PROCESSORS- DOLBY PROLOGIC, DOLBY DIGITAL, and DTS
Today, there are four primary ways an audio signal can be processed, all of which are determined by how the signal was originally encoded:
Stereo- a separate left and right channel. This is available as long as the recording was made with two separate channels.
Dolby ProLogic- separates a Dolby Surround Sound encoded stereo signal (two channels) into four separate channels- One for the Front Right, One for the Front Left, One for the Center, and one for the Rear (both rear speakers get the same signal). While Dolby ProLogic does not provide a separate channel for Low Frequency Effects (LFE), a powered subwoofer can, and should, still be added for separate amplification of the bass frequencies.
Dolby Digital and DTS- include 6 separate audio channels. Five of these signals carry the full range of frequencies audible to the human ear (Front Right, Front Left, Center, Right Surround, Left Surround) and one signal carries only low end, or bass frequencies for special effects (sometimes referred to as the LFE channel- "Low Frequency Effect"). You will often hear the term "5.1" or "Five Point One" to describe this concept.
NOTE: Dolby Digital for home theater was originally referred to as AC-3 to distinguish it from the Dolby Digital intended for a regular movie theater. The difference is so slight that Dolby now prefers to simply call them both "Dolby Digital".
Only a digital source (DVD, Laser Disc, digital satellite or digital broadcast) can include these 6 separate channels. Dolby Digital and DTS are competing technologies based on the 5.1 concept. To learn more about Dolby Digital, go directly to the source, Dolby Laboratories.
WHAT ABOUT DTS?
Lately, there has been a great deal of confusion about the digital audio format known as DTS. DTS is similar to Dolby Digital in that it provides 5.1 separation. DTS is not a Dolby technology and is in fact a competitor. Both technologies use digital compression when recording the 5.1 information. The main difference between the two formats is that DTS utilizes less compression than Dolby Digital. Some say that this results in a "fuller" sound, while others say the difference is insignificant.
Many movies have been recorded in DTS and are played back in theaters which include DTS decoding. For home audio, however, Dolby Digital is more prominent for DVD's, although more and more DVD's are being produced with DTS Most hi end processors already include both Dolby Digital and DTS decoding.
DVD's have the capability of including up to eight audio tracks and according to Dolby Laboratories, Dolby Digital or PCM will always be provided on one track as the standard. This leaves the remaining tracks for additional languages, or other technology formats such as DTS.
A Listener's Guide to DVD Video (a nice article about audio on DVD's from Dolby Labs)
To learn more about DTS, visit them at www.dtsonline.com