AV/IT Glossary—27 Days of #AVabc—H


HDR—High-dynamic-range imaging (HDRI or HDR) is a technique used in imaging and photography to reproduce a greater dynamic range of luminosity than is possible with standard digital imaging or photographic techniques.


H.264 (MPEG-4 AVC)—Block-oriented motion-compensation-based codec standard developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG). It is the product of a partnership effort known as the Joint Video Team (JVT). H.264 is used in such applications as Blu-ray Disc, videos from YouTube and the iTunes Store, DVB broadcast, direct-broadcast satellite television service, cable television services, and real-time videoconferencing.

H.264 Encoding—A standard for video compression equivalent to MPEG-4 Part 10 or MPEG-4 AVC – Advanced Video Coding. H.264 was created to provide video quality suitable for high definition applications at bit rates lower than that utilized in MPEG-2, the compression standard used in DVD authoring.

H.320—ITU-T H.320 is a family of standards developed for video teleconferencing systems using ISDN. It references H.261 (for video); G.711, G.722, and G.728 (for audio); H.221, H.230, H.231, H.233, H.234, H.242, and H.243 (for control). The standard allows a system from one manufacturer to talk to a system from another manufacturer, just as two different brands of FAX machines can talk to each other.

H.323—ITU standard allowing audio, video, and data to be transmitted by way of the Internet Protocol (LAN/WAN). It is the umbrella standard defining multiple codes, call control, and channel setup specifications. Basically, videoconferencing over IP.

Half Duplex—Data or audio transmission that can occur in two directions over a single line, but only one direction at a time.

Halogen-Free (LSFOH)—Low Smoke and Fumes Zero Halogen. Refers to the material used in cable insulation that emits reduced amounts of hazardous smoke and toxic fumes in the event of a fire. Certain countries, such as in the UK, may require LSFOH cable insulation.

Handshake/Handshaking—Handshaking is an automated process of negotiation that dynamically sets parameters of a communications channel established between two entities before normal communication over the channel begins. In communications, the moment when the transmitting and receiving devices identify themselves to each other. It follows the physical establishment of the channel and precedes normal information transfer.

Hard Disk—A mass storage media for digital information used in computers, video and audio and recently also used for digital image/video storage in digital cameras and camcorders. In contrast to a floppy disk*, the hard disk is usually non-removable (though there are already some removable and transportable hard disks). The access time of a Hard disk is much shorter than that of a floppy disk, and the amount of data (images or full video-scenes, for example) that can be stored on a large disk can reach several gigabytes (thousands of megabytes). The name hard disk comes from its internal construction of metal (mainly aluminum) platters, which are very stiff, and not floppy.

Harmonics (in music: overtones)—Multiples of an original frequency that add to and modify the original frequency. A pure sine wave is free of harmonics. When harmonics occur in electronic signals, it adds distortion to the original signal, causing undesirable results.

HAVi (Home Audio/Video interoperability)—A FireWirebased technology for controlling various components of a home-theater system as a single unit with one remote control. This “interoperability” is possible because the FireWire interface carries control data along with digital audio and video in the same cable.

HDBaseT—HDBaseT, promoted and advanced by the HDBaseT Alliance, is a consumer electronic (CE) and commercial connectivity standard for transmission of uncompressed high-definition video (HD), audio, power, home networking, Ethernet, USB, and some control signals, over a common category (Cat5e or above) cable with a standard connector (8P8C, often "RJ45").

HD Connector—A high-density D connector having its pins arranged close together, sometimes in three rows instead of two rows. Example: a 15-pin VGA connector (HD) vs. a Mac connector (D).

HDCP-High-bandwidth Digital Content Protection—A digital rights management scheme developed by Intel to prevent the copying of digital video and audio content. HDCP is mandatory for the HDMI interface, optional for DVI. HDCP defines three basic system components: source, sink, and repeater.

Sources send content to the display. Sources can be set-top boxes, Blu-ray Disc players, computer-graphics cards, and so forth. A source can have only one HDCP transmitter.

Sinks decrypt the content so it can be viewed. Sink is typically used to describe a flat panel display, television, or projector. Sinks can have one or more HDCP receivers.

Repeaters sit between Sources and Sinks. They accept content, decrypt it, then re-encrypt and transmit. Internally, a Repeater may provide signal processing, such as scaling, splitting out audio for use in an analog audio playback system, or splitting the input data stream for simultaneous viewing on multiple displays. Switchers, matrix switchers, and distribution amplifiers are all examples of Repeaters.

HD DVD—New optical disc format that can store 30BGB on a dual-layer disc the size of a DVD. Competing with Blu-ray Disc to be the high-definition replacement for DVD.

HDMI-High-Definition Multimedia Interface—The first industry-supported uncompressed, all-digital audio/video interface. It's a single cable and user-friendly connector that replaces the maze of cabling behind the home entertainment center. HDMI provides an interface between any audio/video source, such as a set-top box, DVD player, or A/V receiver and an audio and/or video monitor, such as a digital television (DTV), over a single cable. HDMI supports standard, enhanced, or high-definition video, plus multi-channel digital audio on a single cable. It transmits all ATSC HDTV standards and supports 8-channel digital audio with bandwidth to spare to accommodate future enhancements and requirements.

HD-SDI—The high-definition version of SDI specified in SMPTE-292M. This signal standard transmits audio and video with 10 bit depth and 4:2:2 color quantization over a single coaxial cable with a data rate of 1.485 Gbit/second. Multiple video resolutions exist including progressive 1280x720 and interlaced 1920x1080 resolution. Up to 32 audio signals are carried in the ancillary data.

HDTV-High Definition Television—HDTV refers to a complete product/system with the following minimum performance attributes: a receiver that receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher; aspect ratio capabilities for displaying a 16:9 image; receives and reproduces, and/or outputs Dolby Digital audio.

Headend—A control center in a cable television system where various signals are brought together and monitored before being introduced into the cable network.

Headroom—The difference in dB SPL between peak and average level performance of an audio system. For a speech-only system, this value is 10 dB.

Heat Sink—A device that absorbs and dissipates heat produced by an electrical component.

Helical Scan—A method of recording video information on VCR tapes. The tape is scanned in a helical (slanted) way rather than horizontally or vertically. The helical scan method packs much more information on a given length of magnetic tape than all other methods. For this reason this method is used in the digital world as well - in DAT* and in digital video recording systems.

Hemispheric Polar Pattern—The dome shape of the region that some microphones will be most sensitive to sound. Used for boundary microphones.

Hertz (Hz)—A unit of frequency; describing the number cycles per second. 1Hz = 1 cycle/second…1MHz = 1 Million cycles/second

High-Density Layer—The information layer in a Super Audio CD that contains high-resolution digital audio. high-pass filter A circuit that allows high frequencies to pass, but blocks low frequencies. Also called a “lowcut filter.” High-pass filters are often found in A/V receivers and A/V controllers to keep bass out of the main speakers when using a subwoofer.

Hi-8—A Y/C video format similar to Super-VHS, introduced by SONY™, using 8mm wide videotapes. Picture quality is very high and camcorders using this format are very small and handy, making them a very good choice for amateur and semi-pro video photographers.

Hi-Color—A computer graphics format, beyond VGA* and Super-VGA*, which displays 32,000 or 64,000 simultaneous colors on the screen at 640x480 pixels resolution and above. This number of shades of color, simultaneously displayed on the screen, exceeds the color resolution of the human eye, which can resolve about 4,000 different shades of color. True color displays 16.7 million shades of color (24-bit color information).

High Fidelity—Hi fi, accurate, and faithful reproduction of the original. Absence of distortion or enhancements.

High Impedance—Hi Z or high Z. A relative term that is different for each application. In video, when the signal is not terminated it has a Hi Z load. Hi Z is typically 800 to 10k ohms or greater.

High Pass Filter—A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass. Also called a “low cut filter.”

High-Definition Video—Refers to any video system of higher resolution than standarddefinition (SD) video, and most commonly involves display resolutions of 1280×720 pixels (720p) or 1920×1080 pixels (1080i/1080p).

High-Resolution Digital Audio—Generally regarded as digital audio with a sampling rate greater than 48kHz and a word length longer than 16 bits.

Hiss—Broadband higher-frequency noise typically associated with poor audio system gain structure.

Home Automation—Home automation is the use and control of home appliances remotely or automatically.

Home Theater—The combination of high-quality audio and video in your home.

Home THX—A set of patents, technologies, and playback standards for reproducing film soundtracks in the home as the producer intended. THX doesn’t compete with surround formats such as Dolby Pro Logic or Dolby Digital, but instead builds on them.

Hop—In a packet-switching network, a hop is the trip a data packet takes from one router or intermediate point to another in the network.

Hop Count—On the Internet (or a network that uses TCP/IP), the number of hops a packet has taken toward its destination.

Horizontal Blanking—After making a scan line (left-to-right), the electron beam in a CRT retraces (returns) to the left side of the screen to begin the next line. During retrace time, it is not putting picture information on the screen, so the beam is turned off, or blanked. About 83% of each horizontal cycle is spent writing the line, while 17% is spent retracing the beam to the left before starting the next line.

Horizontal Blanking Interval—The time during which the electron beam is turned off so that it can move into position to begin the next scan line; usually a very brief period, lasting between 5 -15 microseconds.

Horizontal Cabling—Telecommunications cabling used to cover a floor area. It extends from the horizontal cross-connect in the telecommunications room to a local access outlet.

Horizontal Centering Control—Adjusting the horizontal centering control shifts the displayed image left or right on the display screen. Also called “horizontal shift.”

Horizontal Cross-Connect-HC—A patch panel or LAN-Local Area Network panel, used to cross-connect horizontal cables to other cabling within a building or facility.

Horizontal Double Images—A video problem when the display is split down the middle with two identical but squeezed images displayed on each side of the screen.

Horizontal Filtering—In some Extron scan converters and other products, this is a feature that controls the sampling of the horizontal plane, thereby affecting the sharpness or smoothness of the scan-converted picture.

Horizontal Rate—Horizontal scanning frequency. The number of complete horizontal lines (trace and retrace) scanned per second. Measured in kHz, the NTSC standard is 15.75 kHz.

Horizontal Resolution—The number of vertical lines that can be perceived in a video device.

Horizontal Sync—The pulses that control the horizontal scanning of the electron beam in a video device. On connector panels, “H” identifies the connector for horizontal sync, and “H/HV” means it is also used for combined or “composite” horizontal and vertical sync (RGBS).

Horizontal and Vertical Sync Pulses—The horizontal sync* signal is a short pulse at the beginning of each video line which keeps the horizontal scanning of the monitor exactly in step with the transmission of each new line. The vertical sync signal is a pulse transmitted at the beginning of each field and frame. Its purpose is to maintain the monitor in field-by-field synchronization with transmission of the next frame pulse. Sync signals reside in a part of the video signal in which no visual picture information is transmitted. During that particular part of the transmission (the blanking retrace period* or vertical interval*), the electronic beam is blanked and retraces back to the other side of the screen to start a new line or a new frame. Both horizontal and vertical sync are needed to create a fully stable picture.

Horizontal Tilt—A line-time distortion, tilting the edge of a white bar. The phenomenon shows on the screen as white or black streaks, bleeding away from the original position, creating a muddy, fuzzy image on the screen. It is a result of the poor low frequency response of an amplifier, (see Vertical tilt.) Horizontal Tilt should not be greater than 0.5% in professional applications.

Horns—Loudspeakers that reproduce mid to high frequencies.

Hot Plug/Hot Plug Detect—Describes a feature of DVI, HDMI, USB, and other digital technologies which allows a host device, such as a computer, to detect the presence of a new device without intervention by the user. Hot Plug technology allows a new device to be added to a system while it’s still connected to a power source. Once the new device is connected, the Hot Plug Detect circuit, or HPD, senses the new device and tells the rest of the system that the device is ready to either send or receive a data stream.

Hot Spot—Commonly seen on high-gain screens and screens designed for slide or movie projection, a hot spot is a circular area where the image is brighter than the rest of the screen. The hot spot is always located along the line of sight, and “moves” with the line of sight.

Hot-Swap—The ability to change electronic components, such as circuit boards or peripheral devices, without removing power from the device.

HSIHue, Saturation and Intensity. This is a color space* (a way to represent color) that describes an image. This measure uses polar coordinates. RGB color space is based on a Cartesian coordinate system.

HSL—Hue, Saturation and Lightness. A measure similar to HSI.

HSV—Hue, Saturation and Value. A measure similar to HSI.

HTML—Hypertext Markup Language. A formatting computer language used to create web pages.

HTTP—HyperText Transfer Protocol. A Web protocol based on TCP/IP that is used to retrieve hypertext objects from remote Web pages.

Hub—A shared transmission media to which devices on a network are interfaced. Ethernet hubs have mostly given way to Ethernet switches.

Hue—(1) Color value or saturation, as opposed to brightness or intensity. (2) Tint control – Hue is the parameter of color that allows us to distinguish between colors. The hue, or tint control, adjusts the amount of color displayed.

Huffman Coding—A method of entropy encoding used in lossless data compression where the most frequently occurring values use the shortest codes.

Hum—The coupling of an unwanted frequency into other electrical signals. In audio, hum can be heard; in video, it can appear as waves or bars in the picture. Often it is an audible disturbance caused by the power supply, or an improper ground.

Hum Bar(s)—Interference in the form of a horizontal bar moving vertically on the display screen. Hum bars can be caused by ground loops

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