What is the difference between Dolby ProLogic, Dolby ProLogic II, Dolby Digital (AC3, 5.1) and DTS audio surround sound technology?

Surround sound consists of multi-channel audio. Different surround sound types encode and decode this audio differently.

Dolby® ProLogic technology
This consists of four discrete channels of audio (left, right, center and rear). This matrix multi-channel sound is encoded down to two channels for distribution, and then is decoded back to four channels when played back on a stereo source that decodes Dolby ProLogic technology surround.

Dolby ProLogic II technology
Processes the standard four channel Dolby ProLogic technology signal to reproduce 5.1 channel surround.

Dolby Digital (AC3, 5.1) technology
This is a multi-channel surround system that contains 6 discrete channels of audio (left front, right front, center, left rear, right rear and LFE subwoofer). Dolby Digital technology is commonly referred to as 5.1 (five point one) surround sound because it contains 5 full bandwidth (20 - 20,000 Hz) for the front, center and rear speakers, and one low frequency effects (LFE) subwoofer channel that is referred to as .1 (point one).

DTS™ Digital Theater Sound
This is an encode/decode system that delivers 6 discrete channels (5.1) of high quality 20 bit audio. Each of the 5.1 channels of decoded 20 bit DTS audio is superior to the linear 16 bit PCM audio used for conventional compact discs. DTS audio data is not as compressed as Dolby Digital technology. The same amount of audio encoded in Dolby Digital technology will use less disc space than if it was encoded in DTS.

DTS ES Matrix
This is actually a 5.1-channel format with the back surround audio channel matrixed into those of the right and left surround. The back surround channel is matrixed in similar fashion as the front center channel is matrixed into the front right and left channels in the Dolby Surround Pro-Logic technology. As such, the back surround channel is not discrete and therefore is not a true '6.1' format. DTS-ES Matrix is compatible with THX Surround EX equipment. DTS-ES Matrix is completely backwards compatible with DTS 5.1 equipment.

DTS ES Discrete 6.1
This is a true 6.1-channel format, as the back surround audio channel is discretely encoded into the DTS bitstream. This format offers better stabilization over the surround channels for complete 360-degree sound localization and surround pans (i.e., movement of sound in the surround channels from one side to another). A data flag signals the decoder (usually part of the receiver or pre-amplifier) that the bitstream contains an extra discrete back surround channel. For backwards compatibility, DTS-ES Discrete 6.1 back surround channel is ignored by DTS 5.1 equipment.

DTS Neo:6

This is a 7.1 configuration with two rear-center speakers that play in mono. The DTS Neo:6 works a lot like Dolby Pro Logic IIx where you can take stereo content and up-convert the sound to 5.1 or 6.1 channel surround sound format.

DTS 96/24

This allows the delivery of 5.1 channels of 24-bit, 96 kHz audio and high-quality video on the DVD Video format. DTS 96/24 also can be placed in the video zone on DVD-Audio discs, making these discs playable on all DTS-compatible DVD players. This format is implemented as a core DTS stream along with an extension containing the deltas which enables the 96/24 sound reproduction.

DTS-HD High Resolution Audio

DTS-HD High Resolution Audio and DTS-HD Master Audio compose the DTS-HD extension to the original DTS audio format. This is a lossy compression that delivers up to 7.1 channels of sound at a 96 kHz sampling frequency and 24-bit depth resolution. This format is supposed to be an alternative for DTS-HD Master Audio when disc space may not allow it. DTS-HD High Resolution Audio is selected as an optional surround sound format for Blu-ray Disc™ (BD) and HD DVD media, with constant bit rates up to 6.0 Mbit/s and 3.0 Mbit/s respectively.

DTS-HD Master Audio

This is a lossless audio codec, previously known as DTS++ and is steadily becoming the standard for Blu-ray lossless audio. It is the second of two DTS-HD audio formats. This format supports an unlimited number of surround sound channels, and can downmix to 5.1 and 2-channel. This format also can deliver audio quality at bit rates extending from DTS Digital Surround up to lossless (24-bit, 192 kHz).