OTHER TECH

Today's home theater receivers can decode many surround sound formats and offer various kinds of multichannel processing. These are the most common.

Dolby Digital This format should be familiar, since it's used in most movie theaters and on most DVDs. It can deliver up to five main channels - left, center, and right front and left and right surround - plus a deep-bass-only ".1" channel.

Dolby Digital EX creates a back surround channel from a 5.1-channel Dolby Digital mix for an improved sense of sound effects moving from front to back (or vice versa) and to make sounds placed behind the listener more realistic.

Dolby Pro Logic II (DPL II) and IIx decode VHS tapes and many TV broadcasts that use the older Dolby Surround format, providing front left, center, and right channels plus a single surround channel in the back. DPL II can also generate 5.1-channel sound from any stereo or Dolby Surround source, and DPL IIx takes this a step further by deriving a back surround channel for 6.1- or 7.1-channel playback. Both versions can provide separate listening modes for music and movies as well as several parameters than you can adjust yourself (but not all receivers have all of these options).

Dolby Virtual Speaker and Dolby Headphone can simulate 5.1-channel playback with just two speakers and a subwoofer, or multichannel surround sound from a set of headphones.

DSP (digital signal processing) surround modes Most surround receivers provide several DSP modes meant to enhance music listening with artificially generated ambience.

DTS Digital Surround Popular in movie theaters and similar to Dolby Digital 5.1, DTS is found as an alternative to Dolby Digital on many DVDs.

DTS-ES Like Dolby Digital EX, this adds a back surround channel to DTS 5.1 soundtracks, but unlike EX, DTS-ES consists of seven (6.1) discrete channels.

DTS Neo:6 Like DPL IIx, this can create six main channels plus a bass-only channel from two- and four-channel sources.

THX Surround EX Decodes Dolby Digital EX 6.1-channel soundtracks with various enhancements, like "decorrelating" the single back surround channel for 7.1-channel systems so it becomes a pair of discrete channels.