Decoding UHJ
A UHJ decoder, primarily for the 2-channel format, was the original component required for consumer experience of Ambisonics. When the system was first being promoted the push was two-pronged: on the one hand encouraging record companies to endorse the system and release discs (this was, in retrospect, ill-advised: record companies had been burned by quad systems and were not in a mood to endorse anything; and in any case, the people to persuade were engineers, producers and high-profile artists, who could use Ambisonic mixing equipment on sessions at will, just as they had a free rein in using other outboard studio equipment), while on the other hand encouraging hardware manufacturers to sign up as Ambisonic licensees and include decoders in their equipment.
Inside a UHJ encoder, the signals are processed in a phase amplitude matrix to recover a set of signals that resembles B-Format. In most cases the signal will actually be B-Format, but in the case of 2-channel UHJ there is insufficient information available to be able to reconstruct a true B-Format signal, only something that behaves in a similar way.
The information is then passed to an amplitude matrix that develops the speaker feeds, via a set of shelf filters, which improve the accuracy and performance of the decoder in smaller listening environments (they can be omitted in larger-scale applications). Ambisonics was designed to suit actual living rooms and practical speaker positions: most living rooms are rectangular and as a result the basic system was designed to decode to four loudspeakers in a rectangle, with sides between 1:2 (width twice the length) and 2:1 (length twice the width) in length, thus suiting the majority of living rooms. A layout control is generally provided to allow the decoder to be configured for the loudspeaker positions - an important aspect of Ambisonic replay where it differs from other surround systems: the decoder is specifically configured for the size and layout of the speaker array. The layout control may take the form of a rotary knob, a 2-way (1:2,2:1) or a 3-way (1:2,1:1,2:1) switch.
Four speakers is the minimum required for horizontal surround decoding and while this is suitable for a typical consumer environment, larger spaces require more speakers to give full surround localisation.
For more details on this topic, see Ambisonic decoding.Read more about this topic: Ambisonic UHJ Format