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Mic Preamps, Gain Staging, and EQ

Written by Willie Green. Published: Friday, April 23, 2010.

Mic Preamps and Gain Staging

One of the most overlooked elements in home recording is the mic pre. It’s far more than the knob you turn up to make your mic work; it’s a very important part of your vocal sound. A quality preamp can have a lush, warm sound or be crystal clear; it’s a critical component to the tone of your vocals. A sub par pre (like the preamps in an MBox) can sound dull, lifeless, and distort easily. All designs will sound different, this is something where you’ll want to listen to a few different models before you buy something.

Although there are countless preamp makers and designs, the two basic types of preamp you’ll come across are solid-state and tube.

A solid state mic pre is the basic design; it provides variable gain to boost the mic signal to something you can work with. A tube preamp does the same thing, but includes a vacuum tube which can add more character to your sound. That character is one of the most over-described terms in audio, the best was I can describe it is “warmth” but you’d do well to listen and describe it for yourself. Regardless of which type you choose, you’ll want a preamp that provides a detailed sound, and one that has a wide dynamic range – meaning you can crank it up for quiet sources, (without a lot of inherent noise) but also one with enough headroom that a loud source won’t quickly distort it.

This is where gain staging comes in. Gain staging simply means maintaining proper levels throughout your recording chain. Good gain staging will keep you from distorting your signal and make sure you have good healthy recording levels. As discussed last month, the first step is to have your mic the proper distance from the vocalist/instrument – positioned to get the sound you want without being too close as to cause overloading. The main thing to remember: once you record distortion, it is very difficult or even impossible to remove afterward. Nothing is worse than getting the perfect performance, but having it ruined by a recording mistake. It isn’t always that easy to capture again.

Channel Selection You want good levels on your preamp, but with enough room to spare in case your vocalist decides to get louder. There are a number of reason to make sure your levels aren’t too low however. First, every piece of gear has inherent noise, and you want to get your levels up far above the noise floor so when you process later on, that noise isn’t an issue. Second, your digital converters, software and plugins sound better with healthy signal. They’re designed to use up to 24 bits of resolution, so in theory, the more of that dynamic range you use, the more accurate and therefore, better-sounding, they will be. Your mixes will thank you for providing good level throughout.

You don’t want to be too loud though, digital distortion is not a pleasant sound and you want to avoid it at all costs. That popping and cracking is nothing you want in your tracks. If you keep your peaks around -3 or -4dBFS you’ll be in good shape. (the meters in your recording software are in dBFS, with 0 being the point of clipping).

Next month: Vocal Tracking

EQ

EQ is one of the most common audio processes, and simultaneously one of the most abused. When something isn’t sounding right, this is always the first knob/parameter that folks reach for. It can certainly be used to correct problems, it can also cause more than it fixes.

In a perfect world, you would need very little, if any, EQ. If the right mic was used with the right mic pre, your audio will sound great and need very little adjustment. You could just throw your faders up, get a nice balance and call it a day. As your recordings get better, this will get closer and closer to being the case. But if you need correction, before you reach for that knob, try a couple techniques first.

Panning – If you have two sounds that are overlapping and thus becoming muddy, two guitars for instance, pan them opposite each other. (However, be careful with low frequency sounds like basses and toms panned to the sides. It will pull the focus of your mix from the center)

Levels – Everything doesn’t have to be so damn loud! If you’re getting a build up in certain frequencies, turn one or more of the instruments down. Great music has dynamics and depth, part of what makes the loud parts exciting is the contrast with the quieter ones.

If these simple tricks aren’t cutting it, then it’s time to pull out the EQ. Keep in mind that like all other gear in the audio world, EQ’s have their own sound. Some, like a Pultec EQP-1A are going to impart a big sound even before you touch a knob. Others will be extremely neutral sounding and are used for surgical fixes. This is why people will have a selection of EQ’s, use the right tool for the job.

Pultec EQ

A few quick EQ basics.

There are four basic types of EQ:

-Fixed – The most common, similar to what you’d see on your home stereo or a DJ mixer. A few manufacturer set frequencies, you can only boost or cut.
-Graphic – This is what you might find on high end home stereo systems, anywhere from ten to thirty (or more) EQ bands, but again only boost or cut.
-Semi-Parametric – What you would find on all but the smallest Mackie mixers for instance, set High and Low bands with “sweepable mids,” allowing you to choose what mid frequencies you want to affect.
-Fully Parametric – This is the most common EQ to find in software, like the Waves Q10 or the standard DigiDesign EQ. They will have multiple bands, and you can not only choose they frequency each band effects and the boost or cut, but also how wide a range you effect. This width is called the “Q”. The higher the Q number, the narrower the frequency range. You an also choose a High or Low Shelf, which will boost or cut anything above or below the selected frequency.

The first, most important rule of thumb – CUT BEFORE YOU BOOST! Read that sentence again. If you find a sound to be muddy, cut some of the lows before you go boosting the hell out of the highs. Cuts sound far more natural than boosts, this will keep your tracks from sounding plastic-y, especially if you don’t have really expensive high end EQ’s. If your song is sounding really boomy, and you have two instruments in the same frequency range, notch some low mids out of one, (or both if need be) and your mix will clear right up. This is especially effective for kick drum and bass. These should work together, not battle each other for the same space. The magic frequencies for this are around 250 -300Hz. That’s where the mud in your mix is, pull some of that out, and your mixes will be nice and clear.

Rule of Thumb #2 – Just because it’s rap music doesn’t mean you need obscene amounts of bass. Lots of bass doesn’t automatically equal a good hip-hop mix. Of course you want your music to knock/bang/whatever, but you want your bass clear and balanced, not just loud. Unbalanced, overly-loud bass can also wreak havoc with any mix buss compression, which we’ll discuss next month.

Rule of Thumb #3 – If you hear a problem, but don’t know exactly what frequency it is, sweep. This is the beauty of a parametric EQ. Pick a band, and a relatively narrow Q, and boost it quite a bit. (Don’t do this with the speakers cranked, you’ll regret it) Now sweep through the frequencies, and when you get to that problem spot, it will jump right out at you. Now cut that frequency, adjust your Q so you’re only effecting what you want, and you’re good to go.

Filters also fit into the EQ category. (Well technically, EQs are filters, not the other way around). While often used in creative fashions, filters are terribly overlooked tools. Filters cut at a much sharper rate than your average EQ, and are used to eradicate any offending frequency. Use filters and shelves often, especially if you use a lot of samples and/or drum sounds grabbed from vinyl. Quite often there will be low end rumble, possibly even that your ear can’t hear, and trust me, it’s messing up your mix. That low end energy is causing your speakers to work overtime, and making them less accurate with the sounds you actually want there. That low end in your shaker track isn’t helping anything. Put a high pass filter on that and make space for the low end you want. Basically, if you see your woofers moving and going crazy, you have offending low frequencies.

Next Month: Compression Pt. 1

Listening

Check your mixes where you listen to music on the regular. Just because your mix sounds fantastic in your studio, doesn’t mean it will translate to other speakers. I listen to most music on my iPod on the train. Some people always hear new records in their car. You might have a shower radio you listen to every morning. Listen on these systems as well, this will give you real life perspective of your mix, and you can directly compare to records you know.

Willie Green
www.WillieGreenMusic.com

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Willie Green is an in-house producer for the Brooklyn-based Backwoodz Studioz record label, and a freelance mixing and mastering engineer. The Berklee College of Music graduate has also managed a number of recording studios throughout the Northeast.

Category: Columns, Pro-Logic