Analog television
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Analog television (or analogue television) encodes television picture and sound information as an analog signal, that is, by varying the amplitude and/or frequencies of the signal. All systems preceding digital television can be considered analog.
An analog television picture is drawn on the screen an entire frame each time, in the manner of a motion picture (cinematograph) film, irrespective of the picture content. Using NTSC, PAL or SECAM analog encoding and modulating onto a VHF or UHF carrier is a highly effective way of distributing an analog television picture, whereas attempting to distribute the same content in a native uncompressed digital form (as Digital Audio Compact Disc 'CD' is) would require an approx 250 G bit/s data rate, which is many times in excess of the bandwidth taken by a standard analog UHF channel.
Because there is no bandwidth compression whatsoever in analog TV, it is often a belief there are signals transmitted that are considered as carrying no useful information. However, this is partly incorrect, it has been found for example that when viewing an analog transmission, subject movement appears always to be 'natural and flowing' at all times, with a total absence of the 'jerky' unnatural movement effects seen with present-day digital TV technology (most apparent on slowly-moving subjects). This is because with analog TV there is no mechanism deciding what constitutes a 'moving object' from its 'background' and how to display movement. Each frame is refreshed in its entirety from the original source, as in the case of a motion picture cine film.
Analog television does not suffer from certain picture defects seen on present-day digital television, examples are:
- Paint-By-Numbers color effects. (i.e. light obliquely falling onto a surface should appear smoothly-graduated, but instead appears as a series of bands, this is Quantisation Distortion due to reduced sample depth).
- Poor Lip Sync. (Because analogue TV receives and outputs sound and video simultaneously without decompression and error correction, sync. can never be wrong).
- StoneWall loss of reception. (Analog TV will degrade in proportion to the reduction in signal strength, however digital TV allows a significant drop in the signal strength before the picture is affected, whereupon it will completely freeze or 'block out').
American television stations are scheduled to switch to digital output by February 2009. [1]
Australian and UK Analogue TV is to be switched off between 2008 and 2012. [2]
Common analog television systems:
