Ambisonic UHJ format
Although UHJ permits the use of up to four channels (carrying full-sphere with-height surround), only the 2-channel variant is in current use (as it is compatible with currently-available 2-channel media).
UHJ is a unique hierarchical system of encoding and decoding directional sound information within Ambisonics technology.
Depending on the number of channels available, the system can carry more or less information – but at all times, UHJ is fully stereo- and mono-compatible.
In its most basic form, two-channel (L, R) UHJ, horizontal (or "planar") surround information can be carried by normal stereo signal channels – CD, FM or digital radio, etc.
Adding a fourth channel (Q) to the UHJ system allows the encoding of full surround sound with height, known as Periphony, with a level of accuracy identical to four-channel B-Format.
*These designations are seldom used today 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.
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).
Because of the inter-channel phase relationships inherent in the encoding scheme, the listener experiences stereo that is often significantly wider than the loudspeakers (see also § Undecoded UHJ below).
Some engineers have preferred the perceived additional spaciousness, width and stability of undecoded 2-channel UHJ to conventional panpotted stereo mix techniques.
Similarly, on the Tina Turner album, Break Every Rule, the backing vocals are in fact UHJ encoded - and in this case there is no point in the listener decoding the tracks, because the rest of the mix is in regular panpotted stereo and contains no surround information - the vocals were encoded purely for the spacious effect without decoding.
A significant number of 2-channel releases were made with this equipment, including several albums on the KPM production music library label, and commercial releases such as Steve Hackett's Till We Have Faces, The Alan Parsons Project's Stereotomy, Paul McCartney's Liverpool Oratorio, Frank Perry's Zodiac, a series of albums on the Collins Classics label, and others, most of which are available on CD.
However, the remastering - and in some cases release - of original 2-channel UHJ recordings in G-Format has proved to be surprisingly effective, yielding results at least as good as the original studio playbacks, thanks primarily to the significantly higher quality of current decoding systems (such as file-based software decoders) compared to those available when the recordings were made.
