There are a number of reasons to record sound isotropically, or equally from all directions: to capture the totality of environments and natural sound; to capture music organically as if from an “in the thick of it” perspective; and, last but not least, to capture sound that, when paired with video capture or animation (that is coincidentally from the same point in space), will recreate a virtual reality. With emphasis on the latter, Sennheiser’s Ambeo VR mic uses four pre-polarized KE14 condenser capsules in a tetrahedral array. When processed with Sennheiser’s own ambisonic software and third-party down-mix software, Ambeo VR’s signals can be decoded to stereo, surround sound or a fully spherical 360-degree soundfield, contained in four channels of B-format ambisonic audio as utilized in today’s interactive virtual reality (VR) standards.
Sennheiser’s Ambeo VR mic isn’t much bigger than a handheld condenser (at 215 mm), with only a slightly larger head basket to tip you off to the unusual contents hidden behind its three-stage windscreen. Here, these four cardioid capsules are utilized in an arrangement where none are pointing directly to the front or sides, but all are at 45 degrees off-axis. This arrangement allows for a sort of “Mid-Side-times-four” arrangement. The mic requires 4x phantom power (typical 48 V, but to all four capsules), will handle 130 dB(A) at 1 kHz, and has 18 dBA of self-noise.
Ambeo VR’s four capsules directly feed four outputs on a 12-pin DIN connection that terminates in a four XLR-M pigtail that is 18 inches long. The mic mounts via a Rycote suspension: one of those types with plastic suspension arms for cushioning (rather than elastic bands) and very tight tolerances to firmly grip the mic without any threading or tightening of nuts. A foam windscreen and only a foam cutout/cardboard storage box are provided in a no-frills, budget package at $1,695. The mic has a two-year warranty.
|Sennheiser’s Ambeo VR mic uses four pre-polarized KE14 condenser capsules in a tetrahedral array.
However, this microphone hardware would be for naught without some proper Ambisonic software. Sennheiser provides its Ambeo A-B Format Converter software (Mac OS X/Windows OS-ready) as a free download. This software will take the mic’s A-format, four-channel output and convert it to four-channel Ambisonic B-format audio. Within that software, users can rotate the sound field left or right (simulating the turning of your head), engage a global high-pass filter, apply Ambisonic filtering (said to enhance the imaging and soundstage when mixing for a 3-D sound field), place the software to the mic’s original positioning (either vertically up, which is the ideal method, straight down or horizontally), and mix to one of two Ambisonic formats (Classic FuMa or ambiX), all in post-production.
This B-format audio can be utilized by virtual reality content creators and monitored by users with HMD (head-mounted device) VR systems, where the user’s commands interactively steer and alter the audio playback. Conversely, using third-party software (which is plentiful), users can mix B-format audio into surround sound, 3-D binaural stereo or even mono. [For such binaural delivery, Sennhesier recommends Noisemaker’s AmbiHead plug-in, available at noisemakers.fr/ambihead/)—Ed.]
I have stereo monitoring in my recording studio and only work with surround sound at broadcast facilities, so my hands were somewhat tied when it came to the many apps capable with this mic. I have previously reviewed an Ambisonic mic and found it ideal for capturing immersive environments (useful for film, TV or NPR-style background “nats,” or natural sounds), live concert sound on-location, and even certain studio overdubs. But, without an “Ambisonic dome” of my own to allow for immersive surround-sound, I relied on binaural down mixes to test the Ambeo VR.
|Sennheiser’s Ambeo A-B Format Converter
I found preliminary tests with a trio of acoustic musicians, Foley and nats to be encouraging; the Ambeo was definitely isotropic and a lot more omnidirectional than any so-called “omnidirectional” mic I’ve ever used. The top end wasn’t excessively bright and there was strong bottom end, so any fears of a thin-sounding electret were put to rest. Dynamics seemed unrestrained and punchy with lots of headroom.
Seeking documentation, I set up the Ambeo in my slightly noisy control room about four feet from the floor in the vertical (and recommended) orientation. Sennheiser recommends four identical preamps—with exactly equal gain across all four—for proper imaging and stability. I used a Focusrite ISA428 mkII with 40 dB of gain and found a bit of a noise floor that I attributed to equipment fans and actual room noise, not the mic. I recorded all four channels to individual mono tracks, as well as a quad track. My DAW had numerous quad signal processors, but I didn’t use any in my mix in order to maintain signal purity. I did apply the Ambeo A-B Format Converter and found that the Ambisonic process took away a lot of raw bottom end that came off the mic, so I didn’t use the software’s high-pass filter. Likewise, with the ambisonic filter option, I bypassed it, too; it seemed to take away fullness and add some overbearing 12 kHz sizzle.
Next, I chose the ambiX output format and sent the signal to Noisemakers’ AmbiHead software for 3-D binaural processing. This software has powerful capabilities to steer the audio with Pitch, Yaw and Roll controls (chin up/down, swivel side-to-side, tilt left and right), stereo width, the ability to load numerous binaural head profiles and even add back some of that bass that seems to get lost in the Ambisonic process. AmbiHead worked ideally and translated the Ambeo’s information into a 360-degree experience that was actually discernible over headphones.
Hear my 90-second, stereo, 3-D binaural webclip that uses only voice, shaker and a couple of drums to illustrate a portion of the Ambeo’s abilities at prosoundnetwork.com/july2017. Also there is a web clip posted on YouTube via John Hendicott’s Aurelia Soundworks. The partially-interactive clip for NBC’s Blindspot uses the Ambeo VR for natural sound on set and then augments that with score, SFX and some close mics.
In use, I found microphone performance was excellent, but getting the mic in position was a little difficult. Perhaps I shouldn’t say “difficult,” as the mic itself is small enough, while the Rycote mount indeed holds firm. I was troubled with strain-relief. The Rycote suspension has a slim retaining clip to grab the four very small (yet strong) cables, but at only 18 inches long, there’s not enough length to get the connections down on the floor (where they belong). Instead, a bulky cluster of cables nearly overloaded the Rycote retaining clip with burden, and some velcro was needed to hold things in place without tension and without sag. A single 6-foot cable with a short fanout would be ideal and boom-pole-length cable extensions would be fantastic. (A 5-foot extension may now be shipping with the Ambeo mic, which I would highly recommend).
|Engineer John Hendicott of Aurelia Soundworks on location with Ambeo VR and the Rycote 25mm BBG kit.
For in-studio use, the mic’s head basket provided plenty of wind protection, but the supplied foam windscreen simply does not fit the mic—it’s too small. Instead, a wind zeppelin or perhaps a Rycote boom-pole/wind-kit would be ideal for location work. I’m told that the Rycote 25 mm BBG kit is perfect.
Simply stated, Sennheiser’s Ambeo VR is a very good condenser microphone with a well-balanced frequency response, powerful dynamics, ample sensitivity and nice stable imaging. Coupled with the Ambeo A-B Format Converter software and subsequent mixing and/or format conversion, its users have a phase coherent point-of-view that can be morphed into a useful perspective for surround sound or stereo applications, broadcast or music-based applications. Couple that B-format audio with game development, 3D movies, virtual reality HMDs and who-knows-what in the near future: Ambeo VR owners have a microphone that becomes a wildly creative tool on the cutting edge of post-modern content creation. Indeed, there are more expensive mic models as well as lower budget options in this burgeoning field. But Sennheiser’s Ambeo VR looks to be a very high-quality yet reasonably priced solution for futuristic immersive audio capture.