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I'd like to record some round-table type discussions for a podcasting project I have in mind, but although I've done some recording of music I don't really know how to start with this.

Should I be looking at omni-directional microphones or several directional ones? If possible I would like to avoid having a microphone per participant just because that could need a fair few mics more than I have. Having people interacting in the same space, I would guess that levels of bleed are likely to affect the ability to change things too significantly even if I can mic everyone up?

I'd be particularly interested to know how radio shows that use discussions or radio dramas work around having multiple participants in the same room.

Following on from @ntt's comment, I would expect to be working indoors, in a room of our choosing ( but along the lines of chosen from a few people's houses rather than chosen from a selection of high quality studios ) so advice on the best type of space to use for this is also helpful. I was assuming that somewhere reasonably sonically dead without too much in the way of echoes, boomy flooring and so on.

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Would be interesting to know the kind of environment you're recording in.. Is it in a room or outside? Will it be noisy? –  notthetup Feb 22 '11 at 11:33
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3 Answers

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Unfortunately, the choice of microphone and positioning is going to be dependent on the acoustics of the room that the recording is being used in. If it's a fairly quiet room, then an omni mic would do a pretty good job. However, if there is noticeable air handling noise or other background noise, the microphone(s) will need to be closer to the people talking. As the mics move close to the talkers, more mics will be needed to get appropriate coverage. In poor rooms, it is necessary to have a gooseneck mic per talker in order to get the mic close enough to the talker.

Also, when using multiple mics like this, you'll want to use an automatic mixer. Think of this: If you have 8 open directional mics, you'll end up picking up so much ambient noise, that the sound quality will be similar to using a single omni mic. Thus, an auto mixer is essential to keep the unused microphones gated off.

Your application is extremely similar to teleconferencing, so any advice that you see for teleconferencing would also apply to you.

See the following links:

Acoustics of Teleconference Rooms

Audio Systems Guide to Meeting Facilities

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This is really useful, thank you. –  glenatron Mar 11 '11 at 10:10
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Since each participant is not isolated, you may as well go for an omni directional mic. Monitor the levels before hand to make sure you can hear everyone clearly.

If you have to, you can always tweak it in post.

The other alternative is a bunch of semi-cheap headsets (headphone

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When you're at a table, a boundry effect microphone is a nice way to go -- provided you don't have anyone thumping for emphasis.

I like my Crown PZM-30D. I often use it at Church. In that case, I'm doing live sound reinforcement, while at the same time, I've got a second mix for remote rooms and recording to mp3 and DVD. I keep a PZM-30D stuck to the inside of the lid on the open grand piano. I only run the PZM into the record mix. So, the piano goes onto the mix at normal levels, and, if there is some Q&A or someone stands to speak and I can't get a wireless handheld to them in time, I just crank up the PZM and it picks them up fine with just a little bit of reverb off of the tall walls.

Edit:

To answer your sub-question: Recording studios use large diaphragm cardioid mics. You can see them in use if you watch the DVD extras on any animated movie. The actors are about four inches from the mic. Not eating the mic, but still very much in your face. The gain is cranked way up, but they're in a dead room. If they have more than one actor in the studio, they're separated by five or six feet to avoid crosstalk. Their goal is high fidelity.

Important factors to consider: How unobtrusive do you want to be? A big mic and stand in front of each person will get in their way. They'll want to make eye contact with the other participants.

How much will they move around? If they don't talk into the mounted mic, then you're going to have parts of the conversation fade out unless you are there making moment by moment adjustments to the gains. And, your mixer had better have auto-ducking to keep the background noise from all the open mics from drowning out the person talking.

How big is your table and recording space? Individual mics, unless they are lapel-worn, are going to take up a lot of room, and you're going to be pushing everyone further away from each other to avoid cross-talk interference. (Auto-ducking would also help avoid the interference.)

How often are you doing this? Setting up and packing up more mics takes more time. You have more points of failure to check -- cables, connections, knobs, switches.

On the other hand, you can have an intimate conversation around a round or roughly square table with a single hemispherical BZM in the middle. Setup time is short. The BZM actually rejects noise transmitted by the surface it is on very well. If your participants are equidistant, gain issues are nonexistent.

A single BZM mic handled a 9-person teleconference table on a system I helped to engineer 30 years ago. There were millions of dollars of PTZ cameras, switches, projectors, touchscreens, codecs, and satellite uplinks -- and then there was one BZM sitting on the table. All that video and computer gear would be useless if you couldn't hear the other end, but the BZM did the job.

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