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AAC: Advanced Audio Coding, a lossy compression format regarded to have better sound quality than MP3 at the lower bitrates. AAC files use MPEG-4 audio compression and is the format most commonly used with iPods and Apple’s iTunes Music Store. It is used in the Nintendo Wii and in video applications, as well. See Bitrate, Lossy Compression, MPEG-4.
AACS: Advanced Access Control System, a layer of digital rights managament (DRM) used on Blu-ray Discs and HD DVDs. See DRM.
AC-3: See Dolby Digital.
Acoustic Suspension: A loudspeaker using a sealed enclosure, rather than a ported one. Acoustic suspension speakers are favored for their tight, precise sound and accurate, low distortion bass reproduction, but they typically require more power and do not produce as much bass as ported designs. The first acoustic suspension speaker, the Acoustic Research AR-1, was introduced in 1956 by Edgar Villchur and Henry Kloss and is considered a landmark audio achievement. See Ported Speaker.
Adaptall, Adaptall 2: Interchangeable lens mount system used by Tamron for their SLR lenses. Adaptall mounts allowed a single lens to be used on camera bodies from many manufacturers simply by changing to the proper mount. The Adaptall 2 system used a bayonet mount and was much more refined than the original Adaptall system. Adaptall 2 lenses allowed users of uncommon cameras such as Prakticas, Rollei 35mm SLRs, etc. have access to a wide range of good-quality lenses at affordable prices. See T-Mount. Learn more off site
Additive Primary Colors: Red, Green and Blue. White light is composed of equal amounts of red, green and blue light. Two examples of the use of the additive primary colors in electronics is in projection TVs with a red, green and blue CRT or in camcorders with a red, green, and blue chip. Additive primaries Each additive color has an opposite subtractive color: Red-Cyan, Each subtractive color has an opposite additive color: Yellow-Blue, Each subtractive color has an opposite additive color: Red-Cyan, Green-Magenta, Blue-Yellow. See Subtractive Primary Colors.
AEL: Auto Exposure Lock. Auto exposure lock is a camera function that locks the exposure setting so composition can be changed before the picture is taken. It is useful in situations such as heavily backlit subjects. This is achieved by locking the exposure with the camera close to the subject, then backing up, composing and then taking the picture.
AM: Amplitude Modulation, the system used for AM radio broadcasts. AM Radio has very long range (especially at night when signals bounce off the ionosphere) but less clarity than FM broadcasts.
Amplifier: The amplifier forms an electronic circuit with the speakers and drives (powers) them.
Anamorphic: Motion picture lenses that squeeze a widescreen image on to a regular 35mm frame of film. An anamorphic projection lens corrects the image when it is projected on the screen.
Antenna, Directional: Directional antennas must be pointed in the direction of the broadcast towers to tune a signal. These are the most effective at tuning a signal, but require a rotor (rooftop antenna) to turn the antenna, or it must be turned manually if it is a set-top directional antenna.
Antenna, Omnidirectional: Omnidirectional antennas can receive signals from 360 degrees without being rotated. They are not as effective as directional antennas but may be all that is needed in areas with good reception.
Anti-Skate: Anti-skate is force applied to a tonearm (usually by using a weight) to keep it from “skating” across the record. See Tonearm.
AOD: Advanced Optical Disc, name given to HD DVD during its development phase. See HD DVD.
Aperture: The opening of a camera lens, aperture is variable and controlled by a diaphragm. The smaller the number, the wider the aperture and the more light is passed through. See f-Stop.
Aperture Priority: An automatic exposure mode where the user chooses the aperture and the camera selects the proper shutter speed based on lighting conditions. Aperture priority is useful to determine depth of field. By selecting a low number, there is low depth of field, a higher number, more depth of field. See Depth of Field.
APO: See Apochromatic Lens.
Apochromatic Lens: A photographic lens exhibiting an extremely high level of color correction. Most apochromatic lenses are telephoto designs because telephoto lenses are more likely to have problems focusing all the different wavelengths of light on the same plane, hence needing more correction. Most apochromatic lenses use LD glass elements. See LD.
Apple Lossless Compression: A lossless compression scheme used by Apple’s iTunes program. It reduces the size of a CD’s audio files by 50% with no loss in audio quailty. See Lossless Compression.
Aspect Ratio: The proportions of an image, such as 4:3 and 16:9.
Aspherical: A lens element having a non-sphercial shape. Aspheric lens elements are harder to manufacture than spherical elements, but provide superior performance in many kinds of lenses.
ATSC: Advanced Television Systems Committee. Group responsible for the new digital television standards. See DTV.
Audible Range of Frequencies: See 20-20,000 Hz.
AUTO Mode: Mode on digital cameras where all user settings are overridden (including setting ISO) and the camera operates purely as a point-and-shoot. See ISO.
Averaging Meter: A light meter that averages all the light in a scene. See also 18% Gray, Light Meter.
Artifacts: Undesirable, artificial defects in a digital image, usually caused by compression or poor image processing.
AVC: Advanced Video Coding, a version of MPEG-4 used on Blu-ray Discs, HD DVDs, satellite TV broadcasts, and streaming web video. See MPEG-4.
AVCHD: High definition camcorder format. AVCHD camcorders record AVC video to an internal hard drive. Because of high compression, video quality tends to be inferior to HDV camcorders, though it uses a more advanced video compression standard. See AVC, Lossy Compression, HDV.
Audyssey: Designer and manufacturer of room correction and other audio signal processing technology. See Room Correction. Learn more off site
