Audio Mixing
Back to Basics: Four steps to tighter mixes - from the mastering perspective.
(also published in EQ Magazine)
his section was published in the October 2000 issue of EQ magazine. It covers four areas that experienced recording engineers
take care of automatically: how to create problem-free mixes that are ready for
mastering. Let's assume that you are working on a Rock track with electric
bass, drums, guitars, keys and vocals. You need a stereo mix for radio release.
The Stereo Field
The stereo field is a both a way of determining how instruments are positioned
from left to right, and a way of creating a sense of depth behind the speakers.
The two common tools for creating it are the panpot, which positions a sound by
controlling it's volume in each channel, and reverb, which creates sense of
space. The short delays at the beginning of a reverb signal, called early
reflections, create "room sound" and a feeling of size, while the longer
reverb tail can simulate a large space and add depth.
- Panning tips: Keep instruments that convey power and solidity in the center,
unless you want a retro ping-pong stereo feel. Kick, snare, bass, lead vocal
and most instrumental solos all can benefit by staying in the center. Doubled
crunch guitar tracks or keyboard parts, plus background vocals, can often be
panned way out to create a sense of space. The Fender Rhodes piano is also a
natural for this treatment. Toms and drum overheads can be placed at least
halfway out with good effect.
- Monaural compatibility: One hallmark of pro mixes is that they sound great in
mono. This is important for songs that will be played on FM radio. In fringe
listening areas, most stereo receivers automatically revert to monaural
reproduction to reduce noise. You can't control when this will happen, but you
can make sure that you don't aggravate the problem. Frequently hit the MONO
button on your console when you record and mix. This combines the left and
right channels into one signal that is sent to both speakers. When you switch
to mono, the image will collapse to the center, but both the tones of the
instruments and their relative volumes should stay the same. If the sound of an
instrument changes drastically, the likely suspect is time delay.
- Digital delay lines, guitar processors, synths and stereo room mics can
generate wide stereo output. Check all of these channel pairs closely for mono
compatibility. Short time delays can produce huge stereo effects, but when the
two channels recombine, all out-of-phase information will disappear, along with
the sense of size that it created. In extreme cases, an instrument can change
tone completely or vanish from the mix in mono!
- (Note: If you have a stereo instrument track that sums poorly to mono, try adding a few milliseconds of delay to one of the channels. You may be able to "time-slip" the track back into mono compatibility. This is easy if you have a digital editor such as ProTools or SAW. Just drag and drop one side of the pair. This may save you having to re-track the part!)
Mix Balance
After the instruments are positioned, you need the right volume and correct
tone for each one. Volume is fairly easy to set. We've all heard well-balanced
mixes on CD and radio. If you can clearly hear what an instrument is playing,
then the volume setting is close.
The tone part is harder. For discussion, tone can be broken down into two
components, spectral content - bass, mids, highs - and attack, the leading
edge of a note. On a wide-range instrument, the fundamental tone conveys
power, the lower harmonics (midrange) convey sense of fullness or presence,
and the higher harmonics, attack and definition. A few examples:
- Midrange Guitar and keyboard leads need to be forward in the mix. To make
this happen, many people reach for the midrange EQ control. The 1 kHz to 2 kHz
frequency area is critical to the body of the sound. Players doing Metal
styles tend to cut this range out to create an aggressive sound, but if you
pull it too far back, the presence will disappear. If your EQ includes a
BANDWIDTH control, start with a one-octave setting. Use narrowband settings to
tune out annoying tones such as the low-frequency resonance of a guitar body or
snare drum.
- Enhancing Attack Many engineers assume that treble EQ is the best way to
produce attack. While its common to chase clarity this way, you can end up with
the treble cranked on every channel, and things will start to sound tinny. Try
using compression, which can control the attack and smooth out volume
variations at the same time. Adjusting the compressor's ATTACK control to slow
setting will let the sound's leading edge pass through, while the body of the
sound is reduced in level. This gives increased definition. A faster ATTACK
setting will clamp the leading edge, so the body of the tone will dominate. Set
the RELEASE control so that the compression cycle is finished by the time the
next note is played. With the right settings, you'll have a clear tone without
the added grit that sometimes comes with treble boost.
- Tighter Low end Compression can also do a lot to give the sound of the
bottom end more weight. The attack of a kick drum or bass guitar will get your
attention, while the body of the sound moves the air that you feel. Its worth
spending whatever time you need to get solid lows. You can build anything on
that foundation. If you fail, the track will never have power.
- Sub-Bass
Watch out for frequencies below 40Hz. They eat up airspace in the
mix and are too low to be heard on a many systems. An exception might be
5-string basses or HipHop drops that are designed to rattle the windows in the
car next to you. Even in those cases, much power comes across in the second
harmonic, from 80Hz to 100Hz. Many engineers roll off everything below 40 Hz to
make the mix sound cleaner.
Snare level Most tunes benefit from a strong backbeat. You can mix snares hot
because they are staccato, but they'll sound weak without enough low/mid body.
Try stepping on the initial peak of the sound with fast-attack compression,
and allow the body to come through as the gain control circuit releases.
Vocals Everyone loves air and vocal clarity, so 10 kHz gets boosted.
Consonants become more understandable, and you hear throat sounds. If you love
this feel, add a de-esser to your equipment rack. De-essers can control just
the excess sibilant sounds that lie in the 8kHz to 13kHz range, while leaving
the detail and body of the sound untouched. Add some low-ratio compression to
help the consistency of the performance, and you're 90% of the way to solid
vocals. The mastering engineer can de-ess the entire mix, but its always better
to fix a single track when possible.
Your Other Monitors
Every mastering engineer has faced disasters that can be traced back to good
people using bad monitors. It's tough to make good decisions if you can't
trust what you hear. I would never use loudspeakers costing less than $1000 a
pair as my only reference. Everything below that price point (and quite a few
above) are pretty severely compromised in some way. To make matters worse, most
speakers are not placed in the optimal location in the listening room, which
itself contributes more errors. In short, your speakers are lying to you,
especially in the bass frequencies. Only the truly massive processing power
between your ears is separating the truth from the lies. (Feel better? Didn't
think so...)
What's the solution? You could spend next year's mortgage payments on speakers
plus room treatment.... Or maybe not... So let's talk headphones! You
already have seven pairs in the studio for overdubbing, right? Forget them - we
need reference quality. I'll stick my neck out and recommend three fine
examples. Sennheiser HD600's, Grado RS2s, or my favorite, Stax Lambda Novas
with tube amp. Street price of maybe $330, $450 and $1500 respectively. Ouch!
Not cheap, but worth every nickel.
Listen to five minutes of good commercial music on any of them. Then one of
your mixes. The differences will be easier to spot with headphones. This is
because you have eliminated the room from the equation, and your ears are
hearing only direct sound. Plus all of these units are pretty accurate to
start with, down into the deep bass where mini-monitors never go. Think of them
as near-field monitors on steroids. You'll still need speakers to check
panning, since phones exaggerate the stereo image. And phones won't hit you in
the chest with your massive new bass tones the way that speakers can. But
they can be a magnifying glass for questions of balance and tone. You will
hear stuff that was lost through your speakers. And you'll have one more tool
for achieving the holy grail - mixes that translate well across many speaker
systems. By the way, HD-600s and RS2s have dynamic drivers, so they need a
strong, clean driver amp.
Mixing Techniques
Its easy to get overwhelmed when time is short and you have an album to mix.
Try slicing the work into manageable chunks:
- Create a short mix. Focus your attention on a section of the tune no more
than sixty seconds long. Include a piece of the main hook, part of one verse
and some of the bridge if possible. If you have a digital machine, set it up to
play back the section as a loop. Now work on the tones. Auditory memory is
short. There are times when you might want to loop ten seconds of music to
concentrate on the sound of one instrument.
- Start with the basic tracks. Bass, drums, one rhythmn instrument, and lead
vocal. Go for clarity and impact first. Work until your short section sounds
killer, then document the EQ, level and compression settings. You'll be able to
use most of what you learned so far on the remainder of the tune.
- Add parts one at a time. Resist the temptation to dial in all nineteen
awesome groove tracks and cool licks that the guitar and keyboard players
wrote. That is the way of the Dark Side. If you give in, you'll use up your
resources too soon, the mix will become dense and lose it's focus. There will
be less tension and release, which is what involves people emotionally in the
music.
- When the mix gets away from you, remember the silence. (Deep wisdom,
Grasshoppa.) All kidding aside, you want to hear the instruments clearly, so
become sensitive to that transition point where too many things are going on at
once. When you can't hear any silence behind the notes, cut away instruments
until the energy of the mix returns. In extreme cases, return to the settings
you saved before your ears and judgement became toasted. Take a break and try
again.
- Maintain sane levels. Don't record super-hot signals onto a digital mixdown
deck. With DAT and CDR, any level above -6dB means you have a 16-bit recording.
There is no advantage to pushing it harder. If the clipping indicator comes on,
you have already lost music. Try for maximum peak levels of -3 to -1, and let
mastering bring the volume up to commercial standards. If you use a
Finalizer/ Quantum/ Masterlink/ Maximizer /Ultramizer during mixdown, try a very few dB of
low-ratio program compression, to tighen up the sound a bit. If you use the
Crush-O-Matic preset and change your mind later, you may have to remix the
album to undo the damage. Fair warning.
Recap
If your mixes have a good sense of space, clear instrumental and vocal tones,
and energy that builds to a strong finish, the mastering engineer can spend
more time building on the strong points, less time fixing problems. The final
sound will work on radio, home and car systems, and everyone will be happy.
Have at it!
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