Audio/Video (AV) Receiver Specifications and Terminology - What do They All Mean? (Page 2 of 4)

A/V receiver specifications usually list the types of surround sound decoding of which they are capable. Of course, you first need a source that contains the encoded stream that also uses the same decoding scheme. Since different sources have different encoding modes, it is desirable that an audio/video receiver support several different modes.

For example, Dolby True HD and Digital Plus are recent decoding methods found on some newer Blu-ray discs. If your future plans include an investment in Blu-ray, these would be very desirable decoding modes to have. As another example, if you have a large library of CD audio or DVD videos, Dolby Pro Logic would be a good feature.

In general, it's better to have a high-end surround sound decoding feature that you don't need yet than to settle for an alternate less-capable process. (This variation in decoding features is why most DVDs and Blu-ray discs have multiple encoding.)

First proposed in 1990, Dolby Digital became the default audio format for DVDs and HDTV, as well as for some satellite TV broadcasting. It is a "5.1" system consisting of right, left, and center front speakers, and two right and left rear speakers. The .1 refers to the subwoofer, or very low frequency output. The subwoofer is an important element in providing an immersive listening experience in a home theater, allowing sound pressures that can be felt as well as heard. As this is the oldest standard, all A/V receivers should be expected to support it.

This, by the way, does not preclude using the receiver with fewer speakers. 2.1 and 4.1 would still be decoded and sent to the proper speakers.

Dolby Digital EX provides 6.1. It adds a sixth channel obtained from mixing together the right and left surround channels. Of course, the receiver should have six powered speaker outputs in order to support this encoding mode. EX is beneficial because it increases the sound pressure, again, helping to provide that immersive experience.

Dolby Pro Logic II and IIx are encoding standards that create surround sound from any stereo source, including analog signals from phonographs and VCRs. It works by slightly changing the phase and delay of the sounds going to each channel. This increases the stereo separation and can simulate a multi-channel soundtrack using two front and two rear speakers.

Found only on some newer Blu-ray discs, Dolby Digital Plus provides 7.1 channel audio. It is presented in a faster data stream than Dolby Digital, with less compression, and thus it is more realistic and accurate than what can be obtained from standard DVDs. You'll need an HDMI input in order to decode this.

Also found only on some newer Blu-ray discs, Dolby True HD supports 7.1 channel audio and uses "lossless compression" that provides a more accurate reproduction than Digital Plus. Again, an HDMI input is required in order to decode this.

Think "movie theaters." That's where this 5.1 digital audio format came from. It stands for "Digital Theater Systems" and the standard is owned by DTS, Inc. Very few DVD or CDs support DTS, but some DVD players and A/V receivers do support it. (It was also briefly popular on Laserdiscs - right before DVDs supplanted them.)

DTS ES adds a one or two speaker back surround channel, making the output 6.1.

DTS Neo:6, like Dolby Pro Logic, works with standard stereo audio, except that it generates 6.1 and has different modes for movies and music.

Brought to us by the folks at Lucasfilm, this all-encompassing standard includes requirements for construction, compatibility, user interface, and, of course, audio performance. Most home users interested in this encoding format would look at the "THX Select" certification. This covers up to 2,000 square feet. "THX Ultra" increases the coverage to 3,000 square feet.

Few A/V receivers support THX encoding. Those few that do currently range in price from about $800 to over $5,000.

Next: Standard Ports and Connections