First, let's put some contrasting definitions in place to establish terms of reference. When we call something an analogue medium, we are referring to the fact that there is a continuous physical relationship between the original message and its reproduction. Speech and writing are represented by print in a book; musical sounds are represented by grooves in an LP or magnetized iron particles on an audio tape; light bouncing off an object is focused by a camera lens to change the colours of chemicals on film. There is often a one-to-one correspondance between the signal and its translation into a physical medium, or reproduction. Analogue and analogous both derive from the Greek ana-logos meaning "proportion" or "ratio." The most general sense of analogous is thus "corresponding in some particular," making it synonymous with "similar, alike, comparable." The noun form, analogue (analogin the US), is something having an analogy--a partial similarity on which a comparison may be based--with something else. (Random House Dictionary).
In the lingo of computing, this definition has been extended and made more particular. Analogue is
the term applied to any device, usually electronic, that represents values by a continuously variable physical property, such as voltage in a electronic circuit...[A]nalog means both variation and proportion. An analog device can represent an infinite number of values within the range the device can handle. In contrast, digital representation maps values onto discrete numbers, limiting the possible range of values to the resolution of the digital device. (Microsoft Computer Dictionary, 19)
Analogue data is "represented by continuously variable changes in a physical property such as voltage, fluid pressure, or rotation." Essentially, analogue means "continuously variable" when referring to computers.
An analogue-to-digital converter (ADC) translates analogue signals to digital signals. While the analogue signal is continuously variable within a range of values, a digital signal consists of discrete numeric values represented by binary patterns of 0's and 1's. An A-D converter periodically measures (samples) the analogue signal and converts each measurement to the corresponding digital value. An A-D converter, for example, can be used to convert sound represented as an analogue electric signal--a sine wave--to a series of digital samples that can be stored in memory, on hard disk, or on a compact disk. It is this conversion that has revolutionized the way information is recorded, stored, transmitted, and integrated.
"The primary characteristics of an ADC are the number of samples per second it can convert and the precision of each sample in bits. For example, high quality sound stored on compact disc is often digitized at 48,000 samples per second and 16 bits per sample, rendering up to 65,536 voltage levels in each sample."(Microsoft,19-20)
In Split Screen, David Ellis elaborates on the above definition of analogue: "In analog signal processing, some property of the signal, such as its voltage, magnetic field or frequency, varies continuously such that that output is analogous to the input"(228). For a vinyl LP playing on a stereo system, the needle in the tone arm follows the wavy grooves in the record surface, and this movement is translated into a continuously varying magnetic field in the pickup head. Variations in the electrical signal flow to the amplifier where they are filtered and amplified,then converted by loudspeakers into mechanical movement of the speaker elements to recreate an audible signal. At each stage, analog circuits recreate continuous analogies or approximations of the information that is carried by the electrical signal.
While analog signals are continuous--like waves--digital signals are discrete--like numbers. The discrete (and unambiguous) quality of digital signals means that when digitally encoded audio or video information is amplified, copied or otherwise processed, the output is identical to the input. As noted above, the quality of the digital signal is dependent on the number of samples taken at the input stage.
"Analogue signals are application specific; digital signals are generic" (Ellis 229). Ellis illustrates this important principle by asserting that the analogue information generated by the wavy grooves of the LP "can't be altered or enhanced in any way. It can only be played back, with a greater or lesser degree of fidelity, just as it was recorded in the vinyl. Digital signals on the other hand, are not dependent for their existence on a particular physical medium....Most importantly, they can be reprocessed and enhanced indefinitely with the aid of computers." The CD player and the digital processor of the computer "speak the same language of binary digits and handle information in exactly the same logical way" (229).This characteristic of digital media is essential for the application of compression algorithms in image and music files.
Digitcomes from the Latin digitus --finger or toe--two handy measuring devices associated with the Arabic numerals 1 to 9 and 0. Digital is virtually synonymous with binary when referring to computers, which process information coded as combinations of binary digits (bits). One bit can represent at most two values; 2 bits, four values; 8 bits, 256 values etc. Values that fall between two numbers are represented as either the higher or lower of the two. (Microsoft Dictionary120) Binary digital computers are based on two states, logical ON and OFF, represented by two voltage levels, arrangements of which are used to represent all types of information--numbers, letters, graphics symbols, and program instructions. Digital recording converts information to "strings of 1's and 0's that can be physically represented on a storage medium. In a computer, a magnetic disk drive converts electric impulses representing 1's and 0's to magnetic flux changes in which magnetic particles on a disk are oriented in one of two possible directions. Taken together, the alignment of all the particles on the disk represent digitally recorded information" (121). In a digital signal, information is represented by "discreet states"--for example, high voltages and low voltages--rather than by continuously variable levels in a continuous stream, as in an analogue signal.
From its origins, the technology of photography has been based on the effect of continuously varying light on chemicals, whether those chemicals are found on a metal, glass, or celluloid medium. Photography has claimed to provide images so closely analogous to reality that it has been used to record the facts of life: news, commercial products, the moments of a life, landscapes, technical illustrations and so on. Of course, there are some who have also made the case that the composition, framing, and selection process of photography ideally suits it for promotional and propagandistic purposes, made all the more powerful for the apparent documentary qualities of the light impinging on chemical technology. The advent of digital photography and image manipulation in the 1980's provided commentators an ideal opportunity to reassess the "objective" nature of the medium.
Digital photography differs from conventional photography in that a digital camera does not use a silver-halide based film to capture an image. A digital camera exposes the light reflecting off an image to a CCD (charge-coupled device) element that is covered with thousands of semi-conductors overlaid with green, red, and blue filters. Photons of light excite each element of the CCD, which converts photons to electrical information that is then transformed to digital data and stored in a solid-state memory or hard disk. After the image has been captured, some digital camera systems require that a camera be connected to a computer by a cable and the image downloaded to the computer using software supplied with the camera. A photograph can also be digitized by a scanner that converts lines and shading to combinations of 0's and 1's by sensing different intensities of light and dark. Once in a digitized form, the image may be altered--in a program like Photoshop--in an increasing range of eye-opening, reality-shaping ways.
In his book Digital Mantras, Steven Holtzman considers how the digitization of image and sound will stimulate artists and musicians not just to make familiar effects in a new way, but to create new effects which are idiomatic to the computer. Just as computer interfaces use familiar analogies such as the desktop,trash bin, file folder and notepad to make computers less threatening, so do many programs use analogies to make the digital operation seem familiar to the user: the digital paintbrush or spraycan, and color palettes in visual programs; frequency modulation in audio programs--conceptual terminology that borrows from existing paradigms. Faced with the new digital technology, the human mind tends to resort to analogies to describe the new information-processing environment. Holtzman asks the difficult question, "What means of expression are idiomatic to computers?" Holtzman then goes on to suggest that, in terms of music, the musician consider the ways that the computer creates a sound:
Perhaps the idiomatic sounds of a computer can be found in representing sound the way a computer creates sounds: in terms of machine instructions. Not Fourier synthesis, not frequency modulation synthesis, but store, retrieve, add, subtract, multiply, divide, and logical shift. (243)
In the shift from analog to digital signal processing, Holtzman is suggesting, old paradigms are expressed as analogies to promote familiarity and acceptance of the new technology; these analogies also tend to limit the ways in which we are able to use the new digital technologies creatively.
McLuhan called this the "rearview mirror syndrome," a situation extensively documented by media analysts: early mechanical printing replicated manuscripts; early photographs mimicked painting; radio broadcast concerts and revues; early television presented plays and radio-style news reports; the internet adopts old business models, or replicates forms of entertainment like streaming video (aka television).
We are now faced with the rapid integration of digital technologies into our lives, and the choices can be baffling. Do we trade in an excellent analogue camera for a digital camera that loads images directly into our desktop computer? Do we subscribe to the digital or analogue cellphone plan? Should we hang on to our collection of vinyl? 8-track tapes? cassettes? How do we compose music using a piece of software and a keyboard designed for typing? Does the convenience of email give us more time, or more responsibility? The answers to these and thousands of similar questions have become part of our everyday news and social interaction. As Nicholas Negroponte pointed out in his 1995 Being Digital, our world is fast exchanging the trade in atoms for the trade in bits: "The change from atoms to bits is irrevocable and unstoppable," he claims (4). Many of us may feel exactly as Negroponte does--that our present is being determined by technology. However, there is also very much about human life that is not easily converted from the analogue to the digital, and it is on making that distinction that our cultural survival depends.