Miking up an instrument isn't an easy thing. It's not like a digital camera where you point towards what you want to capture and then click. Super cool vacation photo! You might not end up with a great photo, but you can certainly make it better afterwards. Not to offend photographers, but in audio, if you have a lousy source sound from the beginning, you are going to end up with a lousy mixed sound in the end.
Photo by Pablo Albacete
Joel wrote a great introduction to microphones a while back where he talked about different types of microphones, their polar patterns and various specifications you need to keep in mind when buying your microphone. During the following article I'm going to continue on the path of the microphone and give you a great beginners guide to using your microphones.
Before I start, let me stress that in the end, it's all in your ears. Be experimental when you can, move the microphone around wearing headphones to find the so-called sweet spot of the instrument. But to make things a little bit easier, here are some general tips, industry standard work principles and guidelines.
1. Microphone Placement
There are three general categories of miking: Close miking, or spot miking, distant miking and finally ambient miking. Let me explain the differences.
Close miking is when you use your microphone, you guessed it, close to the instrument. Generally speaking, microphones are positioned 1 to 3 inches (3 to 10 cm) from the sound source. With your microphone really close to the instrument, you get a thick, tight sound that sounds, once again you guessed it, close.
Listen to the string accompaniment of Eleanor Rigby by The Beatles. Geoff Emerick said that he got the tight sound quality of the quartet by close miking every instrument, which was very unusual at the time. (Ref: Behind the Glass, Massey, Howard.)
By close miking you also carefully try to eliminate the reflections and characteristics of the room in which the microphone is in. Many home recordists use close microphone placement only because their rooms sound bad, and they want to be able to get the purest source so they can add whatever reverb sound they want later on. Again, check out another one of Joel's article where he gives you a few tips regarding how to make your room sound a little bit better when recording vocals, and also check out one of my articles on how to makeshift a vocal booth in your bedroom.
There has to be careful considerations put into the position of you microphone when close miking. Putting it too close to a specific spot on an instrument will only capture that specific characteristic of said instrument, like taking a picture of a tall building holding your camera in landscape view. You either get the top, or you get the bottom. No super cool vacation photo that time.
The same applies to instruments that are rich in harmonic content, i.e. instruments that have a big and lush sound. It's hard capturing the full body, depth and bigness of an instrument using only one microphone, especially when it's close to one specific part of the body. That is when you have to resort to either using more microphones, which I'll get to later, or mike up at a distance.
Using distant miking, you pull yourself a little bit farther from the source sound. Generally considered, microphones are placed at a distance of 3 feet or more(1m or more) from the instrument. By placing the microphone farther away you capture the full tonal spectrum of the instrument. In contrast to close miking, distant miking picks up the whole instrument instead of just a small part of it.
By putting your microphone at a distance you are also picking up a lot of the room sound you are recording in. The acoustics of the room get mixed in with the sound of the instrument, resulting in a live acoustic sound. If you have an amazing room, this doesn't need to be a problem because the natural acoustic amazing-ness of the room only enhances the sound.
But, as I said before, many rooms tend to sound bad and only interfere with the sound of the instrument, putting an unwanted room sound on an otherwise great sounding instrument. So try experimenting with distance, walking around the room finding a good spot where you can hear the instrument well.
Ambient miking is the technique of putting your microphones at a distance that it almost only picks up the natural reverb of the room you are recording in. Sometimes it's even at such a distance that it's not even in the same room.
Say you are recording a drum kit in a tight sounding room but in the hallway outside the studio the drum kit sounds live but distant. By putting up ambient microphones in the hallway you are capturing the drum kit, but you are essentially picking up the reverberations of the hallway leading down from the studio room into the microphones.
When somebody puts up room mics, they are essentially miking up the ambience. Room mics can be put in the corners of the room, where they pick up the overall sound of an orchestra for example, or the room sound of a string quartet.
Ambient miking, mixed with close miking can give you the best control over the sound of an instrument. This gives you individual control over the spot mics, and over the room. Think of it as having two tracks in your DAW (Digital Audio Workstation, e.g. Pro Tools, Logic Pro etc), one for the instrument (the spot mic) and one acting as the reverb (ambient mic).
Also, if your microphone has different polar positions you can experiment with switching between them, listening to which one sounds best. This doesn't only work with ambient miking, but distance and close miking as well. A figure eight pattern close miked can give you a tight sound from the closeness of the instrument, but also a live sound from the reflections of the room.
Photo by Pablo Albacete
2. Which Microphones to Use in Which Situations
You can use all kinds of microphones for spot miking. It just depends on the instrument you are recording and the sensitivity of the microphone in question. Using condensers and ribbons for full-bodied acoustic instruments such as cellos, acoustic guitar and the sort will give you better results than using dynamic microphones that cannot capture the full acoustic quality of these instruments.
Dynamic microphones serve really well when it comes to very loud instruments like drums and distorted amplifiers due to the amount of noise they can pick up without distorting. You can easily put a dynamic mic up to the grill of your Marshall stack without thinking twice about it, but putting a ribbon microphone against a distorted, high volume amp is probably going to destroy it.
Distance & Ambient Miking
When you move a microphone farther away from an instrument, you will need to increase the gain on your pre-amp in order for it to pick up enough volume. The sensitivity of condensers and ribbon microphones means that they need less gain to accurately capture an instrument at a distance.
What this means is that unless you have a really noisy instrument, like drums or high-gain amplifiers, you will need to use condensers or ribbons. Dynamic microphones just lack the sensitivity, frequency response and gain to be able to effectively pick up and instrument at a distance.
3. Combining Microphone Positions
The most effective way to capture the full sound of an instrument is using various microphone positions, each one capturing a different tonal quality. This can include using all of the various distance miking techniques, having one microphone close to the instrument, another one picking up the a little bit of the room and then a third one acting as a natural reverb.
Example, when miking up a double bass you can put a spot microphone close to the body, aiming to capture the sound of the fingers slapping against the strings, another mic at a distance of a few feet capturing the low end, and a third one picking up the bass in the room.
Another way of using different miking positions is using a few close mics, and then one for the room. Consider using a few microphones at different positions around an acoustic guitar for example. Put one one by the sound-hole, another behind the body and a third one picking up the frets. These three microphones, although close to the same instrument are picking up radically different aspects of it. Mix and match these to get a great full and tight sound, and then add another one at a distance for yet another color.
Having a good basic understanding of microphone techniques is crucial to getting a good sound. The age old adage goes, (expletive deleted) in (expletive deleted) out. You can go a long way by using these techniques, setting up microphones where they are “supposed” to be. But the first and last tools at your disposal are your ears, so trust them rather than a diagram with inches, meters and feet.
If an instrument sounds better to your ears when you break all the rules, then fine. If that's the sound you are looking for, you found it. General microphone techniques work most of the time, and get you at least halfway there. The rest is up to your ears and taste.
(Reference: Modern Recording Techniques, Huber, David Miles. Runstein Robert E.)