There are many online resources available that can tell you all about the nuances of microphones, and I’m not going to try to reproduce them here. Instead, I want to give you a quick primer on a few different types of microphones and what they can be used for.
These do pretty much what they say they do: record sound from all directions. They will pick up more from the front than the back, but they give you a good dose of all of the sound in the area.
Omnidirectional mics are great for getting the feel for a place. They will record ambient sounds without emphasizing any of them too much (besides the fact that physics dictates that nearby sounds will be way louder than far away sounds). In an interview, an omni mic will give a sense that you are in a location, but can pick up background sounds in a distracting way if you aren’t careful. Put one close enough to the subject and you’ll get a good mix of foreground and background sound — provided that the setting isn’t too loud.
These are more directional than omni mics and are sometimes called unidirectional microphones. They come in different “amounts of directionality,” from slightly directional to very directional. They also pick up very well from the back of the mic — where the handle of a handheld mic usually is. This means that some cardioid mics are very susceptible to handling noise and vibration.
Using a cardioid mic gives you that “radio sound” you are used to from DJs and talk radio hosts. This is because of something called the Proximity Effect that enhances the bass in a voice when the microphone is very close to the speaker’s mouth (close as in a few inches away). The main reason for using a cardioid mic in a podcast is to reduce the background environmental noise. A directional mic will not eliminate background noise, but it will make it less distracting.
These can also be called shotgun microphones, depending upon their characteristics and shape. Hypercardiod microphones pick up sound from a very specific area in front of the mic, and can share handling-noise issues with their less-directional cardiod siblings.
These mics are not magical, so don’t expect to use one to record a speaker 20 feet away and get amazing sound. For interviews and other spoken-word recordings, you should treat these microphones just like the others. They will allow you to record in situations that would be hard with other mics, and they can give you a studio-like sound in the field, but they don’t work miracles.
Stereo vs. Mono
The difference here should be pretty obvious: In stereo, the left and right speakers produce different sounds, and in mono they produce the same sound. When it comes to microphones, you need two to record stereo and one to record mono. Of course, there are many microphones that include two recording elements in one casing, so stereo doesn’t always mean two wires running to two devices.
Unless you are podcasting music, stereo isn’t a necessity for most shows. In fact, getting really close to a stereo mic can cause some very weird issues with your sound. However, an exception to the “stereo is unnecessary” rule can be seen in my Hat Mics post, where I use a pair of stereo mics to record two separate tracks into one file.
There are many types of microphones designed for very specific tasks. I won’t go into the details of all of them but here are a couple of types that could be of interest to podcasters:
XY Stereo Microphones: For recording a more directional, authentic-sounding stereo sound. These are some of the only stereo mics that can easily be used for voice recording like a mono mic without sounding strange. (See the built-in mics of the Zoom H4 for an example of an XY setup.)
In- Ear Binaural Microphones: Because they sit in your ears, mics like these from Sound Professionals give a 3D feel by recording exactly what you hear. The catch is that they only give that 3D feel through headphones, otherwise they are just stereo mics. You can hear a recording I made with this type of microphone below.