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.