DVD Demystified

DVD Technology Primer
thing. If the receiver reclocks the signal, you can use the world’s cheapest
transport and get better quality than with an outrageously expensive, vacuum-sealed,
hydraulically cushioned transport with a titanium-lead chassis.
The reason better transports produce perceptibly better results is that
most receivers do not reclock or otherwise sufficiently attenuate interface
jitter. Even digital receivers with DSP circuitry usually operate directly on
the bit stream without reclocking it.
Interface jitter affects all digital signals coming from a DVD player: PCM
audio, Dolby Digital, DTS, MPEG-2 audio, and so on. In order to stay in sync
with the video, the receiver must lock the decoder to the clock in the incoming
signal. Since the receiver depends on the timing information recovered
from the incoming digital audio signal, it is susceptible to timing jitter.
There is an ongoing tug of war between engineers and critical listeners.
The engineers claim to have produced a jitterless system, but golden ears
hear a difference. After enough tests, the engineers discover that jitter is
getting through somewhere or being added somewhere, and they go back to
the drawing board. Eventually, the engineers will win the game. Until then,
it is important to recognize that most sources of jitter have little or no perceptible
effect on the audio or video.
Pegs and Holes: Understanding
Aspect Ratios
115
The standard television picture is restricted to a specific shape: a third
again wider than it is high. This aspect ratio is designated as 4:3, or 4 units
wide by 3 units high, also expressed as 1.33. 16 This rectangular shape is a
fundamental part of the NTSC and PAL television systems—it cannot be
changed without redefining the standards. 17
16There is no special meaning to the numbers 4 and 3. They are simply the smallest whole numbers
that can be used to represent the ratio of width to height. An aspect ratio of 12:9 is the same
as 4:3. This also can be normalized to a height of 1, but the width becomes the repeating fraction
1.33333...,which is why the 4:3 notation is generally used. For comparison purposes, it is useful
to use the normalized format of 1.33:1 or 1.33 for short.
17The next generation of television—known as HDTV, ATV, DTV, etc.—has a 1.78 (16:9) picture
that is much wider than current television. However, the new digital format is incompatible with
existing standard recording and display equipment.