Articles / Mic Intro
An introduction to microphones
by Muied Lumens
Microphones have to do a very tough job. They have to mimic not only the amazing evolutionary product we call "ears", but also the accompanying brain that interprets the signals coming from those ears. While there is a whole field called Psychoacoustics that deal with the complex and not fully known process of how we percieve sound, thankfully mikes do not (yet) have much of a brain of their own, so understanding them is a little bit easier. Technology has not had millions of years to develop into what it is today, but it still does a pretty good job if you know a thing or two about how things work. Getting more or less predictable results from microphones is directly related to three major factors; what the source is, which type of mic you use, and where you put them both. That's it, in broad strokes, so lets get to it!
Everything starts with the source, and if this is good then you are off to a great start, and in many ways you have already won. For example, a great musician poorly captured will still sound good to a large extent. You never know though, so it's better to record than regret. The nature of the sound source and its volume will decide how you place your microphone and which type you need for best results. As you gain experience you will be able to make better decisions before you start.
Long story short
For music purposes, there are two main categories of microphones - dynamic and condenser (or capacitor). There are many others, but these two are the ones you are by far most likely to encounter, so we will treat any other type as "speciality" mikes in this article and almost ignore them completely. If you are looking to buy your first microphone, this is the distinction you will need to worry about. The other main thing about a mike is its directionality, or Polar Pattern. This simply means where it picks up sound from - not all mikes are equally sensitive in all directions. These factors determine how a mike records the environment it sits in, and knowing these will help you decide which mike is better for your intentions.
Dynamic microphones are typically used for live vocals and instruments, and are in widespread use on the stage. The reason for this is that they do not easily feed back because they pick up sounds most efficiently when placed close to their source, and are usually directional so they reject sound coming from behind them, from a monitor for example. They also do not require any power and are simple in build so they should take quite a beating. On top of all this they are also fairly resistant to humidity and are therefore perfect for vocals. If you have a dynamic mic be sure to place it very close to the source you want to capture. You are therefore more limited with these.
Condenser mics are better suited for a "studio" environment because they are more sensitive to shocks and humidity, so treat them with care. They are in general more efficient at picking up sound and need to be powered via phantom power (so called because it uses the same cable for power as for sound) or batteries. They come in all shapes and sizes and have different caracteristics, so this is a huge topic. I will however give you a short version which won't be accurate at all but will give you a general idea.
There may be many arguments against this, but if you were to have only one mic for everything you will come up against, you could do worse than getting a small-diaphragm condenser mic. These are usually long, thin and cylinder shaped and have a fairly neutral sound compared to large-diaphragm mics. The diaphragm refers to the membrane that actually captures the sound waves and converts them to electricity. The larger the diaphragm, the more coloured the end result will be, which is not a bad thing, it's just a matter of choice. Mics are often chosen for their specific character, not for being neutral. However, a neutral mic would be better overall for multiple tasks and more predictable results.
All mics have a directional bias, also referred to as their "polar pattern". Some are almost without directionality, which means that they capture sound equally from all directions. These are called omnidirectional mics, and are normally used in quiet conditions since they easily pick up environmental noise. In a huge cathedral they are useful because they capture more of the reverb, as well as the source. Likewise with ambient soundscape recordings. If you want to make sure you get everything these are the ones to go for, but they tend to be hard to control in terms of what you want to capture and what you don't, so placement becomes more important. Onmi mics do not suffer from something called the Proximity Effect, which means that there is a bass rolloff as you get more distance between the mic and the source. This way, omni mics may sound closer to what you actually hear in real life, but it is not a given.
By far the most common type of directionality is the cardioid, or simply "directional" mic. It is more utilitarian because you can aim it at something and it will reject other parts of the sound, unlike the omni mic. It will in particular reject sound coming from behind it, which makes it a little easier to set them up. Simply point it towards what you want to record, and away from what you don't... at least in an ideal world.
There are a lot of other types of polar patterns, like hypercardioid and supercardioid which means they are even more directional than cardioid. Bi-directional mics (often ribbon mics) pick up sound from in front and behind them equally, but the sound behind it will be phase reversed. The list goes on... Also there are many mics where you can change the directionality with a switch or by swapping out the capsule. You should be safe enough with just a cardioid pattern for most uses.
This is just as important as the mic you use, and there are a few things to keep in mind. First of all, a good mic position requires you to use your ears critically and you can only do this effectively after a bit of experience. Practice makes perfect, and it is a good idea make a note of how each setup was done for when you listen back so you can decide what the end results are from each of them.
It may seem obvious, but the closer you are to the source, the louder it will be. This means that everything else, like background noise and the reverb of the room will be softer in relation. Also, if you have only one mic, this is an efficient way to mix multiple sources in one take - and indeed this was how music was recorded way back before anyone had even thought of multitrack recording. Musicians would be placed in a room around the mic and the mixing was achieved naturally by how close they were to it.
The room you are in
Where you are will greatly influence the whole feel of the recording, even if you are up close. Again, in very broad strokes, the smaller the room, the more complicated things will be, especially in the lower frequencies. You can dampen frequencies by using all sorts of soft surfaces like pillows, duvets and carpets, but to dampen low frequencies you really need proper, dense material or a great amount of luck. You can also do the opposite, which is to "liven up" a dead or dull sounding room, by placing some reflective material like wood or hardboard in a strategic position, like over the carpet on the floor. Remember that sound waves bounce off flat surfaces in a similar manner as light does, so imagine a mirror in the position you want to dampen or liven up.
Careful mic placement means that you can some times get away with murder even in a small room. Without going into details about acoustics, one aspect of it is useful to know, referred to as room nodes, or standing waves. You can hear these in action in a small boxy room by playing a sine wave (50-100 Hz, try a few different ones) through a single speaker and moving your head around the room. You should hear the tone rise and fall in volume as you do so, and maybe even make it disappear completely in a certain position.
If you can find a spot where it sounds good, place the mic there. You may have to fine tune the position a bit, as your own presence will make a difference in the room too, at least if the mic is fairly capable or the room is tiny.
If you are unsure of what you are doing, stay with mono until you do or get a dedicated stereo mic. There are many types of stereo mic techniques, too many to start listing here and I consider that beyond the scope of this article. Stereo is obviously useful for wide, panoramic sounds and ambiences, amongst a lot of other things. There are a lot of portable recorders with built in mics that are handy and good sounding, and to my knowledge, all stereo. You can find out more in the recorder thread in our field recording forum.
Getting a mic that will give you good results is not an easy task, but in general the law of diminished returns apply. A cheap mic will probably sound OK (i have two chinese-made small-diaphragm condenser mics that cost peanuts, and get good results from them), but if you invest more, the sound and build quality will be noticeably better, until you reach a point where it makes little difference unless you run a high profile studio. If you are unsure, just get what you can afford and use it with the utmost of care (as outlined above) and it should last you a long time.