Topic: NOS / ORTF pattern question

[lsd2525]

Going to be open-taping at the local Fillmore tomorrow with my AT853's. I did an outside gig last week and ran X-Y and didn't really like the sound. Anyways, my question is: If I run mics at 90 degrees and they are pointing to the outside of the stacks, should I be concerned? Or should I narrow it down to say 60-70 degrees and aim straight at the stacks? I imagine the stereo image would't be a great, but something about the mics pointing outside of the stacks scares me. Am I crazy? Any suggestions would be welcome.

[yltfan]

Where will you be in relation to the stage/speakers?

[lsd2525]

Hopefully around the soundboard, guessing 50 feet back or so

[lsd2525]

Check out the 2nd photo, taken from right behind the board

https://www.google.com/maps/preview/uv?hl=en&pb=!1s0x8856a037b0cd7c1f:0xa561448b68aa901d!2m5!2m2!1i80!2i80!3m1!2i100!3m1!7e1!4shttps://plus.google.com/108996689952831750999/photos?hl%3Den%26socfid%3Dweb:lu:kp:placepageimage%26socpid%3D1!5sfillmore+charlotte+-+Google+Search&sa=X&ei=R75MUqHgN8WMygHGhoGoBw&sqi=2&ved=0CJkBEKIqMAs

[DSatz]

I suggest that you try not to think so much about where your individual microphones are "pointing," which is a valid enough concept in mono recording. But stereo recording/playback is different. In stereo the two (or more) microphones act together to create (by way of the loudspeakers in playback) a combined stimulus for your ears and brain--which in turn act together in some ways that are quite different from the way they work when you're listening in mono.

This isn't some mystical bullshit. I'm trying to be as concrete and realistic as I can, while staying with the basics.

Something very important to realize: No matter what microphones you have, they don't have narrow pickup patterns. One good definition of a cardioid (the most commonly used microphone pattern by far) would be that it picks up sound arriving from nearly all angles, except for the back.

Acoustically speaking, a cardioid has 50% pressure response and 50% velocity response. The pressure component is omnidirectional. So even if you put two cardioids back to back (thus creating as much difference as you possibly can for a coincident pair of cardioids), at least 50% of the signal energy coming from the pair will still be identical in its content, phase and amplitude. (The "at least" part is because in any halfway normal listening or performing space, the sound sources themselves will have some correlation between the left and right sides.) Set the mikes up with any angle less than 180 degrees between them and the percentage of shared, identical signal energy will only increase from that 50% minimum. Setting a pair of coincident cardioids with their axes only 90 degrees apart, for example, at typical recording distances, means that the resulting recording will be damn near monophonic--the difference between the two channels (the stereo information) will be only some fraction of the amplitude of the common (mono) signal.

So try to think more as if you are putting up a single stereo microphone with a certain set of stereo pickup characteristics (even if you see two pointy components sticking out from it at some angle or other), and try to choose the optimal characteristics for that stereo microphone, and to place it in the best place you can. I think you will make better, more interesting-sounding recordings if you look at things that way. Let your ears inform your eyes.

--best regards

[lsd2525]

Thanks Dsatz. That is an interesting way to look at it. So something like a 120 degree angle will yield a more "stereo sound" than a 90 degree.

[page]

So something like a 120 degree angle will yield a more "stereo sound" than a 90 degree.

in short, yes.

that is a generic statement and it doesn't take into account how much information is duplicated between channels (which impacts our perception of "stereo") nor does it take into account any other factors that impact "stereoness"

[ScoobieKW]

There is a highly useful concept commonly called Stereo Zoom. (well, ok. commonly called within  a small section of people who know about it)

Basically it shows how by changing the distance between the mics and the angle between them you can change the perceived stereo picture.

Michael Williams has written several papers about it, this is a good starting point.

http://www.rycote.com/images/uploads/The_Stereophonic_Zoom.pdf

Neumann makes a smartphone app that show you how changing these variables changes the recording angle.

This web application is also useful for understanding Stereo Zoom

http://www.sengpielaudio.com/Visualization-ORTF-E.htm

There are presets for common configs like ORTF and XY, you can also drag the mics by the circles on the green lines. this lets you change angle and distance.