Disc‐Based Audio‐Video Technology
| Published date | 01 July 2006 |
| DOI | https://doi.org/10.1108/07419050610692307 |
| Pages | 27-33 |
| Date | 01 July 2006 |
| Author | Scott Piepenburg |
| Subject Matter | Library & information science |
Disc-Based Audio-Video Technology
Scott Piepenburg
LIBRARY HITECH NEWS Number 6 2006, pp. 27-33, #Emerald Group Publishing Limited, 0741-9058, DOI 10.1108/07419050610692307 27
Ever since Edison uttered the words
``Mary had a little lamb'' science and
marketing people have been looking for
the ``perfect'' disc storage medium for
sound, and then later video. There are
three hurdles that every format has to
address:
(1) Accurate. The information stored
should be a faithful representation
of the original source, with as little
distortion as possible, or at least
less than can be discerned by the
user.
(2) Compact. Is the carrier of a size
that users will find it portable and
easy to take with them. Particularly
important for ``on the go'' applica-
tions and users.
(3) Efficient. Is the medium able to be
manufactured, marketed, and dis-
tributed in a profitable manner. It
can also be defined as the medium
making the best possible use of the
available storage space.
These three variables exist on a
triangle. It is possible to have any two
of these variables in a given format, but
not all three. A format can yield
accurate signal reproduction and be
conveniently sized, but it will not
utilize an ``efficient'' storage
technology. It can use an efficient
storage technology and be compact, but
signal accuracy will suffer. To a
marketing person, cost-effective may
be substituted for efficient since it
comes down to the fact if a format can
be made acceptable to a great enough
mass of people, it will be successful and
will make money.
This paper seeks to be a short
overview of some of the technologies
that have been used or are currently
being used. It is not intended to be
comprehensive and the writer assumes
a basic understanding of sound and
video terminology. A short glossary is
included at the end for convenience.
Each format is evaluated using four
criteria: technique, encoding, complete-
ness, and distribution.
Technique describes how the signal
is recorded. It is a single continuous
signal, similar to a sine wave, or is the
recorded signal broken into a large
number of smaller, discrete sections. It
is important to remember that even
thought it may seem that a linear or
continuous signal is inherently better, a
discrete signal can seem to be just as
good. If you remember the playing card
that you put on your bike between the
spokes, if you spun the wheel fast
enough, it sounded like a continuous
tone. The same would be true of a
circular saw; each tooth makes a
discrete cut, but because they are so
close together and our ears do not have
the sensitivity to discriminate between
each impact, the sound seems
continuous. Think of an incandescent
light bulb; it turns ``on and off'' sixty
times per second because of alternating
current, yet it appears to be on all the
time. If you ``chop up'' a sine wave or
signal into enough small portions, it
actually appears to be continuous.
Encoding defines how we store the
signal. Do we use some type of
modulation or physical variation, or do
we convert the signal to a numerical
string of bits and store it. An analog
signal has the benefit of being more
consistent from one moment to the next,
but suffers from the physics of wear and
tear as well as the dynamics of the
movement of the recording/playback
instrument. Digital signals have the
benefit of being able to be stored and
reproduced an infinite number of times
without decay, but require significant
amounts of storage space and if not
enough ``power'' is devoted to the
conversion medium, can result in a
degradation of final signal quality.
Completeness is exactly that. How
much of the original source signal is
recorded. Some formats intentionally
``discard'' parts of a signal that are
determined to be unnecessary. The
human ear and eye are easily fooled and
suffer many limitations, such as not
being able to discern low notes very
well. Various recording schemes
depend on this so that less signal needs
to be recorded, thereby resulting in a
reduction of needed storage space.
Distribution means how widely was
the format accepted and distributed
among the general public. Some
formats find a niche market, while
others are embraced by the general
population. The more widely accepted
formats typically have a lower cost due
to lower fixed costs and greater market
base to spread out those costs over. It
also results in a greater ubiquity of
content, provided the customer bases is
willing to pay for it and embrace the
format and the content costs.
Compression vs reduction also needs
to be considered. The two terms are not
interchangeable. Compression means
that the original signal has been reduced
in size for storage but either contains all
the original information or can be used
to reconstruct a duplicate of the original
signal. Reduction is a methodology that
is used to minimize the amount of
information that has to be stored.
Typically, it is not possible to re-create
an exact duplicate of the original
information.
The following are some of the
technologies that have been used or are
currently being used.
Record albums
.Technique: linear.
.Completeness: full.
.Encoding: analog.
.Distribution: wide.
Record albums encompass a large
area. The most common is the 12in
``LP'' or long playing format developed
by Columbia Music and adopted as the
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