Thursday, April 05, 2007

Which has more depth, omni or cardioid?

Brian Farrel wrote:
"HI Rob, I would like to ask you, if you don't mind too much, to help me understand the logic in choosing an omni for upon the set up I'm [planning]. "

For your "Up" mic to be played back on a speaker above the audience in your lecture room surround system, I'd go with the omni because I think the omni mic can produce more depth of the sort this channel might profit from. Here's a a QuickTime movie test I did with the NT2000 parallel boundary rig comparing stereo imaging/localization/depth with the same mics. First are the mics in omni pattern and then in cardioid. The clock ticks pan from left to right in six positions from 9 o'clock, to 10, to 11, to 12, to 1, to 2 and to 3 o'clock.

The localization seems to be stronger with the cardioid polar pattern, but I think the cardioid's tonal balance is more "tuby" (resonant in the low mids) making the ticks with the cardioid polar patterns seem too close. I believe I can also can imagine the distance of the clocks from the mics more accurately with the omni patterns-- for both the closer clock I'm moving and the stationary one in the distance.

Its a subtle difference and harder to hear because the sound bits have a lot of distractions. Rob D.

1 comment:

Curt Olson said...

I agree with you, Rob, both from your quick test here and from my own extensive listening tests. Cardioids can deliver superior L-R localization if arranged properly, but I feel they tend to significantly "flatten" the depth of field. To my ear, omnis can render a much more vibrant sense of space and distance to the sound source. And, if arranged properly, localizaton does not necessarily have to suffer too much.

Each has a useful place, with each presenting its own set of trade-offs and compromises in terms of desireable and undesireable qualities. The choice swings on exactly what the recordist hopes to accomplish with any specific recording.