Summery: Here I take a look at the effects of choosing different mics and mic placements on an acoustic guitar. I give my two cents on what to avoid and how to get a particular sound. So you don’t have to take my word on it there are audio examples.
Background: Recently I was asked to track acoustic guitar for a project. Over the years I’ve never been quite happy with my acoustic recordings. One is too boomy, one has too much ringing mid-range, another sounds tiny and thin. I think acoustic guitar is one of the harder things to record. The sound is complex; quick string attack, boomy guitar cavity, and 6 strings resonating interactively. No wonder there is no decent acoustic guitar sim or pickup system.
Imo pick strummed acoustic guitar is the hardest to get a good sound from. I’m not sure why. Perhaps because everything is sounding together. It’s a real balancing act with all those components.
I listen for things I don’t like and then minimize them. It’s a subtractive process like most eq decisions. Here are some of the things I don’t like to hear and how to minimize them.
I’ve taken my typical semi-scientific approach below. I try to keep all variables constant except the one I’m interested in. So same guitar, same pick, playing in same area of room. Just changing out mics and mic placement. No processing was applied.
Pick-click: There might be an actual name for this. There might not be. I’m talking about the high pitched metallic clicks due to pick attack. Because these are so bright and loud they tend to make the guitar sound tiny or thin. Imo they don’t add much musically. I can’t think of a time I ever wanted them in a recording. This is what I’m talking about. Here is a condenser mic about 12″ in front of the sound hole.
Picks do sound different. So at first I tried using different picks. It wasn’t much help. The click was still there in a different flavor. Now… all my picks are plastic. Perhaps there is some magic tortoise shell out there that sounds better. Sadly, plastic is all I’ve ever known.
Next I tried something I knew would work. If the mic doesn’t see the pick the click should be reduced. High frequencies have a hard time rounding corners and they are absorbed easily. So I placed the mic where the diaphragm had no line of sight to the pick. Here is another example. It’s the same condenser placed behind my left ear like this. Check out my serous mic-placement-face.
As you can hear the combination of my fat head and the body of the guitar acts as a baffle and greatly diminishes the “click”. The overall sound is also very different. I’d say smoother even phase-y-er.
Lets say you don’t like the new sound. You prefer something that sounds more direct and close. You could keep the old placement and swap in a less sensitive mic. Here is the same placement (12″ in front of sound hole) as the first example with an sm7.
We all know we should use a large diaphragm condenser to capture the details of an acoustic guitar. Think about un-knowing that one. I like me some durable dynamics on the a-guitar.
Ringing Mids: Like I said recording acoustic guitar is a bit of a balancing act. I tend to like the guitar to sound open and warm. Totally meaningless terms. I know. What I don’t like is ringing… um resonance in the mids. For one these can mask the vocals. And they give the acoustic an AM radio quality.
I recommend taking a mic and listening to the body of your guitar at different places. Keep the mic about 3″ away from the wood. Then record the back of the body, the top (front) of the guitar, the end of the guitar, the top between the sound hole and 12th fret. Just get a good sampling of the way the wood sounds at different positions. All the wood on the body is vibrating and it all sounds different.
Most of the volume of the guitar is coming from the sound hole but the wood on the body also contributes. So I see it as a combination of the sound hole and the nearby resonating wood. If you record the back of the body you get a lot of the wood resonating and the sound hole indirectly. If you record the sound hole at 4” you get mostly the sound hole and a bit of the top resonance. This was confirmed by all 4 mics I tried out. At 12” or less in front of the sound hole the sound was open in the mids. As I moved the mic further back they picked up more of the top resonance and the mid-range got cluttered.
Here are some examples.
12” and 24” from sound hole with Rode NT1-A
4” and 12” from sound hole with a SM7
4” and 12” from sound hole with a SM57
4” and 12” from sound hole with an RE-20
This is a theory. But even if it’s not right I think you can hear what I’m talking about. The mids, for whatever reason, are getting more resonant as I move the mic back.
I know we’ve all read not to mic the sound hole but it sounds nice to me. That brings me to my next point.
Don’t Mic the Sound Hole: It’s too boomy. This is easy to hear if you just record a bit at 4” in front of the sound hole and then move the mic over a bit and record at 4” from the top. Like this:
4” in front of sound hole RE-20
4” off the top (between sound hole and end button) with RE-20
I think this example gives some weight to my theory. The recorded sound is a combination of resonant body wood (the top primarily) and what the sound hole projects.
K. Too much bass (around 100hz) can definitely be an issue come mix time. Typical rock has a strong bass and kick down there. A lot of times the acoustic guitar is high pass filtered. It’s there but all the warmth is gone. It functions like a hi-hat or cymbal. If you don’t filter the acoustic guitar it muddies up everything and eats up head room.
So what to do? I can’t tell you that. I’ve heard boomy guitars work in sparse mixes. I’ve heard tiny jangly ones work in other songs. What I want you to hear is how to get these tones. Hopefully I’ve done that. Maybe instead of buying that $1,000 a channel preamp or that fancy new condenser mic you’ll experiment with a workhorse mic and it’s placement. Take your best guess, record, then listen in the mix. Rinse repeat until you get what you want or your hair falls out.
Noise: The trick with noise is getting an acceptable signal to noise ratio. The noise comes from your room, your mics, and your pre amps. The signal in this case is your guitar. acoustic guitar can be very quiet when played softly. This makes the signal to noise ratio a lot smaller and suddenly you start hearing your computer fan or how noisy your mic is.
Speaking of noisy, here are 2 mics I have. I held everything constant except the mic so what we’re hearing is just the difference in a mic’s self noise.
I think it’s important to take a critical listen for noise when recording. Compression will only make it worse latter. Things like eq and noise reduction plugins can be used but they process your signal too. It’s a game of “acceptable degradation”. Try and get it right upstream.
What can you do to limit noise when recording a quiet acoustic guitar?
- Swap in a preamp or mic with less noise.
- Some very low frequency noises (traffic rumble) can be filtered without affecting the sound of the guitar much.
- Most microphones are directional and will have a place in their pickup pattern where they are least sensitive. This point should face the offending noise such as a computer. It’s worth listening and moving the mic to find where it rejects the best.
- High frequencies are directional. Put a baffle in the line of sight of the mic and the offending noise.
- You can move the mic closer to the source increasing the source volume but this will change the way the source sounds. I prefer to place the mic where the source sounds best. I’ll take good tone over some noise any day.
- Lot of things can be turned off while recording. For example my whiny scanner and guitar processor with cooling fan.