V: Colour difference signal used in PAL. (R—Y) reduced in amplitude and bandwidth limited to about 1.2 MHz. V = 0.877 (R—Y).
vacuum tube: An evacuated glass envelope containing several metal electrodes. It was invented first as a diode by Sir John Ambrose Fleming. See also thermionic valve.
valve: See thermionic valve.
valve rollers: See fire rollers.
variable area track: A photographic sound track in which the image width varies according to the sound modulation.
variable bit rate (VBR): (1) Networked data that is tolerant of delays and changes in its allocated data rate. It is an ATM service class that uses statistical multiplexing. See also available bit rate (ABR), current bit rate (CBR) and uncommitted bit rate (UBR).(2) In video and audio ...