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 loudspeaker positions, and offers the listener a considerable degree of flexibility as to the layout and number of speakers used for playback.

Ambisonics was developed in the UK in the 1970s under the auspices of the British National Research Development Corporation.

Higher-order Ambisonics

Visual representation of the Ambisonic B-format components up to third order. Dark portions represent regions where the polarity is inverted. Note how the first two rows correspond to omnidirectional and figure-of-eight microphone polar patterns.

The spatial resolution of first-order Ambisonics as described above is quite low. In practice, that translates to slightly blurry sources, but also to a comparably small usable listening area or sweet spot. The resolution can be increased and the sweet spot enlarged by adding groups of more selective directional components to the B-format. These no longer correspond to conventional microphone polar patterns, but rather look like clover leaves. The resulting signal set is then called Second-, Third-, or collectively, Higher-order Ambisonics.

 

Impulse Response (IR) Recordings

In signal processing, the impulse response, or impulse response function (IRF), of a dynamic system is its output when presented with a brief input signal, called an impulse. More generally, an impulse response refers to the reaction of any dynamic system in response to some external change. In both cases, the impulse response describes the reaction of the system as a function of time (or possibly as a function of some other independent variable that parameterizes the dynamic behavior of the system).

In the case of this project IR responses were measured using a bespoke technique to yield seperate IRs for 1st order ambisonic W,X,Y and Z channels.

The resulting IR samples can be used to convolve a dry 1st order ambisonic signal to apply the reverb of the captured space.

 

Citations:

Ambisonics. (2016, March 2). In Wikipedia, The Free Encyclopedia. Retrieved 14:19, March 16, 2016, from https://en.wikipedia.org/w/index.php?title=Ambisonics&oldid=707963589

Impulse response. (2016, January 20). In Wikipedia, The Free Encyclopedia. Retrieved 14:22, March 16, 2016, from https://en.wikipedia.org/w/index.php?title=Impulse_response&oldid=700840818