The Awesome Guide to Acoustic Guitar EQ
Before we talk about the specifics of acoustic guitar EQ I want to make sure you're approaching equalization with the right frame of mind.
Picture the scene - your living room has become a home studio for the day. The drum kit is out in full (and the drummer seems to have gained five more cymbals). The bassist finished setting up hours ago and has been waiting patiently. The singer is late (no change there) but you've already set up a mic for them. You know their voice, and have picked the right microphone for the job.
You're playing acoustic guitar. A pair of small diaphragm condenser microphones hang in the air in front of you. After countless trips between your computer and the mics, you've got the exact sound that you want. The seemingly endless mic tweaking was worth it. The guitar sounds full, wide and natural.
Your singer arrives (semi-drunk) and you blast through a song with the full band. The first take is perfect - awesome! You lay down a few more just to be safe.
Next on the agenda: a chilled acoustic piece. Just guitar and vocal. BUT here's the catch. You don't move the mics. Why would you? It sounds great already.
Context, context, context...
As I'm sure you can imagine, you don't want the acoustic guitar to sound the same in these two different songs.
In a full band your guitar is just a single part of a larger sound. Yet in the acoustic track your guitar is the only instrument playing. This is where equalization comes in. With a bit of EQ, we can completely change the sound of the acoustic guitar.
Microphone placement and guitar tone are the key factors in getting a good sound. This is where you should concentrate 80% of your effort. But we can use EQ to add interest, fix problems, remove unnecessary frequencies and improve the overall sound of the guitar.
Let's start with some general tips. After that I'll cover each frequency band that we want to address separately and in detail.
Assess the situation
While we're on the subject of context, this may as well be the first tip. The way that you shape the tone will depend entirely on the song, the guitar and the arrangement. If it's a full band piece, don't mix with the guitar solo'd. Instead, EQ the guitar with everything else in.
You don't want it to sound good on it's own, you want it to sound good in the context of the song. If it sounds slightly odd or unnatural when you do solo it, that's fine. It doesn't matter. We're not going for a natural sound in this situation - we just want it to <a href="http://www.homestudiocenter.com/make-instrument-and-vocal-sit-in-the-mix/">sit nicely in the mix</a>.
On the contrary, if it's a solo acoustic piece (or a small ensemble), you want the guitar to sound as natural as possible. Be very conservative with your cuts, and be tasteful with your boosts.
Cut everything below 100hz (at least)
Use a high pass filter to get rid of everything below 100Hz. If you want to hear what you're cutting, put a low pass filter at 100Hz and have a listen. It's all boom and rumble. You don't want any of that! Experiment with the frequency of your high pass filter. Feel free to bring it all the way up to 400Hz in a band situation (if it works).
That way it won't conflict with the bass, guitar, kick or vocals. More on this frequency range in the next section of the guide. I just wanted to emphasize this one tip. It's stupid-easy to implement and will clean up the guitar in an instant.
How to deal with pickup and DI recordings
Was the guitar recorded direct from the built in pickup?
It's not ideal, but don't panic! A microphone will always sound better - when there's not too much noise.
In a live situation it's a good idea to take a feed from the guitar as well (if it is an electro-acoustic, that is) in addition to a cardioid mic positioned in front of the guitar. In some cases, you might not even be able to chuck a mic up.
Using the pickup alone can cause some issues, though. First, it doesn't sound as full or natural. You lose most of the body and bottom end. Secondly, the strings and mid-range are heavily emphasized.
But with a bit of subtractive EQ we can reduce the "quack" and "honk" in the mid range!
If it's a magnetic pickup, try cutting around 500-600Hz and 2-3kHz.
If it's a piezo pickup, try cutting around 3-4kHz.
Here's something else you can try if you're not happy with the sound. Universal Audio make an awesome plugin that turns your pickup recording back in to a full acoustic guitar (sort of). It's called Sound Machine Wood Works. Have a listen and see what you think.
If you have a pickup signal as well as a mic signal, consider using the signal from the pickup just for some clean bass frequencies, this will add a fuller sound compared to just the mic signal. To do this, cut the frequencies from the pickup below about 70-80Hz and above about 500-600Hz. Keep the volume of this track quite low compared to the mic signal.
Use frequency slotting
Muddiness is a common problem. Most of the instruments in a typical band are centered around 200-300Hz. This is another reason to bring your high pass filter all the way up to 250-400Hz.
Alternatively, cut everything else around 300Hz to give the acoustic guitar some room if it's a small ensemble.
If it's a piece with just acoustic guitar and vocals, try cutting the guitar around the fundamental of the vocal to give it some room. Use a frequency analyzer to find the fundamental of the vocal (it will be the highest peak). It will be around 100-180Hz for males and 170Hz-250Hz for females.
Before you start equalizing your acoustic guitar recording, be sure to remember these EQ best practices.
Try to stick to subtractive EQ. Boosting frequencies can mess with the phase of your tracks. When you do boost, be subtle and use a wide Q (bandwidth). When you cut, go narrow.
In general, you want to cut frequencies to make something sound better. Only boost frequencies to make something sound different.
If you have a stereo recording, check the phase by soloing both channels and switching your output to mono (or just temporarily pan them both to dead center if that's easier).
If you notice a drop in bass, you probably have some phase issues.
Zoom in and see if the waveforms line up. If not, ditch one side or try to move them in line with each other.
Don't forget that everything in this guide is just a starting point and a guideline.
Always trust your ears and experiment. If it sounds good, it is good!
Mostly rumble. Above 80Hz, some fullness.
If it's an ensemble, cut it. Simple!
It it's a solo piece, you could leave in 80Hz and up for fullness.
This where the vast majority of the energy of the instrument lies.
The 100-150Hz range will contribute largely to boominess, so cut here if that's your problem.
If the guitar sounds muddy, be liberal with your cuts between 150-400Hz. Especially 200-250Hz. That's the most problematic frequency range.
Cut this if you recorded using the magnetic pickup on the guitar.
If you currently have cheap strings on your acoustic, cutting these frequencies might help the tone.
This is where you'll find the "bite" and "presence" of the guitar.
A subtle and wide boost across this frequency range can help your guitar stand out in the mix.
On the contrary, try cutting some of these frequencies to make the guitar more subtle.
Within this range, remember that you can cut 2-3kHz to make a magnetic pickup sound better, and cut 3-4kHz to make a piezo pickup sound better.
This range contributes to the "sparkle" of the guitar.
Experiment with subtle boosts, or reduce these frequencies to make the guitar sound warmer.
Most string and finger noise is around 10kHz as well.
This is where the "air" is.
I like to add a subtle 1 or 2 dB boost with a high shelf around 10kHz upwards.
Increase these frequencies to make your guitar more audible to dogs. You won't be able to hear the difference, but your pooch will thank you.
Just kidding :)