I’ve been getting requests recently for broadcast mixing consoles that can handle 4, 6, or even 10 or more microphones. It appears that lively group discussions are popular right now. Whether the topic is sports, politics, or general gossip… people want to have a loosely-structured chat session where anyone can jump in at any time with their opinion.

This isn’t the usual, “everybody wears headphones, everybody sits in front of a boom mic” situation. It’s more like a bunch of folks sitting around a table or on a couch and chatting. Think of a party in your living room, or a bunch of friends at a bar. Most people don’t wear headphones to hear each other in your living room.

This type of scenario can be difficult to mix. The reality is that most stations don’t have the staff to engineer for a group like this, so the equipment has to take care of itself. What’s the best way to manage a large number of mics for a broadcast?

First, determine the best approach to hearing all the participants. If they are all sitting around a conference table, a mic in front of every person (or one between every other person) is best. Choose mics with a cardioid pickup pattern, to maximize pickup of the person in front of the mic, while reducing pickup of voices off to the side.

If the group is not at a table, try using boundary mics. This type of mic hears much the same way as our ears do. When a person several feet away from you speaks, you are not aware of any “room echo”. The boundary mic will pick up the sound in the same way… with hardly any “room echo.” Conventional mics tend to collect a lot of undesirable room noise.

Boundary mics can be positioned on tabletops, or on the walls near the action. If you haven’t tried one of these before, you will be impressed with their behavior. Place several mics around the participants. More is better.

It won’t do to simply turn up all the mics and hope for the best. You’ll collect an overwhelming amount of noise, and the person speaking will be difficult to hear. Each mic needs to be controlled so it is active only when someone is speaking near it. Each mic’s signal should pass through a downward expander to effectively turn it down when no one is speaking in its vicinity, and a compressor to keep the speech level reasonably constant. (A downward expander has a more subtle behavior than a “gate”. A gate is more abrupt in its on/off action, and calls attention to itself.)

Some high-end live sound mixers have expanders and compressors built in to each mic channel. However, most broadcast applications will use a separate mic processor for each mic. A good cost-effective choice is the dbx 286A. It provides the mic preamp, expander, and compressor. For a large number of channels in a single device, check the Jupiter series of DSP engines from Symetrix, available in 4, 8, and 12 channel versions.

The person engineering the show (most likely the on-air talent) will wear a headphone, to confirm that everyone is being heard properly. The other participants won’t need them unless they need to interact with external audio, like a telephone call. But that’s another topic for another column…

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