Super Stereo
A disadvantage of the use of 2-channel UHJ is that to obtain a surround effect the listener requires an Ambisonic UHJ decoder. These have traditionally not been widely available. However, listeners to a 2-channel UHJ signal without a decoder notice a "super stereo" effect.
Because of the inter-channel phase relationships inherent in the encoding scheme, the listener experiences stereo that is often significantly wider than the loudspeakers.
At the same time, a feature of domestic UHJ decoders has been the inclusion of a super stereo feature. This allows conventional stereo signals to be "wrapped around" the listener, using some of the capabilities of the decoder. A control is provided that allows the width to be varied between mono-like and full surround. This provides a useful capability for a listener to get more from their existing stereo collection.
Both features were used as selling points in the early days of Ambisonics, and especially Ambisonic mixing. They helped to overcome a "chicken and egg" situation where record companies were reluctant to release Ambisonic recordings because there were few decoders in the marketplace, while hi-fi manufacturers were unwilling to licence and incorporate Ambisonic UHJ decoders in their equipment because there was not very much mainstream released content. On the one hand, it was worth having a decoder because you could get more out of your existing (stereo) record collection; while on the other it was worth making UHJ recordings because even people without a decoder could gain appreciable benefits.
Read more about this topic: Ambisonic UHJ Format