Monday, December 28, 2009

Four Stereo Mic Arrays Compared - Take the blind test

View Array Comparison QuickTime Movie
AAC 320kbps Soundtrack [10 mb]
Adjust sound to comfortable playback level.

Alternate formats: sound-only .flac [download] ; sound-only [.mp3]

This test was conducted at the May 2009 "Recordist Campout," with the goal of comparing the localization (position) and depth (consistent distance) performance of stereo mic arrays. It features "pink noise" played with a boom box in 15 positions at a constant distance of 100 feet in an open, natural landscape. Although several arrays were tested, at the time of this writing, there are four to compare:

Rich Peet's "Cube Mic" with 4- Audio Technica AT-3202 Mics flush-mounted in four sides of high density foam cube shape. Designed for surround, two of the mics were used for this stereo test. They are angled 90 degrees and separated 14".

David Michael's Sennheiser MKH-40/30 M-S Pair. The MKH-30 is a figure 8 mic and the MKH-40 has a cardioid polar pattern. Care was taken to make sure the M-S decoding was optimized in post.

Gordon Hemptom's "Fritz" or Neumann KU81i binaural head mic with customized ears.

Rob Danielson's "Perp2Sphere" Mic with 2- Rode NT2000 mics in Omni mode with mic capsules facing-forward on opposite sides  8" diameter wooden sphere.

All of the recorders were "rolling" at once so sound stimuli in all of the tests are identical. The landscape is sloped at angle of about 10 degrees from left to right so other changes in apparent elevation can be attributed to differences in the mics/arrays. Here is another, slower-paced version of the test made with longer durations of the same clips.

At first, the pans can seem quite similar, but by playing the test a number of times at a comfortable sound level, significant differences can emerge. Using processes of elimination and what they already know about mic array traits, the field recordists I have shared the test with have been able to identify arrays used with a high degree of accuracy. They have pointed-out differences in horizontal spacing as well as depth (apparent distance from the mic across the stereo field) and overall consistency or smoothness. Several have commented that it helps to close your eyes and visualize a boom box playing short excerpts of pink noise across a 200' wide landscape. The different mics used in the arrays account for much of the frequency response differences heard. After you have noted the performance differences and allocated them to appropriate array types, here's a chart identifying the mic arrays to see how you fared.

Visitors are welcome to leave observations and questions about the test below. Rob D.


At 3:10 AM, Blogger gabriele said...

Hi Rob,

my name is Gabriele. I'd like to make some questions about the Rich Peet's AT3032s foam cube.

I listened to the test and I liked the stereo passage of the noise from left to right.

Does the foam act like a sort of barrier between the At3032s angled 90deg or is it like having 4 spaced omnis?

Are there any phase issues in a mixdown to mono?

How else could I set up 4 AT3032s to make a surround array?

Thank you very much.

Gabriele Fasano

At 4:18 AM, Blogger Rob D. said...

Hi Gabriele-

There appears to be some boundary effect created by the foam but not as pronounced as a hard surface boundary would be. I'm not aware of any phase issues.

The amplitude of sounds in the center or between the mics with the Cube is lower compared to other array designs.

There are many ways to make surround arrays with 3032s. The DIY Boundary Mics Blog has some stereo arrays that are being used for surround and stereo. There are several theories for surround imagery with differing strengths and weaknesses. Many personal preferences and other factors involved in what folks like best.

I'm currently using spaced stereo pairs with medium-sized SASS-like DIY arrays and/or Jecklin Discs. Here is one spaced pair example,

Rob D.

At 9:00 AM, Blogger gabriele said...

Hi Rob,

Thanks for your reply!

Please could you tell me how does the Rich's foam cube sounds?
Are there any 'holes' in the surround image?

I built an AT3032s wooden stereo set up as shown on Curt Olson's blog and I'm very happy with the results. Do you think I could make a surround rig composed by 2 wooden set up like that, opposed to each other and separated 14'' or more like in the Rich's foam cube?

Thank you very much again for your help!


At 10:09 AM, Blogger Rob D. said...

Hi Gabriele-
I personally prefer what I can do with spaced stereo pairs over a symmetrical array. Human hearing is not at all symmetrical. As I said, the "centers" between the mics on the Cube have lower gain. There is no perfect mic array-- thre are strengthsand weaknesses and the speaker systems and setting for surround playback have huge influences on results too.

The neat thing about the DIY boundary arrays, besides the interesting spatial qualities they are capable of, is they are easy and inexpensive to make. You can make several types and try them all. This will teach you a lot more than people's suggestions.

There's a small email list of nature recordists who work in surround that I can direct you. Its best that you build some of the arrays and become familiar with some of the differences in performance you hear. The DIY Boundary Mics Blog has many of the designs. Rob D.


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