Greetings All,
I'm glad the topic of Blumlein, ORTF, etc. came up. I've been doing a lot of
music recording (in contrast to my usual cochlear implant research). Included
in my arsenal is an SSL console, Neumann U149 mics, an AEA R44 ribbon mic (plus
several Royer ribbon ics), superb musicians, and more.
Because of a recent article ("The Science and Art of Ambisonics") that appeared
in the April 2012 issue of Recording magazine, I have received questions from
students regarding my TetraMic and the Harpex software downloads (free player
and trial version of their VST). I use the VST (along with Nuendo) because it
provides the HRTF conversions. The HRTF reference that best matches my head
seems to be number 1051.
The Blumlein and ORTF settings give very different results when playing back a
walk-around-the-mic dialog. To make the sample recording, my girlfiriend
(Janice) and I read from a script and we rotated positions while the other was
reading. To be clearer: We initially mapped out eight positions (0, 45, 90,
135, 180, 225, 270, and 315 degrees) with 0 being straight ahead. The rotation
was counterclockwise, and a TetraMic was used along with a TASCAM DR-680. An
Earthworks measurement mic was also used to measure levels (a cal file was
created using an acoustical calibrator). The A-format files were converted to
B-format using VVMic and the IIR files supplied with my TetraMic.
Next I used the Harpex VST (in Steinberg's Nuendo DAW) to create stereo and
binaural files. One file was created using the stereo/Blumlein setting, another
was stereo/ORTF, and a third was binaural/1051 ("1051" works best for my head).
The walk-around gives quite different spatial impressions using the difference
mic simulations. You can download the files (dummied down to mp3) and see
photos of my mic arrays by going to cochlearconcepts.com/music_page/
(Note: I don't have a link from the cochlearconcept front page, so you have to
manually enter www.cochlearconcepts.com/music_page/ in your browser.)
With the Blumlein setting and listening under headphones, voices that
originated from the back left appear to come from the right. Similarly, voices
from the back right appear to the left. For sounds originating from the front,
everything is natural and isn't too different sounding from the HRTF setting.
But in a "surround" of sound (to include naturally-occuring reverberation),
sounds from the rear are "off" (laterally crossed).
The ORTF gives what one might expect: Strong signals, left and right, for
sounds originating from the front L and R, respectively, while sounds from
behind are mostly rejected. Placement of sounds is correct (through headphones
it's more lateralization than localization, but no contralateral errors)
despite levels being weaker for rearward sounds. I'm actually a proponent of
ORTF for music recording, especially when isolating other musicians playing
simultaneously in a session.
The HRTF setting works quite nicely. The sense of placement and level is what
we'd expect: Sound from the right rear appear to originate from this location
when listening under my Sennheiser HDA 200 headphones. AKG 214 phones work ok,
too, but not as well as the Sennheiser's. Note: All of the files come from the
same B-format file. L-R errors aren't because the B-format files were in the
wrong order (W thru Z).
Anyway, listening to the surround recording of a live source might shed light
on what the software is doing. I welcome you to take a listen (link provided
above).
For those who may be curious, the photos on the same link are briefly described
below:
a_001: Janice and my array of mics while video taping a live music performance.
The group being recorded, Turning Point, used to open for the popular
jazz-fusion band SpyroGyra in L.V. I haven't processed all the files (yet).
a_002: TetraMic setup for making recordings that I uploaded (ORTF, HRTF,
Blumlein)
a_003: Neumann U149 tube condenser mic and sax
a_004: Another Neuman U149 being used to mic upright bass
a_005: AEA R44 awaiting yours truly for some truly awful vocals
a_006: Pair of vintage Neumann KM 84s for drum overheads (mics in X-Y
configuration)
a_007: Student seated at an SSL 4000E/G console (console previoiusly belonged
to Turner Broadcasting)
b_001: Turning Point (jazz band)
b_001: AKG mics in "mini" ORTF config to close-mic a piano (lid almost closed
in order to isolate piano)
Happy listening,
Eric
Eric L. Carmichel
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