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Thursday, April 7, 2011

Mixing 101

There they are...8/16/24/48/96 tracks that you’ve painstakingly recorded, overdubbed, erased, and recorded some more.... so now what? You can’t play with your mixer’s knobs every time you want to hear your masterpiece! You need to blend all those tracks to (usually) a 2-channel, stereo mix. In other words, mixdown your tracks.    
Great --- so what does THAT mean? Well... first - you need something to mixdown onto - a computer, a stand-alone hard disk recorder (such as the ubiquitous Alesis Masterlink), a 2-channel reel-to-reel, a HiFi VHS machine, a MiniDisc recorder, or even a cassette deck -- all are usable options (some more usable than others!) The pros and cons of each format are beyond the scope of this article, but suffice it to say, use the highest quality recorder your budget will allow.
I'm also going to have to presume you already have a decent monitoring chain in place. You can't make good sonic decisions if you can't properly hear what your tracks sound like! And it IS true - headphones are not considered a "decent monitoring chain." While they are useful for double-checking your mix, and proofing it for noise or artifacts that don't show up on the monitors - they are horribly ineffective as a primary mixing tool.
You also want to pay attention to the volume of your monitors as you mix. There are many different preference engineers take to levels, but it is commonly accepted that 85dB SPL is where human hearing frequency response is most flat, and this is typically where many engineers leave their levels at... it is good practice though, to vary listening levels while mixing to get a feel for the mix balance at different volumes. Mixing too loud almost always results in unbalanced mixes, mixing at softer levels usually produce more balanced results.
   
Next?
Mental preparation......... rest your ears, rest yourself... it’s virtually impossible to mix right after a tracking session, or after going to a concert.... you need your ears to be in top form for analyzing and objective & critical listening... what works for me is starting fresh in the morning, when my ears are most rested....
OK - I’m rested, my ears are rested -- let’s do this thing...........
Well.... throw up the faders and see what you have to work with.... yes, ALL of them.... what you want to listen for are the tracks that are working, and the tracks that aren’t. Yeah, the guitars are fighting during the choruses, the background vocals aren’t working midway through the verses, the lead solo starts too early.... and of course, you’re taking notes for yourself as you do this...
The plan here is to take out the stuff that’s not working together, and leave in the stuff that IS working.... there are a couple of ways to do this: 1) use EQ to tailor the portion of sonic spectrum a track will fit in, and 2) mute the track at the problem spots.
   
Let’s talk about muting....that’s right, you pull the track right out of there! If it doesn’t help the song it doesn’t belong - period. Mixdown is the time to be blatantly critical of every track that’s been put down... you don’t reduce the volume, you don’t bury it behind something else - this simply results in messy mixes -- it either works, or it doesn’t......... you will accomplish muting either by automation (via software or mixer hardware), or the old-fashioned follow-the-timelog-with-your-hands-on-the-mute-button technique. You don’t have to mute the track completely either - you can add interest by pulling it in and out of the mix at key spots (obviously not at the places where it’s causing mix difficulties!)
"But I like the track that doesn’t work!"
Let’s be honest... sometimes the track works, but is simply frequency-fighting with another track.... in this case, you probably don’t want to mute the track, but you need to shape it so that it doesn’t interfere with another track’s piece of the sonic pie. So....... what you reach for are the EQ knobs....
   
First, some EQ background.... it’s not cut-and-dry -- there are various ways to use EQ, and EQ decisions you may have made during tracking will affect the mix process.
The addition of EQ into the signal chain always results in "some" compromise of the waveform by introducing phase-shifts (time-based artifacts that can results in comb-filtering of the waveform) - especially when boosting frequencies. Cutting frequencies can result in less of these artifacts, so it is generally advisable to apply EQ by cutting frequencies you don't want, rather than boosting the ones you want to enhance - a practice known as subtractive EQ. The quality of the EQ itself also dictates the artifacts - cheap EQ gear means more artifacts, mastering-grade EQ means significantly less (for comparison, a Weiss EQ-1 used by mastering houses runs about $5500 US)...
So, using EQ to shape sound is a bit of a compromise - yes, it changes the signal, but it introduces "some" small signal degradation.... the obvious solution is don't use it--- er, at least, not until absolutely necessary. "But wait...", you say, "I need it, my guitar/bass/drums don't have that sound..."
Well ok... for line-level instruments such as synths, you certainly can use EQ to shape the sound.... but for mic'd sources, it's much better to use mic selection and mic placement to get the sound you're after, rather than reaching for the EQ knobs.... for example, don't brighten an amp by boosting your hi-shelf EQ - change amp settings, change guitar pickups, change amps, move that mic closer to the center of the cone... if you're not getting the sound you want, maybe you're using the wrong instrument/amp combination!
Another point to keep in mind - try to get your tracks sounding the way you want during tracking - if the tracks "to tape" are sounding the way you want them, then selecting sounds during overdubs become much easier. And even better, during the mixing phase, you'll find your tracks will blend better (since you've already blended them correctly in the tracking process!) Best guideline to follow: never "fix it in the mix" - fix it now - move a mic, change the mic, change the source, move the source, switch rooms. If none of these work, then reach for EQ!
During mixing - if you've done your tracking homework, there should be less work needed in getting the tracks to fit, since you've taken so much care during the tracking process. But very likely, there are still some tweaks you'd want to make.... I strongly suggest you adopt the subtractive EQ approach - cut instead of boost. If there are too few highs, remove some mids or bass to shape it. This does two things - minimizes phase-related artifacts, and more importantly, reduces unnecessary signal level that will eat into your mixer's headroom (since cutting will reduce the amount of frequency "space" a waveform will take up.)
   
Well - that’s the basic EQ theory... so now we’re going to shape the tracks of our mix with EQ. To do this you do have to have some concept of the audio picture you’re about to paint, within two frames of reference 1) the various frequencies of the tracks, and where they sit; and 2) the placement of the tracks in the soundstage in front of you (between the left and right speakers).
The charts below will give you some indication of the frequency ranges for various sound sources that will help guide your use of EQ.

1/3 Octave Frequency Charts **
Audio Octave Ranges


These charts, however, don't tell you the whole story.... the two frames of references I mentioned earlier are related in terms of their effect on the sonic soundscape of a mix.
Think of a mix as a 3-dimensional space in front of you... you have control over the left/right, the high/low, and the front/back of the sound stage. The tools that let you manipulate this area are Panning (for left/right positioning), EQ (for high/low positioning), and Fader Level (for front/back positioning).
Homing in on EQ for the moment, keep in mind that as you shape your tracks, higher-frequency tracks will appear to come from higher up in the monitors than lower-frequency material. This can be useful in positioning guitar tracks - if a guitar track is fighting with something else in the mix, you can "move it away" from the offending track by removing some bass content in conjunction with panning.
As for Panning - it alone can also be used to separate mix elements into distinct positions in the mix. For example, panning a keyboard rhythm part off to one side while panning a complimentary rhythm guitar part to the other will result in a pleasant, wide and full rhythm section whose elements don't interfere with each other. When using panning, it is often helpful to envision a music stage in front of you, and place the tracks within that space as you would normally hear at a concert. You may not keep the tracks in this position as you build-up and further define your mix, but it does make a useful starting point.
And finally, Level -- faders allow you to control the level (and thus how close or how far away the source is) of the track in the mix. No tricks here except that you really shouldn't use level to hide a track -- if the track doesn't work, simply mute it..... you want a track to be more "in your face" move it closer to you, you want it to sound as if it's further away (like towards the back of the stage!), lower the level.
An extremely important point to remember is to maintain your relative levels so that you don't eat away at your mixer's headroom -- if you've set all the levels of the tracks and find you have to push your solo track level very high for it to cut through, then you've got all your other track's faders set far too high. Unless you've got 6-digit consoles that are more forgiving of "level-pushing", most mixers will start sounding pretty harsh if pushed too hard.
   
But wait a minute! What about reverbs, delays, and all those cool other effects -- you didn't mention a thing???
Well yes... effects play an important role in mixing - much like spices do in fine cuisine. It's all in the way you use them... and the topic merits its own full-blown article (maybe in the future), but for the moment, here's a brief overview.
My own approach is that unless a particular effect is an integral part of a track's sound (such as a chorus, or wah on a guitar part), I leave all effects until the mix stage. The tracks really should stand on their own merit without any effects added-in, then you make the mix bigger, fatter, wider, with careful and judicious use of things like reverb, delay, choruses, etc.... little touches such as timing delay and chorus settings to the tempo of a track really do a lot to make the tracks shine. Overuse of effects results in muddy, poorly-defined mixes, so much like EQ - less is usually more. As well, pay particular attention to reverb used for vocals... for most listeners, vocals are the component of the song that reach the people first, and poor effects, or bad EQ is immediately noticeable -- it's not uncommon spending hours on reverb selection for the lead vocal track!
One effect that is very misunderstood (and often poorly used) is compression -- this effect can be an important part of a polished sound both during the tracking AND mixing stages of the production process, again, if used properly. A colleague of mine wrote an excellent article (with examples) on the use of compression... check out Moshe Wohl's Description of Compressing/Limiting for some great notes on the subject.
   
So we've tamed our tracks with EQ, balanced fader levels, set up some nice ambient effects, you've made your muting/adjustment notes and everything is sounding great... this is the "work" part of the mix -- the previous tweaking was the "fun" stuff, now - depending on how many mutes, volume, pan and EQ adjustments you have to make (if you have mix automation, it's a no-brainer!), you'll want to rehearse your mix a few times before hitting Record on the mixdown unit.
In this process you treat the mixing console like an instrument - following your notes as you go along. At 01:10:25 drop level to -5db on track 3, 01:40:30 mute track 6, you get the idea... The point is to become familiar enough with the mix moves you have to make so that you're not looking at your notes so much that you miss something. For complex mixes, get your bandmates/family/girlfriend to help you with an extra pair of hands! Once you've got the mix moves down smoothly, fire up the mixdown recorder!
A quick note on mix levels -- it's a very good idea to keep your levels strong and balanced throughout the mixing process. Having to turn up the recording level on the mixdown unit because you've got the levels too low on your mixer usually results in unnecessary noise and possibly distortion if the levels are extremely diverse. Remember that all gear has an optimal signal level range and your best results are obtained by staying within it. Know your gear and what's it's capable of handling in terms of low-level noise and high-level distortion. In addition, use the meters as a guide, but always let your ears make the final decision -- you hear with your ears, not your eyes!
   
So.......... once you've got that mix take down and you like the way it sounds, you're done, right??? Wrong...... you've only just started! You can, of course, stop there - but you very likely won't be pleased with the result.... you've spent all that time and energy getting balances and levels right, only to find that when you play it in the kitchen boombox, it sounds very different. The fact is - you do have to learn how to translate your mixes from your monitoring system to other systems, and as well, learn what works for a mix everywhere, and what doesn't.... and there's no way to describe it - you have to learn by experience. What this means is you will follow this approach of performing a mix, checking the sound on various sound systems, coming back and readjusting/rebalancing some mix elements, performing another mix, etc... for a few iterations until you've honed it to a point where the mix sounds reasonably good on most systems.
Take heart though - as you learn mix translation with your system, it does become easier - and with enough practice, you'll develop a feeling for what works and what doesn't.
   
The art of mixing is very broad...
There are various mixing guidelines for all the many styles of music (you don't mix a big band song the way you would a pop song); and within each mix style there are commonly accepted practices. What I've tried to describe in this article was to provide an overview of some basic mixing practices that are common to all mixing styles, as well as some functional tips regarding one of the most abused mixing practices - EQ.
The best way to approach mixing is to read as much as you can about common approaches, while at the same time, practicing the techniques you've read about and adapting them to suit your own needs. 

Some recommended reading related to the art of mixing are:
  • Modern Recording Techniques - Huber & Runstein  
  • Mastering Audio - The Art and the Science - Bob Katz   
  • Behind The Glass - Howard Massey  
    Behind The Glass Vol. 2 - Howard Massey   
  • The Mixing Engineer's Handbook - Bobby Owsinski   
  • The Recording Engineer's Handbook - Bobby Owsinski   
  • The Art of Digital Audio - John Watkinson   

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