Types of signals. Differences between analog and digital sound

The average person does not think about the nature of signals, but about the difference between analog and digital broadcasting or formats - sometimes you have to. By default, it is believed that analog technologies are becoming a thing of the past, and will soon be completely replaced by digital ones. It’s worth knowing what we give up in favor of new trends.

Analog signal- a data signal described by continuous functions of time, that is, its oscillation amplitude can take any value within the maximum.

Digital signal- a data signal described by discrete functions of time, that is, the amplitude of oscillations takes only strictly defined values.

In practice, this allows us to say that analog signal is accompanied by a large amount of interference, while digital successfully filters them out. The latter is capable of restoring the original data. In addition, a continuous analog signal often carries a lot of unnecessary information, which leads to its redundancy - several digital signals can be transmitted instead of one analog signal.

If we talk about television, and it is this area that worries most consumers with its transition to “digital,” then we can consider the analog signal to be completely obsolete. However, for now, analog signals can be received by any equipment designed for this purpose, while digital signals require special equipment. True, with the spread of digital television, there are fewer and fewer analogue TVs and the demand for them is catastrophically decreasing.

One more important characteristic signal - safety. In this regard, analog demonstrates complete defenselessness against outside influences or intrusions. The digital one is encrypted by assigning a code from radio pulses to it, so that any interference is excluded. On long distances It is difficult to transmit digital signals, therefore a modulation-demodulation scheme is used.

Conclusions website

1. The analog signal is continuous, the digital signal is discrete.
2. When transmitting an analog signal, there is a higher risk of clogging the channel with interference.
3. The analog signal is redundant.
4. The digital signal filters out interference and restores the original data.
5. The digital signal is transmitted in encrypted form.
6. Multiple digital signals can be sent instead of one analog signal.

Any signal, analog or digital, is electromagnetic vibrations, which propagate with a certain frequency, depending on what signal is transmitted, the device receiving this signal translates it into text, graphic or audio information, convenient for perception by the user or the device itself. For example, a television or radio signal, a tower or radio station can transmit both analog and, at the moment, digital signal. The receiving device, receiving this signal, converts it into image or sound, complementing text information(modern radios).

Sound is transmitted to analogue form and already after receiver is converted into electromagnetic oscillations, and as already mentioned, the oscillations propagate with a certain frequency. The higher the frequency of the sound, the higher the vibrations will be, which means the output sound will be louder. In general terms, an analog signal propagates continuously, while a digital signal propagates intermittently (discretely).

Since the analog signal propagates constantly, the oscillations are summed up and a carrier frequency appears at the output, which in this case is the main one and the receiver is configured for it. In the receiver itself, this frequency is separated from other vibrations, which are already converted into sound. The obvious disadvantages of transmitting using an analog signal include − large number interference, low security of the transmitted signal, as well as a large amount of transmitted information, some of which is superfluous.

If we talk about a digital signal, where data is transmitted discretely, it is worth highlighting its obvious advantages:

• high level of protection of transmitted information due to its encryption;
• ease of digital signal reception;
• absence of extraneous “noise”;
• digital broadcasting can provide a huge number of channels;
• high quality of transmission - the digital signal provides filtering of received data;

To convert an analog signal to a digital signal and vice versa, special devices are used - an analog-to-digital converter (ADC) and a digital-to-analog converter (DAC). The ADC is installed in the transmitter, the DAC is installed in the receiver and converts the discrete signal to analog.

Regarding security, why is a digital signal more secure than an analog signal? The digital signal is transmitted in encrypted form and the device that receives the signal must have a code to decrypt the signal. It is also worth noting that the ADC can also transmit the digital address of the receiver; if the signal is intercepted, it will be impossible to completely decrypt it because part of the code is missing - this approach is widely used in mobile communications.

To summarize, the main difference between an analog and digital signal is the structure of the transmitted signal. Analog signals are a continuous stream of oscillations with varying amplitude and frequency. A digital signal consists of discrete oscillations, the values ​​of which depend on the transmitting medium.

With these words, John began his Gospel, describing times beyond the borders of our era. We begin this article with no less pathos, and seriously declare that in the business of broadcasting “in the beginning there was a signal.”

In television, as in all electronics, the signal is the basis. When we talk about it, we mean electromagnetic oscillations that propagate in the air with the help of a transmitting antenna and cause current fluctuations in the receiving antenna. The broadcast wave can be presented in both continuous and pulsed form, which significantly affects the final result - the quality of TV reception.

What's happened analog television? This is television, familiar to everyone, which was seen by our parents’ parents. It is broadcast in an unencrypted way, its basis is an analog signal, and it is received by an ordinary analog TV, familiar to us from childhood. Currently, in many countries the process of digitizing an analog signal is underway, and therefore terrestrial television. In some European countries this process has already been completed and terrestrial analogue TV has been switched off. There are reasons for this, which this article suggests to understand.

Differences between a digital signal and an analog signal

For most people, the difference between an analog and digital signal can be quite subtle. And yet, their difference is significant and lies not simply in the quality of the television broadcast.

An analog signal is the received data that we see, hear and perceive as the world that surrounds us. This method of generating, processing, transmitting and recording signals is traditional and still very widespread. The data is converted into electromagnetic waves, reflecting the frequency and intensity of the phenomena according to the principle of complete correspondence.

A digital signal is a set of coordinates that describe an electromagnetic wave, which is not inaccessible to direct perception, without decoding, because is a sequence of electromagnetic pulses. Speaking about discreteness and continuity of signals, they mean, respectively, “taking values ​​from a finite set” and “taking values ​​from an infinite set.”

An example of discreteness would be school grades, which take values ​​from the set 1,2,3,4,5. In fact, a digital video signal is often created by digitizing an analog signal.

Moving away from theory, in reality we can highlight the following key differences between analog and digital signals:

1. analogue television is vulnerable to interference that introduces noise into it, while the digital impulse is either completely blocked by interference and is absent, or arrives in its original form.
2. Any device whose operation is based on the same principle as the transmitter’s broadcast can receive and read an analog signal. The digital wave is intended for a specific “addressee”, and therefore is resistant to interception, because securely encoded.

Image quality

The quality of the TV picture provided by analog TV is largely determined by the TV standard. The frame that carries analog broadcast includes 625 lines with an aspect ratio of 4x3. Thus, the old kinescope displays an image from television lines, while a digital image is made up of pixels.

With poor reception and interference, the TV will “snow” and hiss, not providing the viewer with image and sound. In attempts to make improvements to this situation, at one time, it was implemented.

Other options

Despite the rapid development of electronic technology and the advantages of digital signal over analogue, there are still areas in which analogue technology is indispensable, such as professional processing sound. But, although the original recording may be no worse than the digital one, after editing and copying it will inevitably be noisy.

Here is a set of basic operations that can be performed with an analog stream:

• strengthening and weakening;
• modulation, aimed at reducing its susceptibility to interference, and demodulation;
• filtering and frequency processing;
• multiplication, summation and logarithm;
• processing and changing the parameters of its physical quantities.

Features of analogue and digital television

The philistine judgment about the collapse of terrestrial TV and the transition to broadcasting technologies of the future is somewhat unfair, if only because TV viewers are replacing the concepts: terrestrial and analog TV. After all, terrestrial television is usually understood as any television broadcast over a terrestrial radio channel.

Both “analog” and “digital” are types of terrestrial TV. Despite the fact that analogue television differs from digital television, they general principle broadcast is identical – television tower broadcasts channels and guarantees a high-quality signal only within a limited radius. At the same time, the digital coverage radius is shorter than the range of the unencoded stream, which means that repeaters must be installed closer to each other.

But the opinion that “digital” will ultimately surpass “analog” is true. TV viewers in many countries have already become “witnesses” of the conversion of an analogue signal to a digital one and are thoroughly enjoying watching TV programs in HD quality.

Features of broadcast television

The existing terrestrial television system uses analog signals to transmit television products. They spread through waves with high level vibrations reaching terrestrial antennas. In order to increase the broadcast coverage area, repeaters are installed. Their function is to concentrate and amplify the signal, transmitting it to remote receivers. Signals are transmitted at a fixed frequency, so each channel corresponds to its own frequency and is assigned to the TV in numerical order.

Advantages and disadvantages of digital television broadcasting

Information transmitted using digital code, contains virtually no errors or distortions. The device that digitizes the original signal is called analog-to-digital converter(ADC).

To encode pulses, a system of ones and zeros is used. To read and convert BCD code, a device called a digital-to-analog converter (DAC) is built into the receiver. There are no half values ​​for either the ADC or DAC, such as 1.4 or 0.8.

This method of encrypting and transmitting data has given us a new TV format, which has many advantages:

• changing the strength or length of the pulse does not affect its recognition by the decoder;
• uniform broadcast coverage;
• unlike analogue broadcasting, reflections from obstacles of the converted broadcast add up and improve reception;
• broadcast frequencies are used more efficiently;
• Can be received on analog TV.

Difference digital television from analog

The easiest way to notice the difference between analogue and digital broadcasting is to present the final characteristics of both technologies in the form of a table.

TV antenna sensitivity

There is no universal recipe for choosing the ideal antenna, but there is mandatory requirements, which must be met in order for it to accept analog and digital signals. As the distance from the broadcast object increases, these requirements increase. In particular, to the sensitivity of the receiver - its ability to pick up weak-intensity television signals. Often they are the cause of a blurry image. This problem can be solved with the help of, which significantly increases the sensitivity of the antenna and removes the question: how to connect it to digital television? The same TV, and the same antenna, only an over-the-air digital tuner will appear near the TV.

What is an antenna radiation pattern

In addition to the sensitivity of the antenna, there is a parameter that determines the extent to which it is able to focus energy. It is called directional gain or directivity, and is the ratio of the radiation density in a given direction to the average radiation density.
A graphical interpretation of this characteristic is the antenna radiation pattern. At its core, it is a three-dimensional figure, but for ease of work it is expressed in two planes located perpendicular to each other. Having such a flat diagram at hand and comparing it with a map of the area, you can plan the antenna reception area for an analog video signal. Also from this graph you can extract a number of useful practical characteristics of the TV antenna, such as the intensity of lateral and reverse radiation and the protective coefficient.

Which signal is better

It should be recognized that, despite many improvements implemented in the field of analog representation of information, this method of broadcasting has retained its shortcomings. These include distortion during transmission and noise during playback.

Also, the need to convert an analog signal to a digital one is caused by the unsuitability of the existing recording method for storing information in semiconductor memory.

Unfortunately, existing TV has virtually no obvious advantages over digital, excluding the possibility of receiving a signal with a regular TV antenna and sharing it between TVs.

Digital electronics are now increasingly replacing traditional analog electronics. Leading companies producing a wide variety of electronic equipment, they are increasingly announcing a complete transition to digital technology.

Advances in electronic chip production technology have ensured the rapid development of digital technology and devices. The use of digital methods of signal processing and transmission can significantly improve the quality of communication lines. Digital methods signal processing and switching in telephony make it possible to reduce the weight and size characteristics of switching devices several times, increase communication reliability, and introduce additional functionality.

The emergence of high-speed microprocessors and microcircuits RAM large volumes, small-sized devices for storing information on large-volume hard media made it possible to create fairly inexpensive universal personal electronic computers(computers), which have found very wide application in everyday life and production.

Digital technology is indispensable in telesignaling and telecontrol systems used in automated production, control of remote objects, for example, spaceships, gas pumping stations, etc. Digital technology has also taken a strong place in electrical and radio measuring systems. Modern devices recording and reproducing signals is also unthinkable without the use digital devices. Digital devices are widely used to control household appliances.

It is very likely that digital devices will dominate the electronics market in the future.

First, let's give some basic definitions.

Signal is any physical quantity (for example, temperature, air pressure, light intensity, current strength, etc.) that changes over time. It is thanks to this change in time that the signal can carry some information.

Electrical signal is an electrical quantity (for example, voltage, current, power) that changes over time. All electronics basically work with electrical signals, although lately increasingly used light signals, which represent the time-varying intensity of light.

Analog signal is a signal that can take any value within certain limits (for example, the voltage can smoothly change from zero to ten volts). Devices that work only with analog signals are called analog devices.

Digital signal is a signal that can take only two values ​​(sometimes three values). Moreover, some deviations from these values ​​are allowed (Fig. 1.1). For example, voltage can take two values: from 0 to 0.5 V (zero level) or from 2.5 to 5 V (unit level). Devices that work exclusively with digital signals are called digital devices.

In nature, almost all signals are analog, that is, they change continuously within certain limits. This is why the first electronic devices were analog. They converted physical quantities into voltage or current proportional to them, performed some operations on them, and then performed inverse conversions into physical quantities. For example, a person’s voice (air vibrations) is converted into electrical vibrations using a microphone, then these electrical signals are amplified by an electronic amplifier and using speaker system again converted into air vibrations, into a louder sound.

Rice. 1.1. Electrical signals: analog (left) and digital (right).

All operations performed by electronic devices on signals can be divided into three large groups:

Processing (or transformation);

Broadcast;

Storage.

In all these cases, useful signals are distorted by parasitic signals - noise, interference, interference. In addition, when processing signals (for example, during amplification, filtering), their shape is also distorted due to imperfection, non-ideality electronic devices. And when transmitted over long distances and during storage, the signals are also weakened.

Rice. 1.2. Distortion by noise and interference of an analog signal (left) and a digital signal (right).

In the case of analog signals, all this significantly degrades the useful signal, since all its values ​​are allowed (Fig. 1.2). Therefore, every conversion, every intermediate storage, every transmission via cable or air degrades the analog signal, sometimes even to the point of its complete destruction. We must also take into account that all noise, interference and interference are fundamentally not amenable to accurate calculation, therefore it is absolutely impossible to accurately describe the behavior of any analog devices. In addition, over time, the parameters of all analog devices change due to aging of the elements, so the characteristics of these devices do not remain constant.

Unlike analog signals, digital signals, which have only two permitted values, are much better protected from noise, interference and interference. Small deviations from the permitted values ​​do not distort the digital signal in any way, since there are always zones of permissible deviations (Fig. 1.2). That is why digital signals allow for much more complex and multi-stage processing, much longer lossless storage and much higher quality transmission than analog signals. In addition, the behavior of digital devices can always be absolutely accurately calculated and predicted. Digital devices are much less susceptible to aging, since small changes in their parameters do not affect their functioning in any way. In addition, digital devices are easier to design and debug. It is clear that all these advantages ensure the rapid development of digital electronics.

However, digital signals also have a major drawback. The fact is that a digital signal must remain at each of its allowed levels for at least some minimum time interval, otherwise it will be impossible to recognize it. And an analog signal can take on any value in an infinitesimal time. We can say it another way: an analog signal is defined in continuous time (that is, at any point in time), and a digital signal is defined in discrete time (that is, only at selected points in time). Therefore, the maximum achievable performance of analog devices is always fundamentally greater than that of digital devices. Analog devices can handle more rapidly changing signals than digital ones. Speed ​​of information processing and transmission analog device can always be made higher than the speed of its processing and transmission by a digital device.

In addition, a digital signal transmits information only in two levels and by changing one of its levels to another, while an analog signal also transmits information with each current value of its level, that is, it is more capacious in terms of information transmission. Therefore, to transmit the amount of useful information contained in one analog signal, it is most often necessary to use several digital signals (usually from 4 to 16).

In addition, as already noted, in nature all signals are analog, that is, to convert them into digital signals and for the reverse conversion, the use of special equipment (analog-to-digital and digital-to-analog converters) is required. So nothing comes for free, and the price to pay for the benefits of digital devices can sometimes be unacceptably high.

Signals are information codes that people use to convey messages to information system. The signal can be given, but it is not necessary to receive it. Whereas a message can only be considered a signal (or a set of signals) that was received and decoded by the recipient (analog and digital signal).

One of the first methods of transmitting information without the participation of people or other living beings were signal fires. When danger arose, fires were lit sequentially from one post to another. Next, we will consider the method of transmitting information using electromagnetic signals and will dwell in detail on the topic analog and digital signal.

Any signal can be represented as a function that describes changes in its characteristics. This representation is convenient for studying radio engineering devices and systems. In addition to the signal in radio engineering, there is also noise, which is its alternative. No noise useful information and distorts the signal by interacting with it.

The concept itself makes it possible to abstract from specific physical quantities when considering phenomena related to the encoding and decoding of information. Mathematical model signal in research allows you to rely on the parameters of the time function.

Signal types

Signals by physical environment Information carriers are divided into electrical, optical, acoustic and electromagnetic.

According to the setting method, the signal can be regular or irregular. A regular signal is represented as a deterministic function of time. An irregular signal in radio engineering is represented by a chaotic function of time and is analyzed by a probabilistic approach.

Signals, depending on the function that describes their parameters, can be analog or discrete. Discrete signal, which has been quantized is called a digital signal.

Signal Processing

Analog and digital signals are processed and directed to transmit and receive information encoded in the signal. Once information is extracted, it can be used for various purposes. In special cases, information is formatted.

Analog signals are amplified, filtered, modulated, and demodulated. Digital data can also be subject to compression, detection, etc.

Analog signal

Our senses perceive all information entering them in analog form. For example, if we see a car passing by, we see its movement continuously. If our brain could receive information about its position once every 10 seconds, people would constantly get run over. But we can estimate distance much faster and this distance is clearly defined at each moment of time.

Absolutely the same thing happens with other information, we can evaluate the volume at any moment, feel the pressure our fingers exert on objects, etc. In other words, almost all information that can arise in nature has analog view. The easiest way to transmit such information is through analog signals, which are continuous and defined at any time.

To understand what analog looks like electrical signal, you can imagine a graph that displays amplitude on the vertical axis and time on the horizontal axis. If we, for example, measure the change in temperature, then a continuous line will appear on the graph, displaying its value at each moment in time. To transmit such a signal using electric current, we need to compare the temperature value with the voltage value. So, for example, 35.342 degrees Celsius can be encoded as a voltage of 3.5342 V.

Analog signals used to be used in all types of communications. To avoid interference, such a signal must be amplified. The higher the noise level, that is, interference, the more the signal must be amplified so that it can be received without distortion. This method of signal processing spends a lot of energy generating heat. At the same time amplified signal may itself cause interference to other communication channels.

Nowadays analog signals are still used in television and radio to convert input signal in microphones. But in general, this type of signal is being replaced or replaced by digital signals everywhere.

Digital signal

A digital signal is represented by a sequence of digital values. The most commonly used signals today are binary digital signals, as they are used in binary electronics and are easier to encode.

Unlike the previous signal type, a digital signal has two values ​​“1” and “0”. If we remember our example with temperature measurement, then the signal will be generated differently. If the voltage supplied by the analog signal corresponds to the value of the measured temperature, then a certain number of voltage pulses will be supplied in the digital signal for each temperature value. The voltage pulse itself will be equal to “1”, and the absence of voltage will be “0”. The receiving equipment will decode the pulses and restore the original data.

Having imagined what a digital signal will look like on a graph, we will see that the transition from zero to maximum is abrupt. It is this feature that allows the receiving equipment to “see” the signal more clearly. If any interference occurs, it is easier for the receiver to decode the signal than with analog transmission.

However, it is impossible to reconstruct a digital signal with a very high noise level, whereas from analog type if there is a large distortion, it is still possible to “fish out” the information. This is due to the cliff effect. The essence of the effect is that digital signals can be transmitted over certain distances, and then simply stop. This effect occurs everywhere and is solved by simply regenerating the signal. Where the signal breaks, you need to insert a repeater or reduce the length of the communication line. The repeater does not amplify the signal, but recognizes its original form and outputs it exact copy and can be used as desired in the circuit. Such signal repetition methods are actively used in network technologies.

Among other things, analog and digital signals also differ in the ability to encode and encrypt information. This is one of the reasons for the transition of mobile communications to digital.

Analog and digital signal and digital-to-analog conversion

There's a little more to say about how analog information is transmitted over digital channels communications. Let's use examples again. As already mentioned, sound is an analog signal.

What's happening in mobile phones that transmit information via digital channels

Sound entering the microphone undergoes analog-to-digital conversion (ADC). This process consists of 3 steps. Individual signal values ​​are taken at equal intervals of time, a process called sampling. According to Kotelnikov’s theorem about bandwidth channels, the frequency of taking these values ​​should be twice as high as the most high frequency signal. That is, if our channel has a frequency limit of 4 kHz, then the sampling frequency will be 8 kHz. Next, all selected signal values ​​are rounded or, in other words, quantized. The more levels created, the higher the accuracy of the reconstructed signal at the receiver. Then all values ​​are converted to binary code, which is transmitted to base station and then reaches another subscriber, who is the receiver. A digital-to-analog conversion (DAC) procedure takes place in the receiver's phone. This is a reverse procedure, the goal of which is to obtain a signal at the output that is as identical as possible to the original one. Next, the analog signal comes out in the form of sound from the phone speaker.