Google Patent | Ambisonics Sound Field Navigation Using Directional Decomposition and Path Distance Estimation
Publication Number: 20190020967
Publication Date: 2019-01-17
Techniques of rendering sound for a listener involve determining, at a first position, a set of directions from which some specified fraction of the sound field energy originates and reconstruct the sound field at a second position based on the set of directions. Along these lines, a sound rendering computer may receive sound data representing sound emanating from positions on a sphere centered on a microphone. Nevertheless, only a small fraction of these points on the sphere contribute much of the sound field energy directed at the listener. The sound rendering computer determines such directions using a directional decomposition in which those directions having the highest fraction of the sound energy are identified. When the listener moves away from the microphone’s position, the sound rendering computer, after identifying such directions, applies an amplitude and phase factor to the sound fields corresponding to those directions.
Ambisonics is a full-sphere surround sound technique: in addition to the horizontal plane, it covers sound sources above and below the listener. Unlike other multichannel surround formats, its transmission channels do not carry speaker signals. Instead, they contain a speaker-independent representation of a sound field called B-format, which is then decoded to the listener’s speaker setup. This extra step allows the producer to think in terms of source directions rather than in terms of directional signal positions, and offers the listener a considerable degree of flexibility as to the layout and number of speakers used for playback.
In ambisonics, an array of virtual directional signals surrounding a listener generates a sound field by decoding a sound file encoded in a scheme known as B-format from a sound source that is isotropically recorded. The sound field generated at the array of virtual directional signals can reproduce the effect of the sound source from any vantage point relative to the listener. Such decoding can be used in the delivery of audio through headphone speakers in Virtual Reality (VR) systems. Binaurally rendered high-order ambisonics (HOA) refers to the creation of many directional signals which combine to provide a pair of signals to left and right headphone speakers.
In one general aspect, a method can include receiving, by controlling circuitry of a sound rendering computer configured to render sound fields for a listener, sound data resulting from a sound field produced by directional signal sources at a first position in space, each directional signal source producing a directional signal contributing to the sound field. The method can also include identifying, by the controlling circuitry, a plurality of directions of the directional signal sources based on the sound data, the plurality of directions being directions by which at least a specified fraction of energy of the sound field is produced at the first position. The method can further include obtaining, by the controlling circuitry, a plurality of distances of the directional signal sources from the first position in space. The method can further include generating, by the controlling circuitry, the sound field at a second position based on the plurality of directions and the plurality of distances, the second position being different from the first position.