With respect to soundtracks, such as those on movies and DVDs, 5.1 means that the soundtracks are recorded with five main channels: left, center, right, left surround, and right surround, plus a low-frequency effects (LFE) bass channel (called a ".1" channel because it covers only a fraction of the frequency range of the main channels).

Some movie soundtracks use a variation on 5.1 called Dolby® Digital Surround EX™, which has now migrated via DVDs to home theater. This format matrix encodes a third surround channel onto the left and right surround channels of 5.1 soundtracks, and may be decoded or not at the cinema’s or home listener’s option due to their inherent compatibility. Because the extra surround information is carried on the left and right surround channels, Dolby Digital Surround EX encoded soundtracks are still regarded as 5.1 soundtracks.

With respect to home playback, the terms 5.1, 6.1, and 7.1 mean that there are five, six, or seven main speakers, plus a subwoofer, in the playback system. (The subwoofer reproduces the LFE channel recorded on 5.1 soundtracks, plus any bass the main speakers cannot handle.) The difference is in the number of surround speakers: two in a 5.1 system, three in a 6.1 system, and four in a 7.1 system.

Obviously, a 5.1-channel soundtrack can be played on a 5.1-speaker system. But it is not always understood that it can also be played on a 6.1- or a 7.1-speaker system. To do this, the two surround signals on the 5.1 soundtrack are spread across the three or four surround speakers. This distribution can be accomplished by a Dolby Digital EX decoder, a THX Surround EX decoder, or other proprietary methods provided in home theater equipment by various manufacturers.

So the number (i.e., 5.1) describing the soundtrack does not have to match the number applied to the speaker system. It’'s even possible to play two-channel stereo content over these multi-speaker systems by using a matrix surround decoder such as Dolby Pro Logic® II. The delivery format and the speaker configuration are independent, and it is the decoder's job to bridge them effectively.

A perceptual coding system for audio , developed by Dolby Laboratories and accepted as an international standard. Dolby Digital is the most common means of encoding audio for DVD-Video and is the mandatory audio compression system for 525/60 (NTSC) discs.

Referred to a Digital Video Disc, and then later as Digital Versatile Disc, the DVD forum then pronounced it as a noun, si it does not stand for anything anymore. It is a a specification for a family of products for storing video/audio and date on 8 cm and 12 cm optical discs.

The differences between the loudest and softest sound in an audio signal. The dynamic range of digital audio is determined by the sample size. Increasing the sample size does not allow louder sounds; it increases the resolution of the signal, thus allowing softer sounds to be separated from the noise floor (and allowing more amplification with less distortion). Therefore the dynamic range refers to the difference between the maximum level of distortion-free signal and the minimum limit reproducible by the equipment.

To transform data for storage or transmission, usually in such a way that redundancies are eliminated or complexity is reduced. Most compression is based upon one or mode encoding methods. Data such as audio or video is encoded for efficient storage and is decoded for access or display.

Frames per second. A measure of the rate at which pictures are shown to create a motion video image. In NTSC and PAL video, each frame is made up of two interlaced fields.

The international standard specifying the format of Digital component Video.

Dolby Digital carries additional information (metadata) that is input during encoding to control audio parameters in a consumer decoder.

Motion Pictures Expert Group. An international committee that developed the MPEG family of audio and video compression systems.

Audio compressed according tho the MPEG perceptual encoding system. MPEG-1 audio provides two channels, which can be in Dolby surround format. MPEG-2 audio adds data to provide discrete multichannel audio. Stereo MPEG audio is one of the two mandatory audio compression systems for 625/50 (PAL) DVD-Video.

video compressed according to the MPEG encoding system. MPEG-1 is typically used for low data rate video such as VideoCD. MPEG-2 is used for higher quality video, especially interlaced videos, such as DVD or HDTV. It is encoded in accordance with the ISO/IEC 13818 specification.

National Television Systems Committee. A committee organised by the Electronics Association (EIA) that developed commercial television broadcast standards for the U.S. The group first established black and white TV standards in 1941, using a scanning system of 525 lines at 60 fields pre second. The second committee standardised colour enhancements using 525 lines at 59.94 fields per second. NTSC refers to the composite colour-encoding systems. The 525/59.94 scanning system (with a 3.58 MHz colour subcarrier) is identified by the letter M and is often incorrectly referred to as NTSC. The NTSC standard is facetiously referred to as meaning never the same colour twice, because of the system’s difficulty in maintaining a colour system.

Phase alternate line. A video standard used in Australia and Europe and other parts of the world for composite colour encoding. Various versions of PAL use different scanning systems and colour sub carrier frequencies (identified with the letters B,D,G,H,I,M, and N) the most common being 625 lines at 50 fields per second, with a colour sub carrier of 4.43 MHz. PAL is also said to mean perfect at last.

Pulse Code Modulation. An uncompressed, digitally coded representation of an analog signal. The waveform is sampled at regular intervals and series of pulses in coded form (usually quantised) are generated to represent the amplitude.

TBA

The smallest picture element of an image (one sample of each colour component) A single dot of the array of dots that make up a picture. Sometimes abbreviated to pel. The resolution of a digital display is typically specified in terms of pixels (width by height) and colour depth (the number of bits required to represent each pixel)

A digital video software standard developed by Apple Computer for Macintosh (Mac OS) and Windows operating standards. QuickTime is used to support audio and video playback from a DVD.

A continuous flow of data, usually digitally encoded, designed to be processed sequentially. Also called a bitstream.

A video signal (or component of a video signal) containing information necessary to synchronise the picture horizontally and vertically. Also, specially formulated data on disc, which helps the readout system identify location and specific data structures.

Data that can read and processed at a volume that varies over time. A data compression technique that produces a data stream between a fixed minimum and maximum rate. A constant level of compression is generally maintained, with the required band width increasing or decreasing depending on the complexity of the data being encoded. This produces a better quality picture, but can consume more disc storage.

A video image wider that a standard 1.33 (4:3) aspect ratio. When referring to DVD or HDTV, widescreen usually indicates a 1.78 (16:9) aspect ratio.