Saturday, October 08, 2011

Olson "Wing" Array Comparison with Danielson PBMB2

Download Blind Comparison Movie [13 mb .ZIP] -Use QuickTime 7 Player with Progress Bar 
[Movie has 256Kbs ACC* soundtrack. Uncompressed soundtrack is here: .AIFF 105 mb]

The black rig at the bottom of the photo is Curt Olson's "Wing" array constructed from a 8.5" length of 2X6 standard lumber (1.5" X ~5.5") with 1.5" wide wings. AT3032 mics are setback 1-7/8" from the front edges. The array was titled downward about 20 degrees. At the top of the photo is Rob Danielson's PBMB2 array larger SASS-like array; specs are available here. The PBMB2 is wrapped with fiberglass furnace filter media.

Olson's array was recorded with 59.8 dB of gain on a SD 744T and Danielson's used a 60 B of gain on Symmetrix SX-202 Mic Preamp into a Focusrite Saffire Pro 24 audio interface. Both arrays used AT3032 mics. The flush-to-boundary mounting of the mics in the PBMB2 array seemed to contribute more gain than the double perpendicular-to-boundaries arrangement of the "wing" array, but the exact amount could not be determined.  

The systems recorded simultaneously through one night at a rural location in Southwest Wisconsin and includes Barred owls, an Eastern Screech Owl, a Coyote and a Dawn Cardinal on October 6-7, 2011. Other surround recordings from this location may be found here.

*Note: The ACC compression in the movie soundtrack affected the tonal balance of the recordings-- particularly the impact of the insects.  Download the original .aiff  for a more accurate  evaluation. Equalization and stereo image adjustments were based on speaker monitoring in a setting with minimal background interference.

Comments and observations are welcome below or on the Boundary Mic List (subscribe)

1 comment:

Rob D. said...

[Note: the below if from my response to the email list associated with this blog.]

Hi Vicki, Mike, Hector et al--
Yes, same mic types were used.

Your guesses are all correct. A is the Wing Array.

Its interesting to read your headphone evaluations. Width can be adjusted in post, of course. There's is more center presence with the wing array both volume and with higher frequencies. These can be adjusted with EQ inserted into M-S processing. A sense of "width" can be also emphasized with phase difference in the bass and the PBB2 has a bit more of this it seems.

I attempted to address width too in the EQ'd section but only while referencing the coyote segments. The other segments inherent this EQ.

My theory about the localization difference is the greater Hz response of the PBMB2 from 400-1600 Hz. I feel these emphasis provides more spatial cue subtleties for lower Hz sounds like the owls and the "tails" of sounds as they reflect and their tone becomes "darker." For example, the attack (higher Hz) edge of the coyote bark localizes much better with the Wing array but the body of the howls seems to localize better with the larger boundary array. I still hear a lot of shifting or confusion in apparent position over speakers with both arrays for these distant events.

That said, the test could be a good example of how one array can't do both and how "flat" response may not be the best approach in designing an array for this kind of recording. That people are agreeing is useful.

Its crucial, of course, that most of the samples address sounds coming from a great distance. Notice how different the cardinal and finch localize at the end!? Not a coincidence. I emphasized localization at a distance when testing/altering the SASS design. Boosting response circa 1400 Hz is not very consistent with most theory which suggests the array needs to improve HZ response for distant subjects.

I went back and forth between the two recordings when EQ/imaging trying to shoot for the same "ideal" as much as I could. I only did the EQ once, though. It usually requires several separate attempts to get a result I'm content with.

The Hz response of the two arrays is very different; they present different "starting" gestalts. Heard in comparison, there are some edgy qualities in the additional bite of the Wing array that I only modestly addressed. I could have used wide EQ bands to more closely match the tonal balance of the insect sounds in the two arrays but it would have made the Wing sound too life-less. I used thin notches. There is excessive resonance under 700Hz in the PBMB2 that is not in the Wing array. Both arrays have about the same amount of low mid-range "grunge" from exaggerated tones in the 125-700Hz range. I used different pitches to address it with each array but the total amount needed addressing was about the same. The PBMB2's response from 700 Hz to ~1900 Hz required less messing with. Normally I would add some more "air" to the PBMB2 around 1900-2800 Hz but with the insects so prominent, I didn't for these recording samples.

I suspect the insect sounds might be most affected by the double boundary design. Looking at scale of the the Wing array's boundaries and angles, I'm guessing that sound waves under 2000 Hz aren't affected nearly as much as those above 5KHz.

The front and rear imaging on both arrays is more comparable than I would have guessed. Tilting the wing array forward may block off more direct sound from the rear and produce less confusion. The off-axis Hz drop off for both arrays is more similar than I would have guessed. Maybe the greater directionality of the larger boundaries boosts enough gain starting around 2 o'clock to offset the greater warmth to the far sides the PBMB2 has.