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AES

Audio Engineering Society

24th International Conference on Multichannel Audio
June 26-28, 2003, Banff, Canada

 

SURROUND AMBIOPHONIC RECORDING AND REPRODUCTION

by Ralph Glasgal

AMBIO PLAYBACK OF 5.1 DISCS (fig. 4)

Home theater surround movies or music recordings can be played back Ambiophonically rather than stereophonically in a manner analogous to the playback of CDs and LPs, discussed above. (The psychoacoustic disadvantages of the LCR reproduction scheme are reviewed in the appendix.) The left and right frontal 5.1 channels can be fed directly to a crosstalk canceller and thence to an Ambiopole. An Ambiopole can also be used simultaneously as a center speaker pair simultaneously and so it is an easy matter to add the unaltered center information to the other two Ambiophonic signals. One can also imagine a home theater processor equipped to drive two center speakers with a switch to go between stereo LCR and the CC Ambiopole. Certainly, it is easier to set up the front part of a home theater system using just two center speakers 20 or 30 degrees apart so as not to stand in front of the TV screen than setting up three speakers that must be equidistant and spaced symmetrically. Also, for home TV, viewers like to be centered so the major supposed advantage of the LCR arrangement seems of limited value.

Figure 4   Ambiophonic Playback of 5.1 Material

The two rear surround channels go to a second crosstalk canceller and a rear Ambiopole. For many movies this arrangement produces a rear stage with excellent localization over some 160 degrees in the rear. Of course, this applies only to movies that were recorded in stereo in the rear, not just dual mono or fabricated sound effects, or ambience. Music DVDs often include real hall ambience captured during the performance and again, if not mono, can provide an ambient field spread across the rear. While not ideal, since ceiling rear and frontal ambience comes from this horizontal rear arc, this effect is better than the standard ITU plus and minus110-degree arrangement whose properties are discussed in the Appendix.

Better yet, for much music, where there are no instruments or vocals in the rear, the rear surround channels can be ignored and the more natural ambience generated by the Ambiovolver can be used instead free from the constraints of the ITU surround speaker position mandate. It is also possible to use both the Ambiovolver and the rear Ambiopole simultaneously. For those who want applause coming from the rear, this arrangement works well for both live music and movies.

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