What is the difference between analog and digital signal?

TVs receive both analog and digital signals in the same way - in the form of electromagnetic pulses from the local TV tower or via the provider's cable. In both cases, you can watch your favorite TV shows and movies. What, then, is the difference between analogue and digital television and why is there a massive transition from one type of broadcasting to another in 2022? Let's figure out what the difference is and why “digital” is better than “analog”.

Signal parameters

• Signal power P ( t ) = s 2 ( t ) {\displaystyle P(t)=s^{2}(t)}
• Specific signal energy E sp = ∫ − ∞ ∞ s 2 ( t ) dt {\displaystyle E_{\text{sp}}=\int \limits _{-\infty }^{\infty }{s^{2}( t)dt}}
• The signal duration T {\displaystyle T} determines the time interval during which the signal exists (non-zero);
• Dynamic range is the ratio of the highest instantaneous signal power to the lowest:

D = 10 lg ⁡ P max P min {\displaystyle D=10\lg {\frac {P_{max}}{P_{min}}}}

• Signal spectrum width F {\displaystyle F} is the frequency band within which the main signal energy is concentrated;
• The signal base is the product of the signal duration and the width of its spectrum B = TF {\displaystyle B=TF} . It should be noted that there is an inversely proportional relationship between the width of the spectrum and the duration of the signal: the shorter the spectrum, the longer the duration of the signal. Thus, the size of the base remains practically unchanged;
• The signal-to-noise ratio is equal to the ratio of the useful signal power to the noise power;
• The volume of transmitted information characterizes the communication channel bandwidth required for signal transmission. It is defined as the product of the signal spectrum width and its duration and dynamic range:

V = FTD {\displaystyle V=FTD}

Analog TV

This television system uses an analog signal that arrives continuously to transmit pictures. Using an electronic circuit, this signal is converted into video and sound.

For analog TV, an antenna is sufficient. However, television of this kind today is considered obsolete and is gradually fading away. The main disadvantage of analogue broadcasting is the instability of the signal to interference, which contributes to the deterioration of picture quality.

Most modern states have long abandoned this type of television broadcasting, while other countries plan to do the same in the future. In Russia, the deadline for abandoning analog television was postponed several times to a later period.

General conclusion

Analog sound is what we hear and perceive as the world around us with our eyes.
Digital sound is a set of coordinates that describe a sound wave, and which we cannot hear directly without conversion to an analog signal. An analog signal recorded directly onto an audio cassette or vinyl cannot be re-recorded without loss of quality, while a wave in digital representation can be copied bit for bit.

Digital recording formats are a constant trade-off between the amount of coordinate accuracy versus file size, and any digital signal is only an approximation of the original analog signal. However, the different levels of technology for recording and reproducing a digital signal and storing on media for an analog signal give more advantages to the digital representation of the signal, similar to a digital camera versus a film camera.

Number

A signal can be represented as a sequence of discrete data. The data stream takes only two values:

• “0”—grounding or zero voltage;
• “1”—food. There is tension, no matter what the voltage is.

Data is converted into signals limited in magnitude and time. They are coded zero or one. Its basis is a bit that takes one of these values.

One bit will not convey much data. Therefore, they are combined into blocks.

How it works

The signal coming from the source is converted into a discrete (intermittent) signal, then encoded for transmission over communication channels. The antenna receives it. If the TV is equipped with an analog-to-digital converter (receiver), the TV will receive and process the signal.

Advantages and disadvantages of analog signal

The advantage of an analog signal is that it is in analog form that we perceive sound with our ears.
And although our auditory system converts the perceived sound stream into digital form and transmits it in this form to the brain, science and technology have not yet reached the point of connecting players and other sound sources directly in this form. Similar research is now being actively carried out for people with disabilities, and we enjoy exclusively analog sound. The disadvantage of an analog signal is the ability to store, transmit and replicate the signal. When recording to magnetic tape or vinyl, the quality of the signal will depend on the properties of the tape or vinyl. Over time, the tape demagnetizes and the quality of the recorded signal deteriorates. Each read gradually destroys the media, and rewriting introduces additional distortion, where additional deviations are added by the next media (tape or vinyl), reading, writing and signal transmission devices.

As digital radio and digital broadcasting continue to improve, the benefits will continue to grow. New digital radio features include the ability to pause a program and go back and forth to a portion of the broadcast. Finding stations will also become easier as technology advances. Listeners no longer have to search for the perfect tuning set placement for best reception.

How DACs build a wave

Mixed signal products are rarely created entirely in the analog or digital domain these days. Additionally, many traditionally analog systems now have firmware. These trends mean that analog and firmware developers need to understand the differences between their design disciplines to work together more effectively. But the fundamental ways designers work with analogs and firmware are very different, potentially leading to misunderstandings and conflict. Understanding the differences helps bridge the gap.

Making a copy of an analog signal is the same as copying a photograph by taking a photograph of it again.

How to understand whether you are watching digital or analog

Old TVs are not capable of receiving DTV on their own. To connect digital, they need an external set-top box. Modern devices are equipped with a special built-in DVB-T2 tuner.

To determine the signal type, you need to look at the TV menu. If ATV is set in the “Source” section, analog video content is viewed.

Other ways to determine the current broadcast type:

• TV channels broadcasting ATV are indicated by the letter A. If it is not there, then the channel shows new TV;
• the antenna plug is pulled out of the socket and retracted 0.5 cm. If the image has become illegible, but has not completely disappeared, analogue television is shown, if the image has completely disappeared - DTV;

  
  Effect of signal attenuation on the picture

• digital television does not show TV channels in the “home” region (it already broadcasts in full in MSC).

Uninterrupted broadcasting of which television is better?

In addition to depending on the distance of the tower, the analog signal has another big disadvantage - instability. This is because radio waves are very susceptible to weather conditions. Whether it's a thunderstorm, snow or storm, the signal will fade or extraneous noise will occur.

The digital frequency range is distinguished by its vastness and stability of reception/transmission. This is due to the fact that the information passes through the tower-satellite-antenna-tuner circuit. At the first stage, it is encoded and sent to a satellite, where it is amplified and transmitted to the receiver, decrypted by the tuner and a high-quality picture is displayed on the screen. This circuit does not give the signal a chance to get lost, which indicates its uninterrupted operation.

The analog signal is unreliable due to the way it is received. Digital broadcasting ensures stable reception of information due to its constant amplification.

What are the advantages of digital television

The complete transition to DTV is due to the fact that in many respects this technology is superior to ATV. So, the advantages of digital television over analogue are as follows:

• increased resistance to interference and, as a result, better picture and sound quality;
• the ability to broadcast images in HD and UHD quality, as well as in 3D format;
• stereo and surround sound support;
• a large number of TV channels;
• subtitle support;
• interactive TV systems that allow the viewer to influence the programs being watched (record, pause, move to the beginning of the program, and so on);
• the ability to switch between audio tracks in different languages ​​and select the subtitle language;
• archive of television programs;
• TV guide;
• cinema hall;
• availability of radio channels in the multiplex;
• reduction in transmitter power.

TV viewers can watch from 10 to 20 channels for free, enjoying high quality video and taking advantage of a number of other advantages of DTV . To get more TV channels, you will need to purchase a package from one of the TV operators.

The difference between a discrete signal and a digital one

Everyone has probably heard about Morse code. It was invented by the artist Samuel Morse, other innovators improved it, and used everything. This is a method of transmitting text where letters are encoded with dots and dashes. Simplified, the encoding is called Morse code. It was used for a long time in the telegraph and for transmitting information via radio. In addition, you can signal using a spotlight or flashlight.

The Morse code depends only on the sign itself. And not on its duration or volume (strength). No matter how you hit the key (blink a flashlight), only two options are perceived - a dot and a dash. You can only increase the transfer speed. Neither volume nor duration are taken into account. The main thing is that the signal gets through.

So is the digital signal.

It is important to encode the data using 0s and 1s. The recipient must only parse the combination of zeros and ones

It doesn’t matter how loud or how long each signal will be. It is important to get the ones and zeroes. This is the essence of digital technology.

A discrete signal will be obtained if you also encode the volume (brightness) and duration of each dot and dash, or 0 and 1. In this case, there are more encoding options, but there is also confusion. The volume and duration can be inaudible. This is the difference between digital and discrete signals. Digital is generated and perceived unambiguously, discretely with variations.

The main advantages of digital instruments over analogue ones

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Introduction

The purpose of this work is to consider the advantages of digital technology and their reasons.

Digital technologies, as such, rely on representing signals in discrete bands of analog levels rather than as a continuous spectrum. All levels within a band represent the same signal state.

Since the late 90s of the last century, it has been generally accepted that the future lies with digital technologies. In this work I will try to highlight the main reasons and theses of this point of view.

Analog signal

An analog signal is a data signal in which each of the representing parameters is described by a function of time and a continuous set of possible values. Such signals are described by continuous functions of time, which is why an analog signal is sometimes called a continuous signal.

The properties of analog signals largely reflect their continuity:

· The absence of clearly distinguishable discrete signal levels makes it impossible to apply the concept of information in the form as it is understood in digital technologies to describe it. The “amount of information” contained in one reading will be limited only by the dynamic range of the measuring instrument.

· No redundancy. From the continuity of the value space it follows that any noise introduced into the signal is indistinguishable from the signal itself and, therefore, the original amplitude cannot be restored. In fact, filtering is possible, for example, by frequency methods, if any additional information about the properties of this signal (in particular, the frequency band) is known.

Let's consider this type of signal using a simple example. During a conversation, our vocal cords emit a certain vibration of varying tonality (frequency) and volume (sound signal level). This vibration, having traveled a certain distance, enters the human ear, affecting there the so-called auditory membrane. This membrane begins to vibrate with the same frequency and strength of vibration that our sound cords emitted, with the only difference that the strength of vibration weakens somewhat due to overcoming the distance.

So, the transmission of voice speech from one person to another can be safely called analog signal transmission , and here's why.

The point here is that our vocal cords emit the same sound vibration that the human ear itself perceives (we hear what we say), that is, the transmitted and received sound signal has a similar pulse shape and the same frequency spectrum sound vibrations, or in other words, “analogous” sound vibration.

Now, let's look at a more complex example. And for this example, let’s take a simplified diagram of a telephone, that is, the telephone that people used long before the advent of cellular communications.

During a conversation, speech sound vibrations are transmitted to the sensitive membrane of the handset (microphone). Then, in the microphone, the sound signal is converted into electrical impulses, and then travels through wires to the second handset, in which, using an electromagnetic transducer (speaker or earphone), the electrical signal is converted back into a sound signal.

In the above example, again, “ analog ” signal conversion is used. That is, sound vibration has the same frequency as the frequency of the electrical impulse in the communication line, and also, sound and electrical impulses have a similar shape (that is, similar).

In the transmission of a television signal, the analogue radio-television signal itself has a rather complex pulse shape, as well as a fairly high frequency of this pulse, because it transmits both audio information and video over long distances.

Digital signal

A digital signal is a data signal in which each of the representing parameters is described by a discrete-time function and a finite set of possible values.

The signals are discrete electrical or light pulses. With this method, the entire capacity of the communication channel is used to transmit one signal. The digital signal uses the entire cable bandwidth. Bandwidth is the difference between the maximum and minimum frequency that can be transmitted over a cable. Each device on such networks sends data in both directions, and some can receive and transmit simultaneously. Narrowband systems transmit data as a digital signal of a single frequency.

A discrete digital signal is more difficult to transmit over long distances than an analog signal, so it is pre- modulated on the transmitter side and demodulated on the information receiver side. The use of algorithms for checking and restoring digital information in digital systems can significantly increase the reliability of information transmission.

It should be kept in mind that a real digital signal is analog in its physical nature. Due to noise and changes in the parameters of transmission lines, it has fluctuations in amplitude, phase/frequency of polarization. But this analog signal (pulse and discrete) is endowed with the properties of a number. As a result, it becomes possible to use numerical methods (computer processing) to process it.

As an example of a “digital signal” , let’s take the principle of transmitting information using the fairly well-known “Morse code”. For those who are not familiar with this type of transmission of text information, I will briefly explain the basic principle below.

Previously, when signal transmission over the air (using a radio signal) was just developing, the technical capabilities of transmitting and receiving equipment did not allow transmitting a speech signal over long distances. Therefore, instead of speech information, text information was used. Since the text consists of letters, these letters were transmitted using short and long pulses of a tonal electrical signal.

This transfer of text information was called transfer of information using Morse code.

The tone signal, due to its electrical properties, had a greater throughput than the speech signal, and as a result, the range of the transmitting and receiving equipment increased.

The units of information in such signal transmission were conventionally called “dot” and “dash”. A short tone meant a dot, and a long tone meant a dash. Here, each letter of the alphabet consisted of a specific set of dots and dashes. So, for example, the letter A was designated by the combination " .- " (dot-dash), and the letter B " -... " (dash-dot-dot-dot), and so on.

That is, the transmitted text was encoded using dots and dashes in the form of short and long segments of a tone signal. If the words “MORSE CODE” are expressed using dots and dashes, it will look like this:

The digital signal is based on a very similar principle of encoding information, only the units of information themselves are different.

Any digital signal consists of so-called “binary code”. Here, logical 0 (zero) and logical 1 (one) are used as units of information.

If we take an ordinary pocket flashlight as an example, then if you turn it on, it will seem to mean a logical one, and if you turn it off, it will mean a logical zero.

In digital electronic circuits, logical units of 1 and 0 are taken to be a certain level of electrical voltage in volts. So, for example, a logical one will mean 4.5 volts, and a logical zero will mean 0.5 volts. Naturally, for each type of digital microcircuit, the voltage values ​​of logical zero and one are different.

Any letter of the alphabet, as in the example with the Morse code described above, in digital form, will consist of a certain number of zeros and ones, arranged in a certain sequence, which in turn are included in packets of logical pulses. So, for example, the letter A will be one packet of impulses, and the letter B will be another packet, but in the letter B the sequence of zeros and ones will be different than in the letter A (that is, a different combination of the arrangement of zeros and ones).

In a digital code, you can encode almost any type of transmitted electrical signal (including analog), and it doesn’t matter whether it is a picture, video signal, audio signal, or text information, and you can transmit these types of signals almost simultaneously (in a single digital stream) .

Analog devices

With the advent of electricity, people had the opportunity to use equipment powered by current. Every day more and more new devices appeared, science developed, technology improved. Back then, all inventions were considered analog. The word “analog” meant that the device works by analogy with something. To make it clearer, let's consider a measuring device. Let's say you need to build a graph of measurements; the measurement data themselves are known. The instrument will first derive an equation from the known data that describes the behavior of the graph, and then attempt to construct the graph. It works by analogy with an equation and strictly obeys its laws. And how accurately the equation describes the graph is not important to the device. Thus, analog electronic devices are devices for amplifying and processing analog electrical signals, made on the basis of electronic devices. There are two large groups into which analog electronic devices can be classified:

· Amplifiers are devices that, using the energy of a power source, form a new signal that is in shape a more or less exact copy of the given one, but exceeds it in current, voltage or power.

· Amplifier-based devices are mainly converters of electrical signals and resistances.

Electrical signal converters (active analog signal processing devices) are made on the basis of amplifiers, either by directly using the latter with special feedback circuits, or by slightly modifying them. These include devices for summing, subtracting, logarithming, antilogarithming, filtering, detecting, multiplying, dividing, comparing, etc. Resistance converters are based on amplifiers with feedback. They can transform the magnitude, type, and nature of resistance. They are used in some signal processing devices. A special class consists of all kinds of generators and related devices.

Digital devices

Digital are measuring instruments that automatically generate discrete signals of measurement information and give readings in digital form. By discrete we mean signals whose values ​​are expressed by the number N of pulses. A system of rules for representing information using discrete signals is called a code. Discrete signals, unlike continuous ones, have only a finite number of values, determined by the selected code.

The main and mandatory functional units of electronic digital measuring instruments are analog-to-digital converters, in which the measured analogue, i.e. continuous in time, the physical quantity X is automatically converted into an equivalent digital code, as well as digital readout devices in which the received code signals N are converted into digital symbols of the decimal number system, convenient for visual perception. The digital form of presentation of the measurement result, compared to the analogue one, speeds up the reading and significantly reduces the likelihood of subjective errors. Since most digital measuring instruments contain preliminary analog converters designed to change the scale of the measured input value x or convert it to another value Y = f(x), more convenient for the chosen coding method, then in the general case the block diagram of the device is presented in the form of Fig. .

Block diagram of a digital measuring instrument

Modern digital instruments contain analog-to-digital converters capable of producing hundreds or more conversions per second, which makes it possible to record rapidly occurring physical processes and easily interface research objects with a computer. Digital devices are a new stage in the evolution of technology that operates on digital data.

For clarity, let's consider the same case - you need to build a graph based on given measurements. The device will not create an equation; it will divide the graph into small pieces, and based on the known data, calculate the coordinates for each piece. Then the device will plot each piece according to the obtained coordinates, and due to the fact that there are a huge number of such pieces, they will represent a continuous graph. This is how digital technology works.

The main advantages of digital instruments over analogue ones

A digital signal, due to its electrical properties (as in the example with a tone signal), has a greater information transmission capacity than an analog signal. Also, a digital signal can be transmitted over a greater distance than an analogue one, without reducing the quality of the transmitted signal. For example, a continuous audio signal transmitted as a sequence of 1s and 0s can be reconstructed without error, provided that the transmission noise was not sufficient to prevent identification of the 1s and 0s. An hour of music can be stored on a CD using about 6 billion binary digits. This is especially true in recent years, taking into account the enormous growth in transmitted information (increase in the number of television and radio channels, increase in the number of telephone subscribers, increase in the number of Internet users and the speed of Internet lines).

Storing information in digital systems is easier than in analogue ones. The noise immunity of digital systems allows data to be stored and retrieved without corruption. In an analog system, aging and wear can degrade the recorded information. In digital, as long as the overall interference does not exceed a certain level, information can be restored absolutely accurately.

Digital computer-controlled systems can be controlled using software, adding new features without replacing the hardware. Often this can be done without the involvement of the manufacturer by simply updating the software product. This feature allows you to quickly adapt to changing requirements. In addition, it is possible to use complex algorithms that are impossible in analogue systems or feasible, but only at very high costs.

When transmitting a digital television signal, the viewer will no longer see such a defect as “the image is snowy”, as was the case with an analog signal with poor reception. In the digital transmission of TV channels, the picture quality can only be good, or there will be no picture at all if the reception is poor (that is, either yes or no).

As for the digital transmission of telephone conversations, here, with good quality, both a whisper and a scream, both low and high tones, can be transmitted, and it does not matter at what distance the telephone subscribers are located.

Digital technology has always been superior to analog technology in accuracy. For example, let's compare analog and digital voice recorders. If you need to record voice information, a digital device will cope with the task better than an analog one. This will be noticeable in the recording quality. The fact is that an analog recorder does not reproduce information so accurately; noise will be mixed into the recording, while a digital recorder will filter out unnecessary noise, and accordingly the sound will be more believable.

Digital technology is smaller. The devices are built on microcircuits capable of performing addition and subtraction operations on numbers, hence their small size. Unlike analogue devices, data from modern devices can be quickly processed by computers. Of course, analogue data can also be placed in a computer, but it will first need to translate them into “its” digital language.

Digital technology is more economical and lasts longer. Microcircuits consume less energy and can work properly for a long time, while mechanical equipment will quickly fail.

Digital devices also boast:

· Small error. The accuracy of analog instruments is limited by the errors of the measuring transducers, the measuring mechanism itself, scale errors, etc.

· High performance (number of measurements per unit of time); When measuring time-varying quantities, performance plays an important role. If indicating priors do not require high speed, since the capabilities of the operator working with them are limited, then, on the contrary, the requirement of speed becomes important when processing information using computers, to which digital devices are often connected.

· Absence of subjective error in readings of the measurement result - subjective errors associated with the characteristics of human vision, due to parallax, due to the resolution of the eye.

Digital filter

Digital filter - in electronics, any filter that processes a digital signal in order to highlight and/or suppress certain frequencies of this signal. Unlike a digital filter, an analog filter deals with an analog signal; its properties are non-discrete ; accordingly, the transfer function depends on the internal properties of its constituent elements.

The advantages of digital filters over analog ones are:

· High accuracy (the accuracy of analog filters is limited by element tolerances).

· Stability (unlike an analog filter, the transfer function does not depend on the drift of the characteristics of the elements).

· Flexibility of configuration, ease of change.

· Compactness - an analog filter at a very low frequency (fractions of a hertz, for example) would require extremely bulky capacitors or inductors.

But there are also disadvantages:

· Difficulty working with high-frequency signals. The frequency band is limited by the Nyquist frequency, which is equal to half the signal sampling frequency. Therefore, analog filters are used for high-frequency signals, or, if there is no useful signal at high frequencies, they first suppress high-frequency components using an analog filter, then process the signal with a digital filter.

· Difficulty in real-time operation—computations must be completed within the sampling period.

· High accuracy and high speed signal processing requires not only a powerful processor, but also additional, possibly expensive, hardware in the form of high-precision and fast analog-to-digital converters.

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Which TV is more economical?

Analogue broadcasting is very practical. To use it, you just need a TV and a whip antenna. There are a lot of necessary antennas on the market of various sizes and qualities, which are very inexpensive in price.

Digital television requires additional equipment, such as an operator cable, satellite dish, tuner, Internet, etc. It doesn’t matter which signal reception method you choose, it will affect your wallet more noticeably than its analogue.

Analogue television is quite cheap and does not require additional costs or subscription fees. Digital broadcasting incurs financial costs in the form of purchasing a tuner, installing a satellite dish, or a subscription fee to the operator.

Attention. In order to watch channels in digital format, your TV must support this format. The TV must support DTS, EDTV, HDTV formats.

How analog and digital signals are transmitted

The main difference between an analog signal and a digital one is that the first is transmitted in a continuous stream, which is easily influenced by external factors that degrade the quality of the output image. The digital signal is discrete, or intermittent, which helps protect it from interference.

An electrical analog signal consists of three elements:

• video signal, which contains data on the brightness of the picture;
• a color subcarrier in which color data is encrypted;
• sound signal.

It can be broadcast via radio from terrestrial TV stations or via cable.

Important! It is worth noting that analogue cable channels will continue to operate, ATV broadcasting will stop only in the terrestrial broadcasting system.

To watch analog television, it is enough to have a TV to which a regular VHF antenna is connected via a coaxial cable.

A digital broadcast signal, or DTV, is compressed binary code. This technology allows for the transfer of large amounts of information. Thanks to this, TV viewers can choose from hundreds of channels. Today in Russia digital TV is broadcast in the DVB-T2 standard. In order to watch DTV, you need an antenna and a receiver that will decipher the encoded signal. This usually needs to be purchased separately, but most TVs made after 2013 have a built-in receiver.

Signal created in the image and likeness

We encounter analog signals all the time, and they can be most effectively demonstrated using a vinyl music record. On it the sound is recorded in the form of a winding groove.

The player needle running along it follows the contour and transmits its movements to the device that produces the sound. Previously, the gramophone used a bell for this purpose, which amplified the amplitude of vibrations and turned them into sound.

We can say that it was an analog signal in its pure form that was recorded on the record. And this brings us to the idea that it represents information about a wave process, the parameters of which are amplitude (loudness) and frequency (pitch).

Here I want to make a scientific digression.

Educated people know that sound and light, heat and UV radiation and radio signals are all waves of a certain frequency. By creating such oscillations, we obtain their analogue (or analog signal).

Let's continue to look at our vinyl record. We know that the gramophone is a thing of the century before last, and over time it turned into electrical equipment. What's added?

A piezoelectric crystal was placed near the needle, which, under the influence of mechanical vibrations, produced an electric current that could already be transmitted. Its voltage varied at the same frequency and amplitude as the sound track of the record. The crystal current was very small and required amplification.

The corresponding unit handled this processing perfectly. At the output we received a current with the same frequency response, but a proportionally increased amplitude, which corresponds to a higher voltage.

Such voltage is already capable of displacing the core in the electromagnetic coil of the speaker, causing its membrane to vibrate... That's right, with the same frequency and amplitude.

It turns out that the signal is called analog because it exactly repeats the parameters that should be transmitted. And we encounter it everywhere:

• you are reading the test now. It contains signal letters that are similar to certain sounds. And the words that you mentally pronounce at the same time are analogues of objects or actions;
• any painting, drawing or photograph is an analogue of what we see;
• The sound that is converted into radio waves by the FM receiver is also an analog signal.