# Difference between Analog and Digital Signals

A signal is simply an indication of movement of something. It can be current, light, music or even the heat. Being quite crucial to science, signals have been widely divided into two classes in order to ease out their study. Analog and digital are types of signals that follow different mannerisms in propagating any signal. Signals that follow analog methodology propagate in such a manner that they can be studied at any instant of time. On the other hand, digital signals can be defined at discrete values which are a whole number. For instance, consider a sound signal that can be measured in time interval between 0 second to 10 seconds. When it comes to measuring an analog signal, it can be measure at 0 seconds, 0.5 seconds, 0.7 seconds, 1.5 seconds and such values which can be in decimal. The numbers after decimal can extend to any limit of specificity. When the same signal is studied in a form of a digital signal, it can be only measured at discrete levels such as 1, 2, 3, 4 and such values which can only be defined at non decimal numbers.

Both Analog and Digital Signals (Image Courtesy of levents/sxc.hu)

Other characteristic that creates significant difference between analog and digital signals is the amplitude limitation. Analog signals are independent from the bounds of amplitude. These signals can have as much as amplitude. The amplitude depends on how intensive the input signal is. Usually, louder or brighter the input signal is, higher is the voltage. In digital signals, amplitude has only two states i.e. ON and OFF. At ON position, the signal has high amplitude meaning it contains information while at the OFF state, the signal has low amplitude which usually means that no significant information is being conveyed through the signal. The signals that are transmitted in analog signals have no defined form or shape but digital signals have a defined shape such as a square or a rectangle. Both the signal transmission methodologies have their pros and cons and are used in almost every electrical and electronic application as per the specification of the device.

##### Basics of Analog  and Digital Signal

Analog signals are the usual simple signals which can be observed in a normal human voice or the wind in the ambient conditions. Analog signals can be literally called a wave. These signals are what the nature has given humans. The way the water hits the rocks, the manner in which sand moves in the ocean, the essence which defines how bright the sunlight is and several natural factors are one or the other form of analog signals.In commercial applications, analog signal is found in audio and video applications. Being specific into audio, analog signals are what that is released from the speaker or the headphones.  Analog signals are used in transmission when the data is required to be sent at smaller distances. For transmission of analog signals, both the transmitter and the receiver are located in the vicinity of each other so that information can be send easily or the transmitter should have repeaters that can repower data and transmit it to the next destination.

Digital signals are a processed form of analog signals, purely synthetic, which has been created for electronics and communications purposes. These signals are a requirement of transmitting information in a simple ON and OFF format. Digital signals are made using converters and signal levelers that convert an analog signal to a digital one. Creation of digital signals is an expensive task and is only carried out when information has to be sending to longer distance or the data is quite significant that it cannot be lost. In the field of communications, digital signals are used in cellular communications, internet networking. The high data exchange modes such as 3G, Bluetooth etc. are a result of digital communications.  In the field of electronics, digital signals are used in creating new codes for computer and mobile circuitry. Devices such as multiplexers, digital gates and other combinational and sequential circuit designs are some of the wide known applications of digital signal utilization.

##### Conversion from Analog to Digital and Vice Versa

Analog to digital converters (ADC) are used to convert analog signal to a digital signal. The technical word for creating a digital signal out of an analog signal is called quantization. The major principle that is used inquantizationis the rate with which signal is converted to digital levels. Analog signals are sampled at short intervals of time in order to be created into digital. The rate by which they are sampled is called sampling rate and for a proper conversion, it is mandatory for the sampling rate to be at least twice as fast as the rate with which the signal repeats itself (frequency).  When the sampling rate is more than the frequency, it is easy to digitize the signal and least amount of information is lost in the process. The condition when the sampling rate is unable to fulfill the aforementioned criteria is called Aliasing. In this condition, the digital signal created is unable to generate the full amount of information that the original analog signal carried. Thus, sampling rate has to be kept constantly boosted up so that the data is kept intact while the signal is converted from analog to digital.

Similar to analog-digital converters (ADC), digital to analog converters are used in order to convert the digital signals back to their analog signal format. These converters are also dependent on the sampling rate which the ADC converters use. They can create a true analog signal only when the ADC converters are made to work at sampling rates at least equal to the double of the original signal frequency.

##### Comparison between analog and digital

Difference between analog and digital signals can be made on several grounds out of which economic and technological ones are the most talked about.

Under the technological part, Digital signals take a clear cut majority. Transmission of digital signals is fixed in terms of amplitude; the signals have a more balanced structure as well as data remains protected through these signals. Analog signals, on the other hand, don’t have any defined level of uniformity and controllability in terms of amplitude. As a result, these signals are more susceptible to distortion. This significantly reduces the signal’s chances for being transmitted for long distances.  Moreover, these signals can be easily intervened and disturbed. The transmitter and receiver circuits also become more complex due to unpredictability of the signal which in turn increases the complications in the circuitry of these signals.

In terms of economic aspects, analog signals are one of the most economic type of signals in the case when there signal is just to be transmitted over smaller distances. In television broadcast, analog systems are quite used. Also in FM and AM types of radio transmissions, such systems are used. Digital signal generating circuits are usually sophisticated in terms of electronic components. These systems are expensive and are used in long distance communication. Some luxurious home appliances brands also exploit digital signal technique for better outputs.

In some systems, both the types of signals are used. In some amplitude dependent systems which just require data to be sent over large distances, signal is first converted to digital in the transmitter and is then converted to analog in the receiver. Such technique is used in signal repeaters which receive and retransmit the signal.