Jeff,
Fo the best results, you really need to manually operate the boom (and input level) for more than one person. In fact, when I do location audio for single person interviews using a static boom, I frequently ride gain through the entire interview. A few folks have relatively constant speaking levels, but many begin hot and get soft as they continue to speak (and run out of air).
Once I figure out their patterns, I adjust. I know, for example, that I need to turn down slightly for the first few words and then slowly increase the gain. I can do this ONLY if the ambient noise is low enough not to be heard as I turn the mic up. The result is a much more finished track.
Attempting to mic three with one locked down boom is bound to cause problems because no two people speak at the same level. Yes, you can (should) fix that in post, but will you?
Regards,
Ty Ford
Cow Audio Forum Leader
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