Each of the two competing high definition DVD formats have specs built in for two new surround sound formats: Dolby Digital Plus and DTS-HD.

Today's DVDs have enough space for an audio stream of 448kbps (448,000 bits per second) - By comparison, DTS has a rate of 1.5Mbps. (1,500,000 bits per second.)

Confused yet? Just know that compression is the scheme where the audio is deconstructed and reconstructed in a way that uses less space. Certain ways of doing that are superior to other ways, but are "lossy" in that some material is, uh, lost, in the process. One method offers a perfect reconstruction, and is called "lossless."

On to Dolby Digital Plus: This has better more efficient coding for the compression, higher bitrates, more channels of audio (up to 13.1). The higher bitrate means better sound quality. Dolby Digital Plus will be backwards compatible with (old) Dolby Digital if that's what your receiver can handle, but even that will contain about 30% more bits than the old way.

Introducing Dolby TrueHD: another advance. While Dolby Digital Plus throws away some bits in the compression scheme, Dolby TrueHD has what's called a "lossless" compression scheme... which reconstructs what was heard in the studio. Exactly. If you see a High Definition DVD with Dolby TrueHD on it, you will know you can hear what the studio did (provided your system is good.)

THX: (now renamed THX Ultra... see below.) Now, about soundtracks: movie soundtracks are equalized for movie theaters. Ah ha. Movie theaters are generally dead acoustically and even more dead when filled with high frequency-absorbing human bodies. Plus, high frequencies fade with distance (as in: to the screen) The THX specification for home theater (developed by Lucasfilm) does 4 things:

It cuts high frequencies some. Why? Because they were boosted for the movie theater dead - absorbent - environment. Without THX your soundtrack at home would be shrill.

It adds a sense of spaciousness to your surround channels. Many DVD soundtracks' surround channels (rear speakers) are in mono, not stereo. If in stereo, the circuit recognizes that and does nothing.

It rolls off bass to the main speakers at 80 cycles and routes bass to the subwoofer.

It certifies amplifier power and performance as sufficient.

But, there's more. There's ALWAYS more.

THX SELECT: does the above but lowers amplifier standards. So it can be in cheaper gear. But then they decided to rename 'standard' THX to "THX Ultra."

Think we're done? Cue Jack N: "You can't handle the truth!"

Now there's THX Ultra2, which addresses the VIDEO switching circuitry, creates 7.1 channels from 5.1 sources, and compensates for when the speakers are right up against the walls.

DTS will be mandatory on Blu-Ray discs. DTS-HD will be optional and backward compatible. DTS will be at 2.5 times the data rate of Dolby Digital.

DTS-HD does 7.1 with zero loss.

What it all mean?

The new High Definition DVDs will sound better than you've heard from any DVD so far.