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Gear / Technical Help => Microphones & Setup => Topic started by: dabbler on August 02, 2015, 08:29:46 AM

Title: Is this ORTF or X-Y?
Post by: dabbler on August 02, 2015, 08:29:46 AM

I've been aiming for X-Y, but the distance at '?' widens to 1-2 inches in practice.

(drawings not to scale)


    PA/stage


    _  ?  _   elements around 100 degrees apart
   //     \\
  //       \\
 //         \\
  |         |
  |         | cable


So I'm not sure if my recordings should be documented as X-Y or ORTF, as I'm under the impression ORTF spacing is the other way around, like this:


     PA/stage


      _   _   elements around 100 degrees apart
      \\ //
       \v/
       /^\
      // \\
     //   \\
      |   |   cable


This is only for the purposes of documentation.  I've always been ending up doing what's in the top picture.

Or I can just include the ASCII art with every .txt file I release :)

Title: Re: Is this ORTF or X-Y?
Post by: Life In Rewind on August 02, 2015, 08:33:16 AM

This should answer you quesitons:

http://www.dpamicrophones.com/en/Mic-University/Stereo-Techniques.aspx

Title: Re: Is this ORTF or X-Y?
Post by: dabbler on August 02, 2015, 09:04:44 AM

Actually, reading DPA's microphone university is what got me thinking whether I was documenting correctly, since none of the pictures match up to what I'm doing.

"Slightly Spaced X-Y" ?

Or just: "Super Secret 007 Stealth Ninja Technique" >:D

Title: Re: Is this ORTF or X-Y?
Post by: Bruce Watson on August 02, 2015, 11:30:33 AM

Quote from: dabbler on August 02, 2015, 09:04:44 AM

"Slightly Spaced X-Y" ?

Correct. ORTF is (off the top of my head, so someone please correct me if I'm wrong) defined to be 17cm spacing between capsules, and capsules angled 110 degrees apart, and cardioid mics. This gives you a stereo image that comes from both time delay and from loudness differences. XY on the other hand has the capsules aligned (coincident), typically in an "over under" configuration. It gives you a stereo image that is all loudness differences, with no time delay (phasing) differences. And again, using cardioid mics.

Title: Re: Is this ORTF or X-Y?
Post by: Gutbucket on August 03, 2015, 04:57:57 PM

If you can, it's much better to set up like the second ASCII art diagram above, with the leftward pointing microphone positioned to the left of the rightward pointing one.  If set up like the top diagram, the time-difference and signal-level stereo que's contradict each other.

As for documentation, it's best to specify the actual spacing and angle between microphones and the microphone pickup pattern, which avoids confusion.

example: cardioids, spaced 2 inches / 100 degrees

But that assumes the microphones are spaced towards their correct sides, as explained above. With them 'backwards' (leftward pointing microphone positioned to the right of the rightward pointing one), it would be best to specifically note that, or include the ASCII diagram.

One thing for sure is that neither are ORTF, which is more specific than any other configuration @ 17 cm / 110 degrees, specifically using small diaphragm cardioids.  If using different spacings, angles, patterns or microphone types it's not ORTF.

Edit- somewhat similarly, there can be no such thing as "slightly-spaced X/Y", because the assumption is that any X/Y setup has two microphones positioned so that they are fully coincident with no horizontal spacing at all between them.  Angle between capsules and pickup pattern can vary, but not the coincident spacing arrangement with no horizontal spacing.