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Audio equipment, Broadcast Equipment, Video Equipment
Audio equipment
A piece of audio equipment is any device designed principally to reproduce, record or process sound. This includes microphones, radio receivers, AV receivers, CD players, tape recorders, amplifiers, mixing consoles, effects units and loudspeakers.
Sound recording and reproduction is an electrical or mechanical inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording. Acoustic analog recording is achieved by a small microphone diaphragm that can detect changes in atmospheric pressure (acoustic sound waves) and record them as a graphic representation of the sound waves on a medium such as a phonograph (in which a stylus senses grooves on a record). In magnetic tape recording, the sound waves vibrate the microphone diaphragm and are converted into a varying electric current, which is then converted to a varying magnetic field by an electromagnet, which makes a representation of the sound as magnetized areas on a plastic tape with a magnetic coating on it. Analog sound reproduction is the reverse process, with a bigger loudspeaker diaphragm causing changes to atmospheric pressure to form acoustic sound waves. Electronically generated sound waves may also be recorded directly from devices such as an electric guitar pickup or a synthesizer, without the use of acoustics in the recording process other than the need for musicians to hear how well they are playing during recording sessions.
Broadcast Equipment
Forms of electronic broadcasting Historically, there have been several different types of electronic broadcasting media: Telephone broadcasting: the earliest form of electronic broadcasting.
Telephone broadcasting began with the advent of Théâtrophone systems, which were telephone-based distribution systems allowing subscribers to listen to live opera and theatre performances over telephone lines, created by French inventor Clément Ader in 1881. Telephone broadcasting also grew to include telephone newspaper services for news and entertainment programming which were introduced in the 1890s, primarily located in large European cities. These telephone-based subscription services were the first examples of electrical/electronic broadcasting and offered a wide variety of programming .
Radio broadcasting : radio broadcasting is an audio (sound) broadcasting service, broadcast through the air as radio waves from a transmitter to an antenna and, thus, to a receiving device. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both.
Television broadcasting (telecast), experimentally from 1925, commercially from the 1930s: this video-programming medium was long-awaited by the general public and rapidly rose to compete with its older radio-broadcasting sibling. Cable radio (also called "cable FM", from 1928) and cable television (from 1932): both via coaxial cable, serving principally as transmission mediums for programming produced at either radio or television stations, with limited production of cable-dedicated programming. Satellite television (from circa 1974) and satellite radio (from circa 1990): meant for direct-to-home broadcast programming (as opposed to studio network uplinks and downlinks), provides a mix of traditional radio or television broadcast programming, or both, with satellite-dedicated programming. Webcasting of video/television (from circa 1993) and audio/radio (from circa 1994) streams: offers a mix of traditional radio and television station broadcast programming with internet-dedicated webcast programming.
Characteristics of video streams
Number of frames per second Frame rate, the number of still pictures per unit of time of video, ranges from six or eight frames per second (frame/s) for old mechanical cameras to 120 or more frames per second for new professional cameras. PAL (Europe, Asia, Australia, etc.) and SECAM (France, Russia, parts of Africa etc.) standards specify 25 frame/s, while NTSC (USA, Canada, Japan, etc.) specifies 29.97 frame/s. Film is shot at the slower frame rate of 24photograms/s, which complicates slightly the process of transferring a cinematic motion picture to video. The minimum frame rate to achieve the illusion of a moving image is about fifteen frames per second.
Interlacing Video can be interlaced or progressive. Interlacing was invented as a way to achieve good visual quality within the limitations of a narrow bandwidth. The horizontal scan lines of each interlaced frame are numbered consecutively and partitioned into two fields: the odd field (upper field) consisting of the odd-numbered lines and the even field (lower field) consisting of the even-numbered lines. NTSC, PAL and SECAM are interlaced formats. Abbreviated video resolution specifications often include an i to indicate interlacing. For example, PAL video format is often specified as 576i50, where 576 indicates the vertical line resolution, i indicates interlacing, and 50 indicates 50 fields (half-frames) per second. In progressive scan systems, each refresh period updates all of the scan lines. The result is a higher spatial resolution and a lack of various artifacts that can make parts of a stationary picture appear to be moving or flashing. A procedure known as deinterlacing can be used for converting an interlaced stream, such as analog, DVD, or satellite, to be processed by progressive scan devices, such as TFT TV-sets, projectors, and plasma panels. Deinterlacing cannot, however, produce a video quality that is equivalent to true progressive scan source material.
Display resolution Common computer and TV display resolutions. The size of a video image is measured in pixels for digital video, or horizontal scan lines and vertical lines of resolution for analog video. In the digital domain (e.g. DVD) standard-definition television (SDTV) is specified as 720/704/640×480i60 for NTSC and 768/720×576i50 for PAL or SECAM resolution. However in the analog domain, the number of visible scanlines remains constant (486 NTSC/576 PAL) while the horizontal measurement varies with the quality of the signal: approximately 320 pixels per scanline for VCR quality, 400 pixels for TV broadcasts, and 720 pixels for DVD sources. Aspect ratio is preserved because of non-square "pixels". New high-definition televisions (HDTV) are capable of resolutions up to 1920×1080p60, i.e. 1920 pixels per scan line by 1080 scan lines, progressive, at 60 frames per second. Video resolution for 3D-video is measured in voxels (volume picture element, representing a value in three dimensional space). For example 512×512×512 voxels resolution, now used for simple 3D-video, can be displayed even on some PDAs.