Understanding the nature of digital signals, binary, and other multi-level signal types do require an explanation of the two most prominent telecommunications types that exist, and examples of how they are applicable to specific devices, the binary is association and its function. (Please note that the majority of the information below are extracts from various websites, used to validate and support a theoretical premise; on which an understanding of multilevel signals exist. )
Analog and Digital Signals
The term “analog” comes from the word “analogous” meaning something is similar to something else. It is used to describe devices that turn the movement or condition of a natural event into similar electronic or mechanical signals. For example a non-digital watch contains a movement that is constantly active in order to display time, which is also constantly active. Our time is measured in ranges of hours, minutes, seconds, months, years, etc. The display of a watch constantly tracks time within these ranges. In effect the data represented on a watch may have any number of values within a fairly large range. The watch’s movement is analogous to the movement of time. In this respect the data produced is analog data.
Digital signals, on the other hand, are distinctively different. Digital signals don’t have large ranges, nor do they reflect constant activity. Digital signals have very few values. Each signal is unique from a previous digital value and unique from one to come. In effect, a digital signal is a snapshot of a condition and does not represent continual movement. Binary
Every electronic signal is broken down into binary language, classified as ‘0’ and ‘1’. The most obvious example of digital data is that communicated on-board a computer. Since a computer’s memory is simply a series of switches that can either be on or off, digital data directly represents one of these two conditions. We typically represent this on and off status with 1s and 0s where 1 represents an “on” bit and 0 represents “off”.
The nature of analog is to closely capture the essence of natural phenomenon, with its action and subtlety. Digital data can only attempt to capture natural phenomenon by “sampling” it at distinct intervals, creating a digital representation composed of 1s and 0s. Obviously, if the interval between samples is too large, the digital representation less accurately represents the phenomenon. If the sampling occurs at too short of an interval, then an inordinate amount of digital resources may be utilized to capture the phenomenon. The changes involved may not be significant enough to warrant so frequent a sampling for accuracy’s sake. To digitally represent sound authentically, a sample must be taken over 44, 500 times per second.
When copying an analog signal from one generation to another, deterioration of the original signal occurs. A prime example is when we copy a videotape. Since video recorders are analog machines, copying a tape several times results in the accumulation of unwanted analog values called “noise”. Eventually these signals become so evident, that the original analog signal is compromised and the video “dub” suffers from intense graininess and poor audio sound. Our technology is limited in the transmission and duplication of analog signals because of the infinite number of values that are allowable.
Digital signals, however, have basically two values. It is much easier to work with two values rather than an infinite number. Consequently our current level of technology allows us to maintain the original quality of a digital signal. With a value of “on” or “off”.
Advantages and Disadvantages
The main advantage of digital modulation over analog modulation is that in digital modulation, all input and output are in binary form. Anything that isn’t a ‘1’ or a ‘0’ is rejected by the modulator. This filters out a lot of noise that analog modulation lets through, which may not be related to the intended message.
Simple to evaluate and measure
Requires more bandwidth
Additional encoding (A/D) and decoding (D/A) circuitry
Digital modulation can easily detect and correct noise. Whereas analog modulation has little complexity digital modulation is preferred over analog because it is by far more secure. Digital modulation can easily detect and correct noise irregularities. Analog modulation though complex is minute when compared to digital modulation. Digital modulated signal can travel a longer distance compared to analog modulation. Analog signals have a great advantage over digital signals in that they have a much higher density that can present more refined information.
Disadvantages of the system include the tendency to create unwanted variations in the information transmission such as noise, which can occur in random patterns.
When a signal is copied and potentially re-copied, each subsequent version exhibits more of the random patterns, making information transmission harder and ultimately causes signal loss. In order to avoid these disadvantages, or at least mitigate their effects, the concept of modulation can be used. The base signal is modified in some way to help retain the information as it is transmitted. An example of this is when the amplitude of a waveform is altered in what is known as amplitude modulation. Other options for retaining an electric signal over different generations are by using increased shielding or different cable types twisted together.