Binaural Fun With AmbiExplorer For Android

AmbiExplorer_framedMy issue with use of the term 3D with reference to binaural voice conferencing service stems from the fact that I’ve been having some fun with real 3D audio over the past couple of months. This has come about since Hector Centeno released AmbiExplorer for Android, an application that lets us decode Ambisonic recordings for binaural playback in headphones.

AmbiExplorer plays back first-order B format files as well as UHJ encoded stereo files. As opposed to simply left, center, right, etc. a B format file is actually comprised of four channels known as W, X, Y & Z. These correspond to three directional signals and an omnidirectional reference signal.

By performing some matrix math on these signal in a coordinated fashion the entirety of the soundstage can be transformed in 3D space. AmbiExplorer decodes the four signals into a binaural feed, allowing the user to rotate their listening perspective in real-time. You can think of it as a 3-axis “balance” control.

AmbiExplorer is without question the easiest way to experience Ambisonic surround playback. It’s certainly a lot easier and less expensive than building an 8 channel playback cube like Hugh Pyle did.

When Mr Centeno initially released AmbiExplorer he announced it on the SurSound mailing list. I tried it immediately and found that it worked splendidly on my Nexus 4 and Nexus 7 (2013). The initial release could only playback B format files, so I sought out some samples from Ambisonia.

I’ve long been interested in the the theory of this technology, but never so bold or funded as to setup a full-fledged permanent listening environment. In truth, I’ve avoided it primarily because to have such as thing would compel me to go forth and try to start creating new recordings. A man can only have so many resource intensive hobbies.

Even so, I have purchased a number of commercial Ambisonic CDs over the years. All of these were in fact stereo CDs that were UHJ encoded.

Like the matrix Quad of old, UHJ encoding is a technique that allows the B format signals to be combined into one stereo-compatible track. A normal stereo just plays back the left/right pair. But feed that pair into a UHJ decoder and you can get back much of the soundfield information. A UHJ encoded recording doesn’t possess the height component, rendering it what is called planar surround.

Given my early success with AmbiExplorer I asked the author if he would consider adding UHJ decoding to the app, which he did relatively quickly. Lacking for the Y axis information you cannot perform Y axis transformations on such files, but it’s still a way to access a relatively large library of excellent commercial surround recordings.

Most of the Ambisonic material that you’ll find is classical music, choral music or sound effects. That fact limits it’s appeal in many circles, and would be the thing that could inspire me to want to create some original recordings of performances around Texas.

Until such time as my collected passions are funded by major lottery winnings I’m pacifying my curiosity with respect to surround sound recordings via the most excellent AmbiExplorer app and my small library of Nimbus CDs.

P.S. – The original release of Alan Parson’s Stereotomy album is a rare example of UHJ encoded popular music.