Microphones are like people: each has its own distinct personality. So choosing one isn’t a matter of which is “best” but rather which gives the desired result for a given purpose. In fact, unlike other gear, where frequency response should always be as flat technically possible (what goes in is what comes out), mics are often chosen because of the way they color the sound of what’s being miced.
Studio engineers develop their mic-choosing skills by listening to a lot of different mics on a lot of different instruments. Home recordists don’t have that luxury. What we can do is look at the mic choices typically made by professional engineers for various instruments, try to understand why those choices seem to work well most of the time, and apply what we’ve learned to mics that are within our budget. To do that, it helps to start by understanding a bit about some basic technical concepts.
Types and Specs
The vast majority of mics that are relevant to home recording fall into one of two types:
Dynamic mics use a thin membrane (diaphragm) attached to a metal coil in an electromagnetic field. When the diaphragm vibrates in response to sound waves, the movement of the coil converts the waves to electrical energy. A variation on this concept is the ribbon mic, in which the membrane and coil are replaced with a thin metal ribbon.
Condenser mics use a diaphragm as well, but in this case the diaphragm acts as one of two plates in a capacitor. The mic is powered (batteries or 48-volt “phantom power”), and when sound waves cause variations in the distance between plates, the electrical energy output from the mic varies as well.
Dynamic mics are known for their durability (except for ribbon mics), which makes them great for stage and road use. But they are also used in even the highest-end studios when the character of an individual model is a good match for the instrument being recorded. Condenser mics are generally flatter across a broader range of the audible spectrum and more sensitive to minute detail, especially the highs that give a sound “air.” The result is typically described as more “transparent,” meaning it sounds more like you are listening to the original sound of the instrument itself.
Underlying subjective terms such as “air” and “transparent” are the objective measurements that make up a mic’s specifications. Specs should be taken with a grain of salt, because manufacturers don’t all take their measurements the same way. But if you take a little time to understand them, you’re repaid with some insight into why different mics sound the way they do. A great place to start is the Microphone Data site sponsored by Rycote, which includes an advanced search feature to find specs on mics meeting specified criteria (e.g. “condensers under $500″).
The other key spec is frequency response, which tells you how well the mic picks up the various parts of the audible spectrum, ranging from the lowest bass rumble to the highest cymbal overtone (and beyond). On Microphone Data this is given as a number and also as a graphed curve for each polar pattern, which is far more informative. When you look at these curves, you’ll quickly realize that few mics are actually flat by the standards we would apply to other types of gear like consoles or recorders. Once again, unlike other recording gear, mics are generally chosen for the way they color the sound rather than for how little they do so.
Mic Like the Pros
So how does all this background info actually relate to choosing mics? Let’s start by assuming that professional engineers have a pretty good idea of what they’re doing, and see what we can learn from what they typically do. Drum kits make a useful example because they encompass a wide range of different types of sounds.
In a classic studio setup, the drums themselves are typically miced with cardioid dynamics. Shure® SM57s, which have a notable “presence” peak in the upper midrange and roll-off in the lows, are often used to give snap to the snare. Sennheiser® MD421s, which also boost high-mids but combine that with a fuller bass response, are a standard choice for toms. And the Electro-Voice® RE20, which is flatter overall (less presence boost and more low end), is a top choice for kick. In each case, the strengths of the mic complement the character of the instrument being miced.
For cymbals, cardioid condensers rule. Small-capsule condesers like AKG® 451s are often used for hi-hats. They are also among the common choices for overheads, as are large-capsule AKG 414s and Neumann® U87s. What these and similar condenser mics have in common is their flat response in the lows and mids, combined with mild to moderate boosts in the upper mids and highs where cymbals have a lot of complex overtones. These objective characteristics translate into the subjective descriptions such as “openness” or “air” that one generally hears about classic condensers. Of course, it’s not practical or possible for many musicians to setup drum kits to play or record. Libraries of high-quality drum loops can be used to add natural-sounding drum tracks to songs.
The same presence that makes snares snappy also makes SM57s a top choice for micing guitar amps, because it helps rock guitar cut through the mix. Acoustic guitars, meanwhile, are more like cymbals in that it’s crucial to capture the details of high fequency overtones, so condenser mics are favored. In fact, in studios condensers are typically used to record all stringed instruments (banjo, mandolin, violin, cello, etc.), and most other instruments too (reeds, brass, etc.).
In most musical styles condensers are also used for vocals, because even though voice has less prominent high-frequency overtones than acoustic guitar, the detail and transparency of a condenser helps keep the singer’s connection to the listener intimate and direct. Ribbon mics are also a popular alternative for vocals, particularly when the overall character is intended to be smooth and rich.
Checking One, Two, Three
In track-by-track home recording, drums and keyboards are often MIDI-driven (sampled or synthetic), and electric guitars often go straight into the audio interface. So for most people, vocals are the most important instrument to consider in buying a mic, followed (depending on your musical style) by acoustic guitar. The good news is that the large-capsule condensers generally used for vocals also sound good for acoustic guitar, so if you sing and play in separate passes, a single good condenser mic may be all you need.
The first step is to narrow the possibilities down to a list of a few affordable mics that have a reputation not only for good sound but also for reliability. Ideally you know someone who works in a studio or pro audio store, who has had direct experience with affordable condensers, and whose judgement you trust. If not, there are lots of sites and forums on the Web offering opinions about which of these mics are great and which to avoid. Of course, these opinions are often contradictory, so take the time to find the mics that are praised most consistently by people who seem to know what they are talking about.
Once you’ve got a list of a half-dozen or so right-priced options, the second step is to try to validate subjective opinions with objective data. Start by going to Microphone Data and do an “advanced search” to get a list of condenser mics suitable for vocal use (over 1000). Checkboxes on the right allow you to compare any two mics side by side. As a reference, check the box for a classic large-diaphragm condenser that most everyone agrees is great for voice and instruments, such as a Neumann U87. Then, check the box for the first mic on your own list of mics and click Compare. On the resulting page, check how closely the cardioid freqency curve for your inexpensive mic matches that of your reference mic. Make a note, and repeat for each mic on your list.
The last step is to try out the mic before you buy. If that’s not possible, at least be sure you can take it back if you don’t like it, and carefully save all packaging when you open it up. Hopefully, that won’t be necessary. Having done your best to make an informed decision, you’ll likely find that your new mic is just what you need to bring the quality of your home recordings up to the next level.