Science & Technology

With the advent of Digital Versatile Disc or Digital Video Disc (DVD) people are increasingly becoming aware of the various sound technologies associated with it. There were times wherein one will be content with a 30W tape recorder which would give even a high fidelity sound from a audio cassette as garbage.

VCD, LCD's couldn't create that much of a sensation among the public. The video and audio information stored on a DVD-Video are pure digital for a crystal clear picture and CD-quality sound. It is the ideal format for movie viewing and collecting. The DVD format provides up to 480 horizontal lines of resolution. This is a significant improvement over 260 horizontal lines of resolution of standard VHS. The color is brilliant, rich, and saturated, accurately rendering skin tones. With the right equipment and set-up, you can enjoy a picture that approaches the quality of film. All DVD-Videos include Dolby Digital surround sound, consisting of up to six and seven channels of surround sound (i.e., Dolby Digital 5.1-channel and 6.1-channel surround sound). Additionally, some DVDs contain an additional alternative surround sound format, called DTS Digital Surround.

Sound and picture are the two integral parts while watching a DVD. If either of those two are compromised, then the overall performance of the DVD movie will be equal to watching a movie in VHS. One of the element, Sound is analyzed in depth in this article.

Surround sound refers to the use of multiple audio tracks to envelop the movie watching or music listening audience, making them feel like they're in the middle of the action or concert. The surround sound movie soundtrack allows the audience to hear sounds coming from all around them, playing a large part in realizing what movie makers call "suspended disbelief". "Suspended disbelief" is when the audience is completely captivated by the movie experience and is no longer aware of their real-world surroundings.

True surround sound algorithms rely on dedicated speakers that literally and physically surround the audience. There is one center speaker which carries most of the dialog (since the actors usually speak while making their on-screen appearance), and part of the soundtrack. There are left and right front speakers that carry most of the soundtrack, and may carry parts of the dialog (when the director wants to intentionally off-set the source of the dialog to either side, from its default dead-center screen location). There is a pair of surround sound speakers that is placed to the side (and slightly above) of the audience to provide the surround sound effects. Finally, a subwoofer can be used to reproduce the low and very low frequency effects (LFE) that come with certain movies (e.g., the foot-stomping bass effects in Jurassic Park and Godzilla).

There are virtual surround sound algorithms (e.g., Sound Retrieval System [SRS], and other proprietary algorithms) that make use of only two left and right speakers and psycho-acoustics effects to emulate true surround sound formats. For the purposes of our discussion, these so-called virtual surround sound algorithms are excluded for now.

Dolby Digital (formerly known as Dolby AC-3, AC-3is short for audio coding 3) is the de facto surround sound standard in today's home theaters.It is the surround sound format used in thousands of movie theaters today. And, since about the mid-1990's, it has become available for home theater use by consumers. Today, a large percentage of the DVD-Video titles come with Dolby Digital surround sound. (Dolby Digital content first appeared on LaserDisc, since DVDs emerged in the Spring of 1997. Hi-Fi VHS still only supports up to Dolby Surround Pro-Logic.)

Not only is Dolby Digital the standard for DVD-Video, but it is also part of the new High Definition TV (HDTV) standard. It is used in pay-per-view movies of digital satellite broadcasting (e.g., DIRECTV system). Dolby Digital is the successor to Dolby Surround Pro-Logic.

The Dolby Digital, or "Dolby Digital 5.1-channel" surround sound, format provides five discrete (independent) channels (center, left, right, surround left, surround right; giving it the "5" designation) of full frequency (with respect to the range of human hearing, which ideally ranges from 20 Hz to 20,000 Hz) effects, plus a sixth channel for low frequency effects (LFE), usually reserved for the subwoofer speaker. The low frequency effects channel gives Dolby Digital the ".1" designation. The ".1" signifies that the sixth channel is not full frequency, as it contains only deep bass frequencies (3 Hz to 120 Hz).

An alternative and competing format to Dolby Digital is DTS Digital Surround, another 5.1-channel surround sound format. DTS offers higher data rates than Dolby Digital, leading many home theater enthusiasts to claim that DTS is better than Dolby Digital in sound quality. Unfortunately, there are not as many DVD-Video titles with DTS surround sound as compared to those with Dolby Digital.

Dolby Surround Pro-Logic emerged in home theater systems in the early 1990's. It became the surround sound standard for Hi-Fi VHS, and is still the standard for today's analog TV broadcasts, since the Dolby Surround Pro-Logic signal can be encoded in a stereo channel. If you have an "older" Dolby Surround Pro-Logic receiver, you can still enjoy movies on DVD-Video, since all DVD-Video players down-mixes the Dolby Digital information to the Dolby Surround Pro-Logic format, and outputs the signal as a stereo audio pair.

THX Surround EX™ & DTS Extended Surround™ (DTS-ES™)

Just when you thought 5.1-channel Dolby Digital and DTS were enough, at the leading edge today are two new "Extended Surround" formats, namely THX Surround EX™ and DTS Extended Surround™ (or DTS-ES™ for short). THX Surround EX is jointly developed by Lucasfilm THX and Dolby Laboratories, and is the home theater version of "Dolby Digital Surround EX™", an Extended Surround sound format exclusively for selected movie theaters. THX Surround EX is the Extended Surround version of Dolby Digital 5.1, while DTS-ESJust is that of DTS 5.1.

The difference between the new Extended Surround formats and their 5.1-channel surround sound counterparts is the addition of a surround back channel, whose corresponding speaker is placed behind the audience. This allows certain soundtrack effects to be presented behind the audience, thereby achieving complete 360° surround sound. (Remember that in the 5.1-channel surround sound formats, the surround speakers are placed on either sides of the audience--not behind them.)

Both THX Surround EX and DTS-ES Matrix surround sound encode the surround back channel information into the surround left and surround right channels (similar to the way the center channel is encoded for Dolby Surround Pro-Logic). This encoding is referred to as matrixed, since the surround back channel is derived from those of the surround left and surround right channels. Because of this matrix encoding scheme, the surround back channel is not a true discrete channel.

DTS-ES can optionally support a fully discrete surround back channel. That is, the surround back channel is truly independent from those of the surround left and surround right channels. This is called DTS-ES Discrete 6.1 (as opposed the its matrix counterpart, DTS-ES Matrix).

The Extended Surround formats are commonly referred to as "6.1"-channel surround sound. Strictly speaking, THX Surround EX and DTS-ES 6.1 Matrix are not true "6.1"-channel, since the "6" implies a sixth fully discrete channel. They are really 5.1-channel surround sound formats, designated as 5.1 EX or 5.1 ES, respectively. (That's why we put quotes around the "6.1".) Only DTS-ES 6.1 Discrete is a true 6.1-channel surround sound format.

The Extended Surround formats are completely backwards-compatible with their 5.1-channel counterparts (i.e., THX Surround EX is backwards compatible with Dolby Digital 5.1, and DTS-ES is backwards compatible with DTS 5.1). In order to hear the Extended Surround formats, you will need a THX Surround EX and/or DTS-ES decoder (this is usually a function of the receiver or pre-amplifier), six channels of amplification, and another speaker for the surround back channel. Rest assured, you can still use your existing (or a soon-to-be-purchased) DVD-Video player, as long as it features Dolby Digital and DTS digital output.