Research into Upmixing

Upmixing is a technique used to convert mono or stereo into 5.1 surround sound. This is an interesting technique to consider in relation to my project as it could mean the possibility of not having to record the event in 5.1 but rather in stereo and then convert it to surround sound. However the upmixing does not create a "true" 5.1 image but gives it a larger sense of space by adding information to the rear speakers of the 5.1 array.

• It would be interesting to consider testing a 5.1 recording with a stereo version that has been upmixed. The results would show wether people can tell the difference between the two techniques and which one is preferred by the listener. This would indicate wether it is worth going to the expense of recording an event in 5.1 or upmix a stereo recording. 

"There are lots of ways of expanding stereo material to 5.1, but most techniques are based on those developed for converting mono to stereo. The most common approach seems to be to allocate the original stereo channels to the left and right channels of the 5.1 array, and then derive centre and surround channels. The derivation of centre and surround channels may remain unchanged throughout the track (the usual technique for classical music), or may change — perhaps to emphasise specific sections, such as the choruses in popular music. Of course, by retaining the original left and right channels, the end-user can easily get back to the original stereo if they don't like the upmixed surround version.
Techniques vary widely, but the centre channel is typically a mono sum of left and right, possibly with a little equalisation and maybe a touch of extra delay. The surrounds are usually derived from left minus right (and vice versa), again with some delay and EQ, and possibly some extra reverb. Much hushed talk surrounds the production of upmixed 5.1 mixes from stereo, but as you can see, it's not really rocket science, merely a way of arranging material from a completed two-channel stereo mix such that it plays back over all six channels of a 5.1 playback system. There are also several products on the market now — such as TC Electronic's System 6000 — which incorporate dedicated algorithms specifically to convert stereo material to 5.1. The results depend on the source material, but often the upmixed version is very credible and pleasant to listen to."

You Are Surrounded, Surround Sound Explained- Part 5, Hugh Robjohns, December 200, Sound on Sound Magazine