DVD, like many other technical innovations, has brought up a few terms that might not be familiar to everyone. Hence we have created a glossary page where we try to explain those terms so they become understandable to everyone.

Please feel free to contact us if you have problems understanding any terms used in our reviews. We will be pleased to make them part of this glossary page.

Chroma Noise                                                                                                                                                       Everyone has probably watched an old video tape at one point or another. Have you ever noticed how the colors wash out and how red and blue colors seem to flicker? This phenomenon is called chroma noise, and it is inherent in the way video signals are currently transferred from the source to the monitor. DVD has a much better signal to noise ratio than any other medium available, but the studio should still pay attention during the transfer of a movie to the actual disc.

Pixelation                                                                                                                                                                     DVD discs contain compressed image data in order to fit a whole movie onto a single small disc. Sometimes this compression becomes visible, causing pixelation. In that case, the image seems to be slightly rougher for a brief moment. Pixelation can usually be avoided if the transfer to disc is done carefully. This is not an inherent limitation of DVD.

Pan & Scan, Letterbox, Widescreen                                                                                                                       While TVs usually have an aspect ratio of 4:3 (4 units wide, 3 units high), movies vary from 1.78:1 to 2.35:1 and almost anything in between. The result is that on a regular TV set, the movie must either be letterboxed, which creates black bars at the top and bottom of your screen to house the whole image, or the image is cropped on the left and right hand side to use the TV’s full height. Usually, when an important piece of the image drops out of the visible screen, the picture is panned to the side to show this piece, hence the term pan & scan. If you want to enjoy all the details of a movie, you should definitely prefer the widescreen letterboxed versions to the Pan & Scan alternative, because this is the way the filmmakers originally intended you to see the movie.

Open Matte                                                                                                                                                       To make things even worse, there is yet another display mode for movies. Sometimes, motion pictures are artificially made look like a widescreen version by simply covering the top and bottom parts of the image inside the theater’s projector. The resulting wide image resembles the ratio of an actual widescreen release. Sometimes these movies are re-released in a so-called Open Matte transfer, which means the covers are taken off, making the previously covered areas visible. What at first might look like a Pan&Scan version, can in fact be an open matte version, that does not lose any part of the image and in fact shows a lot more than the earlier theatrical matted widescreen version.

Anamorphic, 16x9 enhanced                                                                                                                                               One of the most confusing terms of DVD has to be the anamorphic 16x9 enhancement. DVD has the capability to store a lot more image information than your regular TV set can display, even though not all discs actually support this feature. So called 16x9 anamorphic TV sets can use this additional information to create a higher resolution image, resulting in a much sharper and more detailed picture. Since 16x9 screens have a widescreen ratio themselves, they do not have to bother about the black bars at the top and bottom of a widescreen movie and can thus stretch the image to use the full height of the display. If your TV does not support 16x9 enhancements, the movie will simply be displayed in widescreen.

Dolby Digital, AC-3                                                                                                                                               One of the technical specifications of DVD states that every disc must use at least one PCM or Dolby Digital soundtrack to ensure the medium’s high quality throughout all its publications. Dolby Digital is a sound format that allows to have up to six different channels of sound, making for a full surround experience of your movies. One of the most common used versions of Dolby Digital is its 5.1 channel implementation. Dolby Digital uses a compression scheme that is called AC-3 in order to store more information on a disc.

PCM                                                                                                                                               One of the technical specifications of DVD states that every disc must use at least one PCM or Dolby Digital soundtrack to ensure the medium’s high quality throughout all its publications. The DVD PCM sound format allows to have up to eight different channels of sound on a disc and is pretty much identical with the format used on your audio CDs, even though DVD supports much more detailed audio information than audio CDs do.

Dolby Surround                                                                                                                                               This is a relatively simple sound format that allows to bring surround effects into a stereo image, which allows you to use a regular stereo to reproduce the surround soundstage of a movie. Of course its quality is by far not as strking as that of a real 5.1 channel setup since a lot of the speakers are simply missing. However, it is a format that works fairly well for most people.

5.1 Channels                                                                                                                                               When speaking of movie surround sound, the term 5.1 channels comes up quite a lot. It simply means that the audio consists of 5 fully implemented channels and one channel that holds a bass signal only. This channel is used to drive subwoofers and since it is not making full use of the audio spectrum, it is called the .1 channel. The setup for a 5.1 channel system would generally consist of two front speakers, one center speaker for the dialog (also located in the front), two surround speakers in the back plus above mentioned subwoofer.

RSDL (Reverse-Spiral Dual Layer)                                                                                                                   This nice feature of DVD allows publishers to put even long movies onto a disc without you having to flip the disc. The player detects the end of one layer and automatically refocuses the laser to read from the second layer, which is underneath the first, slightly transparent one. The layer change might cause a slight jitter in the movie, which is so short however, that it is barely noticeable on most players, if at all.

Closed Captioned
This feature, which is very similar to subtitles, allows hearing impaired to follow the audio cue of a movie. A decoder displays dialogue and various sound cues on screen for people to read. Unlike subtitles, however, the captions are created by dedicated captioning companies who enter the movie’s script into a computer and then synchronise it with the images on screen through use of an internal time-code.

Aliasing Distortion
This phenomenon is only visible when you playback anamorphic, 16x9 enhanced discs on a regular TV set. The anamorphic transfer contains more horizontal lines than the standard 4:3 television set can display. The player automatically drops the lines that are too many. Under certain circumstances, this can lead to visible image distortions.

This is an enlarged part of an image that is encoded at the full anamorphic resolution. As you can see the edge is smooth and steadily going from one corner to the other.

This is the same image, but this time the player has removed certain lines to adjust the image to the 4:3 television set’s resolution. The way these lines have been dropped, leave a visible distortion, as you can see, as the edge is not smoothly going from one corner to the other any longer. It is jumping where the information from the anamorphic transfer is now missing.

Commentary Track
Commentary tracks are a feature that have first been introduced by Laserdiscs. Since Laserdiscs were mainly targeted at filmlovers who were interested not only in the film itself, but also in background information, commentary tracks became a highly acclaimed feature because they give the filmmakers the chance to actually talk about their work and explain certain scenes in detail. Commentary tracks, if available, are placed on a separate audio track on the disc and run throughout the film. The filmmakers are now talking about the movie you are watching, while it is running. The commentary itself was actually recorded, just as he or she was watching the film as well. The filmmakers now have the chance to rally comment and dissect every scene for its quality, importance, effect, etc. to give the audience a deep look into the film making process and the thoughts that go into it. Clearly commentary tracks are not for everyone, but if you especially like a film, they can offer very insightful and interesting information that would otherwise have never become publicly available.

DTS
DTS stands for “Digital Theater Systems” and is yet another sound format supported by DVD. Unlike the PCM and Dolby Digital formats however, it is not part of the DVD standard specifications and as such represents only an optional addition to the format. As a result, every disc that contains a DTS soundtrack also has to feature an alternative PCM or Dolby Digital track.
DTS, like Dolby Digital, is a multichannel surround format that uses compressed information for its 5.1 discrete channels, however it uses much less compression to achieve its goal and as result uses up substantially more space on the disc, while at the same time offering a better representation of the original material. Whether you can truly hear this difference is subject to a vast number of heated debates. DTS soundtrack require DTS capable equipment for playback, which currently comes at a substantial premium over more readily available Dolby Digital equipment.

THX
A lot of confusion is surrounding THX. It is not a sound format and it is not a special image format. THX is a Lucasfilm company that is certifying films, software and hardware, and as such making sure the presentation quality meets certain standards. THX certified films or equipment are not necessarily better than parts that do not carry THX’s seal of approval, but at least you have some kind of a guarantee that it meets certain quality aspects.

THX EX
THX EX is the name of a new Dolby Digital sound format, using 6.1 channels. The format adds an additional surround center channel to the current 5.1 setup to create a more engrossing surround field that is compatible to the front field in terms of spatial integration. Unlike sound formats like DTS,THX EX does not necessarily require additional equipment to listen to the audio track. It is an extension and as such backwards compatible with the current Dolby Digital standard. If you do not have a THX EX decoder in your home theater setup, the playback will be automatically converted for 5.1 playback.

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