Technical information

Bit The smallest unit of digital information. A single bit can carry just one of two
values: 0 or 1. There are eight bits in a byte, 1,024 bytes in a kilobyte, 1,024
kilobytes in a megabyte, 1,024 megabytes in a gigabyte and 1,024 megabytes in
a terrabyte. Sometimes, though, the traditional 1,000 is used rather than
1,024, leading to confusion. A bit should generally be abbreviated as lower-case
'b' (compared to 'B' for byte). Thus 128kb/s means 128 kilobits per second,
whereas 128kB means 128 kilobytes.
Bit depth The size of the number that records each digital sample. Since the
system is digital, the number relates to powers of two. The compact disc uses a
bit depth of 16, which allows 65,536 different levels to be used to track the
analogue source signal. DVDs usually also use 16, but may also use 20 bits
(which gives over a million levels) or 24 bits (which gives more than 16.7 million
levels). The greater the bit depth, the lower the harmonic distortion and
quantization noise, and the more storage space required for the signal. Audio
recording studios use 20bit and 24bit, which is reduced down to16 bit for
compact disc. Specialist audio companies are now offering 20 or 24 bit audio for
download, this offers super audio CD quality and above.
Bit rate The number of digital bits a system transfers per second. In general, the
higher the bit rate, the higher the quality of the signal. In every case, the higher
the bit rate, the more data space required. With audio bit rates are measured in
the hundreds of kilobits per second (kb/s). With DVD video, they are measured in
megabits per second (mb/s).
Bitstream The digital audio output of a DVD player, when switched to outputting
the DVD's native digital audio format. Most DVD players can be switched to
output a Dolby Digital bitstream, or convert the digital output to PCM.
Blu-ray A high capacity development of the DVD which uses higher frequency
(blue) rather than red light frequencies for reading the disc. The combination of
shorter wavelengths and other enhancements bumps up the maximum capacity
from 8.5GB for a dual layer DVD to around 27GB, allowing the storage of high
definition video.
Byte Eight bits. A byte can represent numbers between 0 and 255, or when
interpreted as signed integers, between -128 and +127.
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