much all the time, but with kid gloves. Here, the second compressor isn’t expected to clamp down on transient peaks, so it can be set for more moderate action on average levels that will preserve the track’s timbre and nuance. Meanwhile, the first compressor needn’t have its threshold set so low that it will rein in the average levels of the vocal track — that’s the second compressor’s job, and it will do it more gently.
Despite the time-tested procedure of chaining compressors together in series, Roger Nichols Digital offers a far more powerful and elegant solution to reining in extremely dynamic vocals. The company’s groundbreaking Dynam-izer plug-in divides a track’s unprocessed dynamic range into as many as four mutually exclusive and contiguous zones. It can then independently compress or upwardly expand the track across each zone using different ratio, attack, and release settings. The key point here is that each compressor or expander applies processing only across the input-level range to which it is assigned. You can, for example, optimize the zone settings to upwardly expand the quietest vocal phrases, gently compress moderately loud sections, and smash transient peaks forcefully.
After using the foregoing techniques, the lead vocal still might fluctuate too much in level on a few remaining phrases. Don’t be afraid to ride the track’s fader to even out those sections of the vocal, and record your fader moves with your DAW or mixer’s automation. Also, some buried lyrics may be brought out more effectively by boosting upper-midrange or high frequencies rather than riding the fader (remember to undo the EQ boost immediately afterward). In some of my mixes, the lead vocal’s track will have dozens of fader and EQ moves over the course of a three-minute song, depending on how even the singer’s performance was. Don’t be afraid to do whatever is necessary to make the vocal track perfect.
The Perfect Mix
None of the techniques discussed in this article will lead you to a great mix on their own. They must all be taken into consideration at once and balanced against one another. For instance, striving for too much detail and clarity can result in a thin, icy mix that will sound even more fatiguing if brickwall limiting is applied to achieve competitive loudness. And a mix with too wide of a stereo image and key tracks panned hard left and right might lose needed center focus and punch.
Keep your original vision for the song in mind while you mix, asking yourself along the way if any of these 12 problems are beginning to creep in. Note if any corrective tweaks you perform introduce their own problems, but be aware that effective mixing usually entails a series of smart trade-offs. Putting these compromises into perfect balance is the key to an outstanding mix.
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