Close miking is a crucial technique for a majority of recording situations. Playing live in a bar, on stage singing or giving a speech, and even in the perfect acoustic environment of a world-class studio, close miking has it's place as one of the most effective means of faithfully capturing a sound source or instrument while keeping the signal as dry as possible.
Everyone has heard of this term. It's so common that people who have zero clue what they're talking about will offer up the solution:
"Just close mic it!"
But what does this really mean? Why was the technique developed? What does it offer over other techniques such as distance miking? How do we use it and when should we use it?
There are other microphone placement options, such as ambient miking to capture the sound of nature or a crowd as it responds to a performance. There is room miking to capture the distinct reverberation signatures of a specific acoustic environment. There are overheads used to create a stereo image, usually of a drum set or orchestra. There's even accent miking to accentuate specific tonal qualities, such as purposefully the neck of a guitar to pick up the sound of the finger sliding across the strings.
All of these techniques have their place, but they all usually piggy-back off of the extreme clarity and truthfulness of a microphone situated very close to the sound source.
Let's answer all of the questions above and get to the bottom of this advanced method.
And away we go...
It doesn't matter if you're using a dynamic mic or a condenser mic. It might be a ribbon microphone or a lapel mic. You might have one mic only in mono or an M-S orientation, or have two set up in an X-Y or A-B fashion. The goal and practice are one and the same:
Close miking is the practice of placing the microphone physically near the source of the sound being recorded, typically no more than 12 inches in distance away.
You might wonder why this is so prominent since you know about unintended consequences such as the proximity effect, capturing vibrations up even the best mic stands, or even electrical interference from specific instruments or amps. There's even the danger of a performer bumping into the mic. What gives?
There are two main reasons for using this practice:
That's pretty much saying "any time we don't want outside sounds getting into the recording." Which is most of the time. Even in movies if two characters are sitting on a park bench, they'll isolate each voice from the environment and then record the sounds of other people and birds and squirrels and all that separately.
Of course there are still times when you do want some of the ambience to be recorded, such as in a church cathedral. Other times you'll want to capture a blending of sounds such as several monks chanting together. There are times you'll want to provide yourself with options so you record the entire room or a distanced capture of a drum set or piano.
But for generally all other applications, you'll want to deploy your mic very close to the sound source.
Beyond the example concerning movies above, you will want to use this method any time you're in a position where:
To explain a little further, an electric guitar, bass, or keyboard, for instance can be plugged directly into a mixer. Even the cheap but good audio interfaces feature an high-impedance instrument input or you can use a D.I. box to convert to XLR. There are times where you'd rather output the signal through an amplifier and capture it again with a microphone though. And any source such as a human voice or acoustic instrument without pickups will require a microphone.
The key here is the third bullet point though. It's when you want the cleanest, driest, truest signal possible. The reason is that this opens up as many options as possible when it comes to mixing and mastering. This method manages to avoid having the sound of some idiot screaming "Freebird!" during your live recording. It avoids most standing waves, flutters, echoes, and reverbs in a room without acoustic treatment.
And most interestingly, even top of the line studios don't build isolation booths for more than vocals. So what happens when you have drums, bass, violin, and tambourine all in the same studio room, even with perfect acoustic treatment? You want to record each without the other bleeding into the mic. You use close miking with the right pickup patterns to get your isolation.
Life is all about choices in this give-and-take world. When you choose to employ the method of placing a mic this close to an instrument you trade one set of problems for another.
The first problem you should listen for is the proximity effect. That link has a full exploration on the topic.
The summary is that the closer the microphone gets to the source, the more of a bass response it exhibits. It starts around 125 Hz and goes down to below human hearing. As the mic moves closer this bass response can get as crazy as an extra 20 dB in volume. Radio personalities exploit this with specific mics and then compress the heck out of the signal to get that real fat, warm vocal sound.
But when you don't want to use this effect it's a problem that has to be equalized out of the signal and that can destructively interfere with the crisp and natural bass response of the source.
If you're using a close mic and a distance mic with the intention of blending the ambient recording into a mix, you can end up with the problem of comb filtering.
The name comes from the visual aspect of the phenomenon in which the extreme and regular dips in the frequency response look like the teeth of a hair comb.
What you have is constructive and deconstructive phase interference causing boosts and notches to form in the resulting combined wave from the two microphones. What's happening is that the distance between the two mics is conspiring with the speed of sound to create a mixing nightmare. You may think changing the distance between the mics will help, but it only moves the teeth of the comb.
One of those four will offer you your solution. The second option is typically the best when possible.
You know how in movies the director has that wooden clapper board where he'll say "Take 2, Action" and then snap the wood? That's so the mixer can align all of the different recordings based on that initial "clap" sound.
The Three-to-One Rule gets it's own special sub-section here. This 3:1 Rule helps you avoid comb filtering in the same way that dropping the secondary distance mic down in the mix by 10 dB or so reduces the interference and thus the intensity of the comb filtering.
The idea is that any other microphone being used near the close mic should be at least three times as far from the close mic as the close mic is to the source being recorded.
Envision a scenario where you're recording three vocalists as a group who need to sing live together to lock in their harmonies. You'd give each one their own close mic and have them stand a certain distance from each one, respectively. You need to make sure that the person on the left or right is at least three times as far from the middle mic as they are from their own respective microphones. Visually it looks like this:
It makes sure the bleed is at a low enough volume to not interfere with the main signal. Use your best mics as the close mic and save the lesser ones for the distance mics.
There's a few things you should be doing if you have enough time during your set up if you want the best recording.
Don't just set up and assume you're good to go. You could be getting the proximity effect or comb filtering. But worse, you could be wasting an opportunity to record the sweetest, most beautiful rendition of each sound source possible.
Throw some the best recording headphones you have on and have the instrumentalist play as you sweep the mic back and forth and up and down. Listen to how the tones change. Different frequencies will be accentuated and annoying ones will loose their muster. Try sweeping off-axis as well if any specific frequencies are popping too loud and you can't get rid of them.
You can imagine the impact it could make. Imagine an acoustic guitar. Sticking your ear right up to the hole in the body is going to sound boomy and resonant. Listening at the bottom of the neck is going to have a lot of string in it. Somewhere in the middle is likely what you want, but how would you know if you don't take the time to try. The same goes for all instruments, amplifiers, and anything else.
Any flat, hard surface could be your downfall. You might take the time to position each person on the stage in their own pocket and use cardioid pickup patterns to isolate each. But what happens if you're pointing the sensitive part of the diaphragm at an instrument that has a flat wall right behind it?
You'll still end up picking up the delayed sounds of the other instruments bouncing off of that wall. This especially matters on tiny stages like you find at bars where the band members are essentially standing on top of each other. This phenomenon is exactly how satellite dishes focus a signal at their own recording devices:
Imagine the red point is your microphone right at the focal point. You'll be recording sounds in outer space like this. A flat surface isn't convex like this, but it stands to illustrate the point. You'll hate yourself if you don't notice this before hitting the record button.
The energy of a sound wave, and thus the volume, follows the inverse square law. This means that as you double the distance between the mic and the source (and this includes unwanted sources like reflective walls) the volume will drop by an additional 6 dB. You then need to double it again to drop another 6 dB! If you double too many times you'll no longer be close miking.
The point here is that you need to take care with your pickup patterns and where they are pointing. Look beyond how the instruments are situated and what direction the mic is pointing, beyond the source to what's situated behind it. Watch out for those pesky flat surfaces!
We just mentioned that the amplitude of the wave drops by 6 dB as you double the distance. But with your mic being extremely close, less than a foot, you're talking about some pretty high energy levels. This is literally pressure pushing on the diaphragm of the microphone.
Mics have sound pressure level (SPL) ratings and you need to be familiar with them. It's a fact that you're going to set up some players and then each one is going to reach for their volume knob and turn up just a little bit, because they know better than you and want to outshine the other members. If they exceed the SPL ratings of the microphone, you're going to end up with distortion and clipping in the signal and they'll blame you (ridiculous and funny and sad).
Make sure you're not recording too hot at the source. You may not see clipping along your signal path but it's baked in right at the microphone. You have to make sure you're soloing and listening to each microphone as you go through the set up process. Keep checking in throughout the session as well. Not even the best preamplifiers can undo clipping at the mic (nothing can undo clipping. Once it's in there it's in there). Once you toss on some compression it's only going to sound worse.
My recommendation is to have a cheap digital SPL meter (the one above gets the job done) in your pocket during this phase of the game.
To continue your exploration of this topic, you should attempt to gain a more specific understanding of a real-world practical set-up.
The California State University, Northridge has a page describing how to close mic an electric guitar. There are pictures showing techniques such as centered miking, off-center, inside the amplifier's cab, and even from the back of the amp.
ProSoundWeb describes several techniques to use to achieve the feel of specific genres when miking an acoustic grand piano. Specifically they mention when and how to use mono mics, balanced stereo pairs, X-Y or M-S configurations with a bidirectional mic, etc.
RecordingMag has a nice write-up on one of the most challenging, sophisticated, and intimidating tasks for a recording engineer... miking a drum kit. Bruce Kaphan there talks about each drum piece, how he sets up the mics, and which mics he prefers on each.
And that's a wrap! Close miking isn't hard once you know the three main problems to look out for. The proximity effect, comb filtering, and reflective surfaces can ruin your day. The solution to avoiding all of these problems is to not be lazy. Use your ears when setting up, not your eyes!