It's very gratifying to read a thread such as this one. My hat (currently a bright blue "New York Liberty" cap) is off to the people who are in there experimenting and listening--even if to some extent, they're "re-inventing the wheel." The fact that some brave souls are making reasonable guesses and then trying those guesses out, listening to the results and refining their theories is wondrous to behold.
As opposed specifically to: people who start out with theories, love those theories above all else, and interpret whatever they see and hear so that their theories will seem to be upheld. I hereby declare myself a refugee from boards where that is the dominant attitude.
Still and all, let me try to make some people's work a little easier, perhaps.
#1: The omnis that most people are talking about here are small pressure transducers. Their behavior is quite different from the "omni" pattern of most multi-pattern microphones (the only exceptions, because of how they switch their patterns: Schoeps microphones and certain recent Shure KSMs). Some characteristics (e.g. the angles and spacings that work well for stereo recording) come from "omniness" in general, while other characteristics (e.g. extended low-frequency response; relative insensitivity to wind, handling noise or physical vibration) come from the fact that they're pressure transducers.
People who are running, for example, an LSD-2 or an AKG C 34 shouldn't expect the "omni" setting of their mikes to behave like the omnis discussed in this thread, since their kind of "omni" is synthesized from two back-to-back cardioids, and behaves more like a directional microphone in many respects. Also, at high frequencies their pattern is more bidirectional (or "propellor-shaped") and differs from that of a pressure microphone, which simply narrows its forward pattern at higher frequencies.
#2: Hooray for the people who tried it, listened, and found that a relatively small spacing between two omnis (just a few feet) is often enough for good stereo pickup--even when the sound source is quite wide. For some unfathomable reason, most of us Americans never seem to imagine that this approach is worth trying, let alone that it might actually work better (i.e. be less swimmy and phasey) than more widely-spaced omnis.
In Europe when people talk about "AB" stereo recording, they usually think of a moderately small distance between the mikes. The conventional American style (divide the overall width by three and place the microphones at the 1/3 and 2/3 positions--or even divide it by four and put the mikes at 1/4 and 3/4) seems very strange; can't we hear the "hole in the middle?" Sometimes I listen to the old Telarc orchestra recordings that won all those Grammy awards in the early days of the CD, and it helps me to understand why many people find a center microphone necessary as a rule (e.g. Decca Tree or the Nakamichi three-mike "curtain" approach). But sometimes a better solution comes about by not creating the defect in the first place.
#3: Someone pointed out that the closeness or distance of microphone placement seemed to affect the brightness or dullness of the pickup with omnis more than with other patterns. Again, hooray; what their ears were telling them was spot on. And as it turns out, this explains why there can never be any one type of omnidirectional microphone that is ideal for all types of setup and all styles of recording--any thought that one manufacturer or design approach has the supreme edge over all other brands and types is simply a misplaced notion (even more so with omnis than with any other kind of microphone, I would say).
The thing is, reflected sound and direct sound aren't just sound coming from one direction versus another. Reflected sound is sound with a past; it arrives later, it arrives over multiple paths (and thus at multiple angles of incidence and multiple arrival times), and it has bounced off of surfaces which have each taken a chunk out of the sound--usually at high frequencies most of all. So it is truly "diffuse," in three ways at once: incidence angles that approach randomness, arrival times that are spread out, and high-frequency content that's been dulled down.
For indoor recording, the farther away you get from the sound sources, the more reflected sound you'll pick up relative to the direct sound. At high frequencies, any but the tiniest (and therefore noisiest) of omnidirectional microphones are more sensitive to direct sound than diffuse sound, so you are immediately plunged into the midst of a balancing act. Since we all face practical constraints as to miking distances, angles, etc., different microphones are sometimes needed, or some corresponding equalization of the high frequencies in post.
This high-frequency absorption of reflected sound is generally desirable from the listener's point of view. It's certainly a part of what we hear in any concert venue, and if there isn't enough of it, the room sounds harsh and fatiguing. If anyone ever tries to sell you on a certain type of microphone because its elevated high-frequency response off axis "compensates" for these losses, perhaps that ought to set off one's BS detector--it's "fixing" something that wasn't broken in the first place. (Ordinarily it will be a directional microphone, though; as noted above, omnis have the exact opposite tendency.)
--OK, we suddenly have guests including a 4-year-old, so I'd better run. Thanks again for all the goodies in this thread. Yay you people.
--best regards
P.S. the next morning: Added a photo of a diffuse sound field as mimicked by the ginko leaves that fell last night.
Topic: Running Omnis??? (Read 14898 times)