I'm sure you've heard the terms Mono and Stereo over the course of your podcast setup. Have you ever wondered what they really mean? Think of the two terms as adjectives - descriptive terms for the 'direction' that an audio signal is presented to the listener.
Mono, which is actually an abbreviation for the term "monaural" or "monophonic" literally means one channel of sound, coming from one direction. Think of old-time radio or AM radio in the car (remember AM radio?). Certain audio such as music when presented in mono sounds dull and flat with no ambient characteristic. It's like listening to a single small speaker on your television or cell phone. However, other audio such as the human voice when presented in mono sounds natural. This is because our vocal cords can only produce a monaural signal. This is why we always recommend recording voice in mono.
Stereo, which is short for "stereophonic" introduces an audio image as two channels of sound, coming from different directions. And the way that our heads, ears and brain works, it allows us to actually perceive what we call left, center, and right. In a stereo recording, there is an electrical phase relationship between the 2 channels (left and right) and are recorded together. So audio content such as music, if recorded in stereo, presents an ambient stage where we can now hear it come alive in an almost 3D sense. We can follow a guitar sound from the left side to the center to the right side. The stereo effect is most pronounced when wearing earphones and listening to our favorite music. However, on the flip side, audio content that is mono in nature such as the human voice, when recorded in stereo leads to issues of quality where instead of just recording the voice in it's natural mono state you are now recording the room ambiance along with it, bringing echo and slap-back into the recording because it's now recording 2 channels instead of 1. This is another reason to not use "stereo" microphones for recording voice.
Now when it comes to podcast recording of interviews, mono and stereo actually have a couple of different meanings. Because now instead of describing the 'direction' of the sound, we now use these terms to define the number of recorded channels for each person speaking. At the end of the day, your eventual podcast episode will be mixed down into either 1 (mono) or 2 (stereo) channels even though you might have recorded 3 or 4 for the show. This is because 99.9% of the way your audience will be listening to your show is either via their Ipod, car stereo, or the internet - and those only come in 2 channel stereo.
So when recording your guest interview, it is always suggested that each party is recorded on their own separate channels, in mono. For instance you, the interviewer would only be on the left channel and your interviewee would only be on the right channel. Pamela for Skype, for example offers this function. However, and this is where it gets complicated - when you record in this fashion you are now recording a "stereo" file (stereo here meaning 2 channels) but it contains 2 "mono" channels (you + interviewee). The computer will call it stereo, but it's really 2 channel mono. It isn't stereo because that electronic relationship I was talking about earlier doesn't exist because the channels were recorded separate from each other.
The main benefit to recording your interviews with each person on their own channel is to allow the editor to remove unwanted sounds or words from each person individually without affecting the other person's audio. For instance, let's say you are using Skype and you are asking your interviewee a question and they sneeze really loudly twice in the middle of your question. Since your audio is on it's own channel and your guest's is on their own channel, the audio editor can remove just the sneezes without affecting your question, and the audience would never be the wiser.
If you and your co-host are in the same physical room, and sitting very close to each other, yet each of you have your own microphone, and you are recording on separate channels, depending on how loudly you talk, your voice will be picked up by the other person's microphone. If your co-host sneezes, it will be recorded on your microphone too, albeit at different volumes. This time, the editor won't be able to remove the sneeze 100%.
In the end, there are many different ways to record your show's audio. But fundamentally the most important is that you record voice in mono, and at the same time, try to keep all people on their own channels of audio whenever possible. Please contact me at anytime if you should have any questions on your own audio setup and I would be happy to make recommendations and suggestions for making it sound it's very best.