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Sennheiser Ambeo for VR Sound

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AMBEO for Virtual Reality

There is probably no other application with a more obvious need for three-dimensional spatial sound than Virtual Reality and 360° videos: In order to maximise the immersive experience the audio must also be spatial. No matter whether you are producing immersive content for VR goggles, your favorite web browser, YouTube 360, facebook 360 or for gaming, Sennheiser’s front-end VR Mic captures the full spherical sound at a single point in space.

 

Capturing in Ambisonics

For 3D audio in general we distinguish between Channel-based, Object-based or Scene-based representations of the sound field. Channel-based audio delivers its content to a physical loudspeaker layout, with one output channel for each speaker playback, such as Left and Right for Stereo. Object-based audio describes where a certain audio object is placed in the sound field and data processing calculates its playback to specific 3D speaker systems, such as Dolby Atmos.

Sound for Virtual Reality today relies on scene-based capturing, which is a way to capture a specific point in the sound field. Commonly accepted methods are binaural, quad binaural or Ambisonics. Binaural uses a dummy head with microphones placed within an artificial ear, whereas quad binaural requires four sets of binaural dummy heads. Both techniques will capture the sound field with pre-rendered binaural information and gives static binaural playback on standard stereo headphones.

Ambisonics, on the other hand, is a channel-independent representation of the sound field. It is a 3D sound format that captures the full spherical sound field signature, thereby providing an enveloping surround sensation, not only in the horizontal plane, but also including height information. It can be decoded to any existing, or future, speaker layout and also allows for dynamic binaural playback on headphones by applying a Binaural Renderer including Head-Related Transfer Functions (HRTF).

The Sennheiser VR Mic works in First Order Ambisonics. The microphone has four identical condenser capsules in a tetrahedral cluster with a native Ambisonics A-format output , which needs to be converted into Ambisonics B-format. This can be done with the free Sennheiser AMBEO A-B format converter, which is a plug-in to your preferred Digital Audio Workstation.

The First Order Ambisonics B-format is a W, X, Y, Z representation of the sound field. W is a sum of the four capsules, whereas X, Y and Z are virtual bidirectional microphone patterns representing front/back, left/right and up/down. Therefore any virtual direction from the microphone can be perceived by the listener during playback of Ambisonics B.

Where to best position the microphone? An Ambisonics microphone’s location determines its perspective of the sound field. Preferred common practice is mounting it as close to the camera as possible, giving audio and video the same point of capture. Be careful to place it outside the field of view or be prepared to stitch it out in the video post-production. Also, when placing the VR Mic below or above the camera, be careful that the camera rig will not shadow the sound or create unwanted reflections or diffraction to the sound. Using a “magic arm” or other fixture to attach it to the camera will be useful.

The AMBEO VR Mic requires a four-channel field recorder with four identical recording channels, all providing 48V phantom power. Set the channel gains to exactly the same level, preferably using digital gain setting and linking the four channels, otherwise the sound field imaging will be distorted. We recommend testing the levels of the four channels using a phantom-powered tone generator.

 

The elegantly designed AMBEO® VR Mic has been developed in cooperation with VR content producers and fine-tuned through an extensive creators’ program with participants from across the audio and VR communities. The mic caters exactly to the needs of VR content creators, letting you capture the experience and spirit of any location enabling the listener to be immersed as if they were there.

 

 

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