Digital vs Analog

Being Analogue

We experience the world "in analogue" form. In almost every sense of the world we are analogue. What does this mean? One way of looking at it is that we actually live in four dimensions: one of which is time. We experience a smooth transition from one 'instant' in time to the next. In fact, for us, there ARE no "instants in time". Everything comes to us in a continuous flow. All of our senses are geared for this. Our vision involves a continuous flow of information being given to the brain to be interpreted. We experience sound in waves - again, a continuous flow of information. Our sense of touch involves a continuous flow of information. The same holds true for the rest of our senses. All living things experience the world (life) in an analogue fashion.

Analog	Digital
Continuous	Discrete
One flows into the next with no clear demarcation in between.	Consists of a series of 'events' each one having a finite shape with distinct 'borders'.
Real Numbers on a number line are continuous. For any two real numbers we can think of, there exist an infinite number of numbers in between. It is not possible to name the 'next' value.	Integer values are discrete. Given any two integer values, we can list exactly (precisely) how many numbers there are in between. Note though, that discrete and precise are not the same thing.

Being Digital

Computers are, of necessity, completely digital devices. They are totally discrete entities. Every computer has inside it a little clock. These days it takes the form of a crystal that vibrates - the vibration is a very regular thing and we use it to mark time like a musician's metronome. It vibrates very fast, and it is this vibration that is like the ticking of a clock. Each time this 'clock' ticks in the computer another thing gets to happen. Another instruction gets loaded, executed, etc. Every single thing that happens inside the machine marches to this drum. In some sense, for the computer there is no existence during the 'in between' stages.

The other aspect of being digital is that for any given thing we want to represent, we have only a finite number of numbers we can use to represent it. So for example, while the light spectrum is a continuous range, giving us an infinite number of colours, the computer can only represent a finite number of these. This means that there will be colours we can see in real life that we cannot represent on a computer (close, but no cigar). The combination of having what amounts to a finite number of symbols and a finite number of samples we can look at and remember limits the fidelity of anything we can store digitally. If the original thing we are trying to represent was continuous, then the digital version of it can only ever be an approximation.

Everything and anything we wish to represent on a computer must eventually be turned into some kind of number (it's all bits inside there), or a series of numbers. If we want to represent a song digitally, we have to find a way to transform a sound wave into a bunch of numbers. We do this by taking a bunch of samples at regular times, which are discrete instances in time, and mapping each one onto a number. If we do enough of these (say 44,000 per second), and then play them back, it once again sounds continuous.

All movies and animations rely on this principle too. Movies are made of a bunch of discrete, individual pictures that get flashed before our eyes at a particular rate. If this rate is fast enough, we perceive it as continuous movement, even though it is in fact a series of stills. This may be where some of the confusion about digital vs. analog comes from: because of the speeds and rates involved, much of the digital data coming to us from the computer LOOKS like it is continuous (analog) when in fact it is just many discrete samples being presented to us in rapid succession.

Analogue/Continuous

Digital/Discrete

A vinyl record

A CD

A symphony playing live

That same symphony recorded and stored on a computer.

A television signal (but probably not for much longer)

A movie on DVD

Older telephone lines

Cell phones

Time, distance, weight, mass, temperature, feelings?

Below is what happens when we take an analog signal and try to convert it into discrete, digital samples.

Some Definitions: from CDE (The Computer Desktop Encyclopedia)

Analog: A representation of an object that resembles the original. Analog devices monitor conditions, such as movement, temperature and sound, and convert them into analogous electronic or mechanical patterns. For example, an analog watch represents the planet's rotation with the rotating hands on the watch face. Telephones turn voice vibrations into electrical vibrations of the same shape. Analog implies continuous operation in contrast with digital, which is broken up into numbers.

Digital Traditionally, digital means the use of numbers and the term comes from digit, or finger. Today, digital is synonymous with computer.

Digital Means Original

The 0s and 1s of digital data mean more than just on and off. They mean perfect copying. When information, music, voice and video are turned into binary digital form, they can be electronically manipulated, preserved and regenerated perfectly at high speed. The millionth copy of a computer file is exactly the same as the original. While this continually drives the software industry crazy protecting its copyrights, it is nevertheless a major advantage of digital processing.

Quantization

(1) The division of a range of values into a single number, code or classification. For example, class A is 0 to 999, class B is 1000 to 9999 and class C is 10000 and above.

(2) In analog to digital conversion, the assignment of a number to the amplitude of a wave. The larger the range of numbers, the finer the increments can be measured, and the more the digital sample represents the analog signal.

Sampling Rate

In digitizing operations, the frequency with which samples are taken and converted into digital form. The sampling frequency must be at least twice that of the analog frequency being captured. For example, the sampling rate for hi-fi playback is 44.1 kHz, slightly more than double the 20 kHz frequency a person can hear. The sampling rate for digitizing voice for a toll-quality conversation is 8,000 times per second, or 8 kHz, twice the 4 kHz required for the full spectrum of the human voice. The higher the sampling rate, the closer real-world objects are represented in digital form.

Another attribute of sampling is quantizing, which creates a number for the sample. The larger the size of the sample, which is also known as resolution or precision, or just sample size, the more granular the scale and the more accurate the digital sampling.

	Copyright (C) 2004 Katrin Becker
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Last update: Thursday, February 26, 2004 11:34 PM

On the Distinction Between Digital and Analog, and What it means to "Be Analogue"