Information signals. Analog signals. Discrete signals. Analog and digital signals

An analog signal is a function of a continuous argument (time). If the graph is periodically interrupted, as happens in a sequence of pulses, for example, we are already talking about a certain discreteness of the burst.

History of the term

Computer Engineering

If you look closely, it is not written anywhere where the definition came into the world - analog. In the West, the term has been used since the forties by computer professionals. It was during the Second World War that the first computer systems, called digital, appeared. And to differentiate, we had to come up with new epithets.

The concept of analog entered the world of household appliances only in the early 80s, when the first Intel processors came out, and the world was playing with toys on the ZX-Spectrum; today you can get an emulator for devices on the Internet. The gameplay required extraordinary perseverance, dexterity and excellent reaction. Along with children, adults also collected boxes and beat enemy aliens. Modern games are far inferior to the early birds that captured the minds of players for some time.

Sound recording and telephony

By the beginning of the 80s, pop music with electronic processing began to appear. The musical telegraph was presented to the public in 1876, but did not gain recognition. Popular music appeals to audiences in the broadest sense of the word. The telegraph was able to produce a single note and transmit it over a distance, where it was reproduced by a specially designed speaker. And although the Beatles used an electronic organ to create Sergeant Pepper, the synthesizer came into use in the late 70s. The instrument became truly popular and digital already in the mid-80s: remember Modern Talking. Previously, analog synthesizers had been used, starting with Novachord in 1939.

So, the average citizen did not have a need to distinguish between analog and digital technologies until the latter became firmly established in everyday life. The word analog has been in the public domain since the early 80s. As for the origin of the term, it is traditionally believed that the indicator was borrowed from telephony and later migrated to sound recording. Analog vibrations are directly fed to the speaker, and the voice is immediately heard. The signal is similar to human speech and becomes an electrical analogue.

If you apply a digital signal to the speaker, an indescribable cacophony of notes of different tones will be heard. This “speech” is familiar to anyone who has loaded programs and games from magnetic tape into computer memory. It doesn’t look like a human one, because it’s digital. As for the discrete signal, in the simplest systems it is fed directly to the speaker, which serves as an integrator. The success or failure of an enterprise depends entirely on correctly selected parameters.

At the same time, the term appeared in sound recording, where music and voice went directly from the microphone to tape. Magnetic recording has become an analogue of real artists. Vinyl records are like musicians and are still considered the best medium for any compositions. Although they show a limited service life. CDs now often contain digital audio that is decoded by a decoder. According to Wikipedia, the new era began in 1975 (en.wikipedia.org/wiki/History_of_sound_recording).

Electrical measurements

In an analog signal, there is a proportionality between the voltage or current and the response on the playback device. The term will then be considered to come from the Greek analogos. What does proportional mean? However, the comparison is similar to the one above: the signal is similar to a voice reproduced by speakers.

In addition, in technology another term is used to refer to analog signals – continuous. Which corresponds to the definition given above.

general information

Signal energy

As follows from the definition, an analog signal has infinite energy and is not limited in time. Therefore, its parameters are averaged. For example, 220 V present in the sockets is called the effective value for the specified reason. Therefore, effective (averaged over a certain interval) values ​​are used. It is already clear that the socket contains an analog signal with a frequency of 50 Hz.

When it comes to discreteness, finite values ​​are used. For example, when purchasing a stun gun, you need to make sure that the impact energy does not exceed a particular value measured in joules. Otherwise, there will be problems with use or inspection. Since, starting from a specific energy value, the stun gun is used only by special forces, with an established upper limit. Anything else is illegal in principle and can lead to death when used.

The pulse energy is found by multiplying the current and voltage by the duration. And this shows the finiteness of the parameter for discrete signals. Digital sequences are also found in technology. A digital signal differs from a discrete signal by rigidly specified parameters:

1. Duration.
2. Amplitude.
3. The presence of two specified states: 0 and 1.
4. Machine bits 0 and 1 are added into words that are pre-agreed and understandable to participants (assembly language).

Mutual signal conversion

An additional definition of an analog signal is its apparent randomness, the absence of visible rules, or its similarity to certain natural processes. For example, a sine wave can describe the rotation of the Earth around the Sun. This is an analog signal. In circuit and signal theory, a sinusoid is represented by a rotating amplitude vector. And the phase of current and voltage is different - these are two different vectors, giving rise to reactive processes. What is observed in inductors and capacitors.

From the definition it follows that an analog signal is easily converted into a discrete one. Any switching power supply cuts the input voltage from the outlet into bundles. Consequently, it is engaged in converting an analog signal with a frequency of 50 Hz into discrete ultrasonic bursts. By varying the cutting parameters, the power supply adjusts the output values ​​to the requirements of the electrical load.

Inside a radio wave receiver with an amplitude detector, the reverse process occurs. After the signal is rectified, pulses of various amplitudes are formed on the diodes. The information is contained in the envelope of such a signal, the line connecting the vertices of the parcel. The filter converts discrete pulses into analog values. The principle is based on the integration of energy: during the period of voltage presence, the charge of the capacitor increases, then, in the interval between peaks, the current is formed due to the previously accumulated supply of electrons. The resulting wave is fed to a bass amplifier, and later to speakers, where the result is heard by others.

The digital signal is encoded differently. There, the pulse amplitude is contained in the machine word. It consists of ones and zeros, decoding is required. The operation is carried out by electronic devices: graphics adapter, software products. Everyone downloaded K-Lite codecs from the Internet, this is the case. The driver is responsible for decoding the digital signal and converting it for output to speakers and display.

There is no need to rush into confusion when an adapter is called a 3-D accelerator and vice versa. The first one only converts the supplied signal. For example, there is always an adapter behind the DVI digital input. It only deals with converting numbers from ones and zeros for display on the screen matrix. Retrieves information about brightness and RGB pixel values. As for the 3D accelerator, the device may (but is not required) to contain an adapter, but the main task is complex calculations for constructing three-dimensional images. This technique allows you to relieve the central processor and speed up the operation of your personal computer.

The analog to digital signal is converted into an ADC. This happens in software or inside the chip. Some systems combine both methods. The procedure begins by taking samples that fit within a given area. Each, when transformed, becomes a machine word containing the calculated digit. Then the readings are packaged in parcels, making it possible to send them to other subscribers of the complex system.

The sampling rules are normalized by Kotelnikov’s theorem, which shows the maximum frequency of sampling. More often it is prohibited to take a countdown, since information is lost. To put it simply, a sixfold excess of the sampling frequency above the upper limit of the signal spectrum is considered sufficient. A larger supply is considered an additional advantage, guaranteeing good quality. Anyone has seen indications of the sampling rate of sound recordings. Typically the setting is above 44 kHz. The reason is the peculiarities of human hearing: the upper limit of the spectrum is 10 kHz. Therefore, a sampling frequency of 44 kHz is enough for mediocre sound transmission.

Difference between discrete and digital signal

Finally, a person usually perceives analogue information from the outside world. If the eye sees a flashing light, peripheral vision will capture the surrounding landscape. Consequently, the final effect does not appear to be discrete. Of course, it is possible to try to create a different perception, but this is difficult and will turn out to be entirely artificial. This is the basis for the use of Morse code, which consists of dots and dashes that are easily distinguishable against the background noise. The discrete strokes of a telegraph key are difficult to confuse with natural signals, even in the presence of strong noise.

Similarly, digital lines have been introduced in technology to eliminate interference. Any video lover is trying to get an encoded copy of the film in maximum resolution. Digital information can be transmitted over long distances without the slightest distortion. Rules known on both sides for the formation of pre-agreed words become assistants. Sometimes redundant information is embedded in a digital signal, allowing errors to be corrected or detected. This eliminates misperceptions.

Pulse signals

To be more precise, discrete signals are given by readings at certain points in time. It is clear that such a sequence is not formed in reality due to the fact that the rise and fall have a finite length. The impulse is not transmitted instantly. Therefore, the spectrum of the sequence is not considered discrete. This means that the signal cannot be called that. In practice, there are two classes:

1. Analog pulse signals - the spectrum of which is determined by the Fourier transform, therefore, continuous, at least in certain areas. The result of the action of voltage or current on a circuit is found by the convolution operation.
2. Discrete pulse signals also show a discrete spectrum; operations with them are carried out through discrete Fourier transforms. Therefore, discrete convolution is also used.

These clarifications are important for literati who have read that pulse signals can be analog. Discrete are named after the features of the spectrum. The term analog is used to differentiate. The epithet continuous is applicable, as already mentioned above, and in connection with the characteristics of the spectrum.

Clarification: only the spectrum of an infinite sequence of pulses is considered strictly discrete. For a pack, the harmonic components are always vague. Such a spectrum resembles a sequence of amplitude-modulated pulses.

When you deal with television and radio broadcasting, as well as modern types of communications, you often come across terms such as "analog signal" And "digital signal". For specialists there is no mystery in these words, but for ignorant people the difference between “digital” and “analogue” may be completely unknown. Meanwhile, there is a very significant difference.

When we talk about a signal, we usually mean electromagnetic oscillations that induce EMF and cause current fluctuations in the receiver antenna. Based on these vibrations, the receiving device - a TV, radio, walkie-talkie or cell phone - forms an “idea” about what image to display on the screen (if there is a video signal) and what sounds to accompany this video signal.

In any case, the signal from a radio station or cell phone tower can appear in either digital or analog form. After all, for example, sound itself is an analog signal. At a radio station, the sound received by the microphone is converted into the already mentioned electromagnetic waves. The higher the sound frequency, the higher the output oscillation frequency, and the louder the speaker speaks, the greater the amplitude.

The resulting electromagnetic oscillations, or waves, are propagated in space using a transmitting antenna. So that the airwaves are not clogged with low-frequency interference, and so that different radio stations have the opportunity to work in parallel without interfering with each other, the vibrations resulting from the influence of sound are summed up, that is, “superimposed” on other vibrations that have a constant frequency. The last frequency is usually called the “carrier”, and it is to its perception that we tune our radio receiver in order to “catch” the analog signal of the radio station.

The reverse process occurs in the receiver: the carrier frequency is separated, and the electromagnetic oscillations received by the antenna are converted into sound oscillations, and the familiar voice of the announcer is heard from the speaker.

Anything can happen during the transmission of an audio signal from the radio station to the receiver. Third-party interference may occur, frequency and amplitude may change, which, of course, will affect the sounds produced by the radio. Finally, both the transmitter and receiver themselves introduce some error during signal conversion. Therefore, the sound reproduced by an analog radio always has some distortion. The voice may be fully reproduced, despite the changes, but there will be hissing or even some wheezing in the background caused by interference. The less reliable the reception, the louder and more distinct these extraneous noise effects will be.

In addition, the terrestrial analog signal has a very weak degree of protection from unauthorized access. For public radio stations this, of course, makes no difference. But when using the first mobile phones, there was one unpleasant moment associated with the fact that almost any third-party radio receiver could easily be tuned to the desired wavelength to eavesdrop on your telephone conversation.

Analogue broadcasting has such disadvantages. Because of them, for example, television promises to become completely digital in a relatively short time.

Digital communications and broadcasting are considered more protected from interference and external influences. The thing is that when using “digital”, the analog signal from the microphone at the transmitting station is encrypted into a digital code. No, of course, a stream of figures and numbers does not spread into the surrounding space. Simply, a code of radio pulses is assigned to a sound of a certain frequency and volume. The duration and frequency of the pulses are preset - it is the same for both the transmitter and the receiver. The presence of an impulse corresponds to one, the absence - zero. Therefore, such communication is called “digital”.

A device that converts an analog signal into a digital code is called analog-to-digital converter (ADC). And the device installed in the receiver that converts the code into an analog signal corresponding to your friend’s voice in the speaker of a GSM cell phone is called a “digital-to-analog converter” (DAC).

During digital signal transmission, errors and distortions are virtually eliminated. If the impulse becomes a little stronger, longer, or vice versa, then it will still be recognized by the system as a unit. And zero will remain zero, even if some random weak signal appears in its place. For ADC and DAC there are no other values ​​like 0.2 or 0.9 - only zero and one. Therefore, interference has almost no effect on digital communications and broadcasting.

Moreover, “digital” is also more protected from unauthorized access. After all, in order for the device’s DAC to decrypt the signal, it must “know” the decryption code. The ADC, along with the signal, can also transmit the digital address of the device selected as the receiver. Thus, even if the radio signal is intercepted, it cannot be recognized due to the absence of at least part of the code. This is especially true.

So here you go differences between digital and analog signals:

1) An analog signal can be distorted by interference, and a digital signal can either be completely clogged with interference, or arrive without distortion. The digital signal is either definitely present or completely absent (either zero or one).

2) The analog signal is accessible to all devices operating on the same principle as the transmitter. The digital signal is securely protected by a code and is difficult to intercept if it is not intended for you.

Digital circuit design is the most important discipline that is studied in all higher and secondary educational institutions that train specialists in electronics. A real radio amateur should also be well versed in this issue. But most books and textbooks are written in a language that is very difficult to understand, and it will be difficult for a beginning electronics engineer (perhaps a school student) to learn new information. A series of new educational materials from Master Keith is designed to fill this gap: our articles explain complex concepts in the simplest terms.

8.1. Analog and digital signals

First you need to understand how analog circuitry differs from digital circuitry. And the main difference is in the signals with which these circuits work.
All signals can be divided into two main types: analog and digital.

Analog signals

Analog signals are the most familiar to us. We can say that the entire natural world around us is analog. Our vision and hearing, as well as all other senses, perceive incoming information in analog form, that is, continuously over time. Transmission of sound information - human speech, sounds of musical instruments, roars of animals, sounds of nature, etc. – also carried out in analog form.
To understand this issue even better, let’s draw an analog signal (Fig. 1):

Fig.1. Analog signal

We see that the analog signal is continuous in time and amplitude. For any moment in time, you can determine the exact value of the amplitude of the analog signal.

Digital signals

Let's analyze the signal amplitude not constantly, but discretely, at fixed intervals. For example, once per second, or more often: ten times per second. How often we do this is called the sampling rate: once per second - 1 Hz, a thousand times per second - 1000 Hz or 1 kHz.

For clarity, let’s draw graphs of analog (above) and digital (below) signals (Fig. 2.):

Fig.2. Analog signal (top) and its digital copy (bottom)

We see that at every instantaneous time interval we can find out the instantaneous digital value of the signal amplitude. We don’t know what happens to the signal (according to what law it changes, what is its amplitude) between the “check” intervals; this information is lost to us. The less often we check the signal level (the lower the sampling frequency), the less information we have about the signal. Of course, the opposite is also true: the higher the sampling rate, the better the quality of the signal presentation. In the limit, increasing the sampling frequency to infinity, we get almost the same analog signal.
Does this mean that an analog signal is in any case better than a digital one? In theory, perhaps, yes. But in practice, modern analog-to-digital converters (ADCs) operate with such a high sampling rate (up to several million samples per second) and describe the analog signal in digital form so qualitatively that the human senses (eyes, ears) can no longer sense the difference between original signal and its digital model. A digital signal has a very significant advantage: it is easier to transmit over wires or radio waves; interference does not have a significant effect on such a signal. Therefore, all modern mobile communications, television and radio broadcasting are digital.

The bottom graph in Fig. 2 is easy to imagine in another form - as a long sequence of a pair of numbers: time/amplitude. And numbers are exactly what digital circuits need. True, digital circuits prefer to work with numbers in a special representation, but we will talk about this in the next lesson.

Now we can draw important conclusions:

The digital signal is discrete, it can only be determined for individual moments in time;
- the higher the sampling frequency, the better the accuracy of the digital signal representation.

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.

There are two spaces of signals - the space L (continuous signals), and the space l (L small) - the space of sequences. The space l (L small) is the space of Fourier coefficients (a countable set of numbers that define a continuous function on a finite interval of the domain of definition), the space L is the space of continuous (analog) signals over the domain of definition. Under certain conditions, the space L is uniquely mapped into the space l (for example, the first two Kotelnikov discretization theorems).

Analog signals are described by continuous functions of time, which is why an analog signal is sometimes called a continuous signal. Analog signals are contrasted with discrete (quantized, digital). Examples of continuous spaces and corresponding physical quantities:

direct: electrical voltage

circle: position of a rotor, wheel, gear, analog clock hands, or phase of a carrier signal

segment: position of a piston, control lever, liquid thermometer or electrical signal limited in amplitude various multidimensional spaces: color, quadrature-modulated signal.

The properties of analog signals are largely the opposite of those of quantized or digital signals.

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.

Application:

Analog signals are often used to represent continuously changing physical quantities. For example, an analog electrical signal taken from a thermocouple carries information about temperature changes, a signal from a microphone carries information about rapid changes in pressure in a sound wave, etc.

2.2 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. A 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 (baseband) transmit data in the form of 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.

Comment. It should be kept in mind that a real digital signal is analog in its physical nature. Due to noise and changes in transmission line parameters, it has fluctuations in amplitude, phase/frequency (jitter), and 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.

The average person does not think about the nature of signals, but sometimes he does about the difference between analog and digital broadcasting or formats. 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 is worth knowing what we are giving up in favor of new trends.

Analog signal- a data signal described by continuous functions of time, that is, the amplitude of its oscillations 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 an analog signal is accompanied by a large amount of noise, while a digital signal successfully filters it 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 televisions and the demand for them is catastrophically decreasing.

Another important characteristic of a signal is security. 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. It is difficult to transmit digital signals over long distances, so 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.

A simple consumer does not need to know what the nature of the signals is. But sometimes it is necessary to know the difference between analog and digital formats in order to approach the choice of one option or another with open eyes, because today it is heard that the time of analog technologies has passed, they are being replaced by digital ones. You need to understand the difference so that you know what you are leaving behind and what to expect.

Signal analog- this is a continuous signal, having an infinite number of data close in value within the maximum, all parameters of which are described by a time dependent variable.

Digital signal- this is a separate signal described by a separate function of time; accordingly, at each moment in time, the amplitude of the signal has a strictly defined value.

Practice has shown that with analog signals interference is possible, which can be eliminated with a digital signal. In addition, digital can restore the original data. With a continuous analog signal, a lot of information passes through, often unnecessary. Instead of one analogue one, several digital ones can be transmitted.

Today, consumers are interested in the issue of television, since it is in this context that the phrase “switching to a digital signal” is often uttered. In this case, analog can be considered a relic of the past, but this is what the existing technology accepts, and to receive digital, a special one is needed. Of course, due to the emergence and expansion of the use of “digitals”, they are losing their former popularity.

Advantages and disadvantages of signal types

Safety plays an important role in assessing the parameters of a particular signal. Various types of influence, extraneous intrusions make the analog signal defenseless. With digital, this is excluded, since it is encoded from radio pulses. For long distances, the transmission of digital signals is complicated, and it is necessary to use modulation-demodulation schemes.

To sum it up, we can say that differences between analog and digital signals consist:

• In continuity of analog and discreteness of digital;
• There is a greater likelihood of interference during analog transmission;
• In analog signal redundancy;
• In the ability of the digital to filter noise and restore the original information;
• In the transmission of a digital signal in encoded form. One analog signal is replaced by several digital ones.

Very often we hear such definitions as “digital” or “discrete” signal; what is its difference from “analog”?

The essence of the difference is that the analog signal is continuous in time (blue line), while the digital signal consists of a limited set of coordinates (red dots). If we reduce everything to coordinates, then any segment of an analog signal consists of an infinite number of coordinates.

For a digital signal, the coordinates along the horizontal axis are located at regular intervals, in accordance with the sampling frequency. In the common Audio-CD format this is 44100 points per second. The vertical accuracy of the coordinate height corresponds to the bit depth of the digital signal; for 8 bits it is 256 levels, for 16 bits = 65536 and for 24 bits = 16777216 levels. The higher the bit depth (number of levels), the closer the vertical coordinates are to the original wave.

Analogue sources are: vinyl and audio cassettes. Digital sources are: CD-Audio, DVD-Audio, SA-CD (DSD) and files in WAVE and DSD formats (including derivatives of APE, Flac, Mp3, Ogg, etc.).

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.

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

Advantages and disadvantages of digital signal

The advantages of a digital signal include accuracy when copying and transmitting an audio stream, where the original is no different from the copy.

The main disadvantage is that the digital signal is an intermediate stage and the accuracy of the final analog signal will depend on how detailed and accurately the sound wave is described by coordinates. It is quite logical that the more points there are and the more accurate the coordinates are, the more accurate the wave will be. But there is still no consensus on what number of coordinates and the accuracy of the data is sufficient to say that the digital representation of the signal is sufficient to accurately restore the analog signal, indistinguishable from the original by our ears.

In terms of data volumes, the capacity of a regular analog audio cassette is only about 700-1.1 MB, while a regular CD holds 700 MB. This gives an idea of ​​the need for high capacity media. And this gives rise to a separate war of compromises with different requirements for the number of describing points and the accuracy of coordinates.

Today, it is considered quite sufficient to represent a sound wave with a sampling frequency of 44.1 kHz and a bit depth of 16 bits. At a sampling rate of 44.1 kHz, it is possible to reconstruct a signal up to 22 kHz. As psychoacoustic studies show, a further increase in the sampling frequency is not noticeable, but an increase in the bit depth gives a subjective improvement.

How DACs build a wave

A DAC is a digital-to-analog converter, an element that converts digital sound into analog. We will look superficially at the basic principles. If the comments indicate an interest in considering a number of points in more detail, a separate material will be released.

Multibit DACs

Very often, a wave is represented as steps, which is due to the architecture of the first generation of multi-bit R-2R DACs, which operate similarly to a relay switch.

The DAC input receives the value of the next vertical coordinate and at each clock cycle it switches the current (voltage) level to the appropriate level until the next change.

Although it is believed that the human ear can hear no higher than 20 kHz, and according to Nyquist theory it is possible to restore the signal to 22 kHz, the quality of this signal after restoration remains a question. In the high-frequency region, the resulting “stepped” waveform is usually far from the original one. The easiest way out of the situation is to increase the sampling rate when recording, but this leads to a significant and undesirable increase in file size.

An alternative is to artificially increase the DAC playback sampling rate by adding intermediate values. Those. we imagine a continuous wave path (gray dotted line) smoothly connecting the original coordinates (red dots) and add intermediate points on this line (dark purple).

When increasing the sampling frequency, it is usually necessary to increase the bit depth so that the coordinates are closer to the approximated wave.

Thanks to intermediate coordinates, it is possible to reduce the “steps” and build a wave closer to the original.

When you see a boost function from 44.1 to 192 kHz in a player or external DAC, it is a function of adding intermediate coordinates, not restoring or creating sound in the region above 20 kHz.

Initially, these were separate SRC chips before the DAC, which then migrated directly to the DAC chips themselves. Today you can find solutions where such a chip is added to modern DACs, this is done in order to provide an alternative to the built-in algorithms in the DAC and sometimes get even better sound (as for example, this is done in the Hidizs AP100).

The main refusal in the industry from multibit DACs occurred due to the impossibility of further technological development of quality indicators with current production technologies and the higher cost compared to “pulse” DACs with comparable characteristics. However, in Hi-End products, preference is often given to old multi-bit DACs rather than new solutions with technically better characteristics.

Switching DACs

At the end of the 70s, an alternative version of DACs based on a “pulse” architecture – “delta-sigma” – became widespread. Pulse DAC technology enabled the emergence of ultra-fast switches and allowed the use of high carrier frequencies.

The signal amplitude is the average value of the pulse amplitudes (pulses of equal amplitude are shown in green, and the resulting sound wave is shown in white).

For example, a sequence of eight cycles of five pulses will give an average amplitude (1+1+1+0+0+1+1+0)/8=0.625. The higher the carrier frequency, the more pulses are smoothed and a more accurate amplitude value is obtained. This made it possible to present the audio stream in one-bit form with a wide dynamic range.

Averaging can be done with a regular analog filter, and if such a set of pulses is applied directly to the speaker, then at the output we will get sound, and ultra high frequencies will not be reproduced due to the high inertia of the emitter. PWM amplifiers work on this principle in class D, where the energy density of pulses is created not by their number, but by the duration of each pulse (which is easier to implement, but cannot be described with a simple binary code).

A multibit DAC can be thought of as a printer capable of applying color using Pantone inks. Delta-Sigma is an inkjet printer with a limited range of colors, but due to the ability to apply very small dots (compared to an antler printer), it produces more shades due to the different density of dots per unit surface.

In an image, we usually do not see individual dots due to the low resolution of the eye, but only the average tone. Likewise, the ear does not hear impulses individually.

Ultimately, with current technologies in pulsed DACs, it is possible to obtain a wave close to what should theoretically be obtained when approximating intermediate coordinates.

It should be noted that after the advent of the delta-sigma DAC, the relevance of drawing a “digital wave” in steps disappeared, because This is how modern DACs do not build a wave in steps. It is correct to construct a discrete signal with dots connected by a smooth line.

Are switching DACs ideal?

But in practice, not everything is rosy, and there are a number of problems and limitations.

Because Since the overwhelming number of records are stored in a multi-bit signal, conversion to a pulse signal using the “bit to bit” principle requires an unnecessarily high carrier frequency, which modern DACs do not support.

The main function of modern pulse DACs is to convert a multi-bit signal into a single-bit signal with a relatively low carrier frequency with data decimation. Basically, it is these algorithms that determine the final sound quality of pulse DACs.

To reduce the problem of high carrier frequency, the audio stream is divided into several one-bit streams, where each stream is responsible for its own bit group, which is equivalent to a multiple of the carrier frequency of the number of streams. Such DACs are called multibit delta-sigma.

Today, pulsed DACs have received a second wind in high-speed general-purpose chips in products from NAD and Chord due to the ability to flexibly program conversion algorithms.

DSD format

After the widespread use of delta-sigma DACs, it was quite logical for the emergence of a format for recording binary code directly to delta-sigma encoding. This format is called DSD (Direct Stream Digital).

The format was not widely used for several reasons. Editing files in this format turned out to be unnecessarily limited: you cannot mix streams, adjust volume, or apply equalization. This means that without loss of quality, you can only archive analog recordings and produce two-microphone recording of live performances without further processing. In a word, you can’t really earn money.

In the fight against piracy, SA-CD format discs were not (and are still not) supported by computers, which makes it impossible to make copies of them. No copies – no wide audience. It was possible to play DSD audio content only from a separate SA-CD player from a proprietary disc. If for the PCM format there is an SPDIF standard for digital data transfer from a source to a separate DAC, then for the DSD format there is no standard and the first pirated copies of SA-CD discs were digitized from the analog outputs of SA-CD players (although the situation seems stupid, but in reality some recordings were released only on SA-CD, or the same recording on Audio-CD was deliberately made of poor quality to promote SA-CD).

The turning point occurred with the release of SONY game consoles, where the SA-CD disc was automatically copied to the console’s hard drive before playback. Fans of the DSD format took advantage of this. The appearance of pirated recordings stimulated the market to release separate DACs for playing DSD streams. Most external DACs with DSD support today support USB data transfer using the DoP format as a separate encoding of the digital signal via SPDIF.

Carrier frequencies for DSD are relatively small, 2.8 and 5.6 MHz, but this audio stream does not require any data reduction conversion and is quite competitive with high-resolution formats such as DVD-Audio.

There is no clear answer to the question of which is better, DSP or PCM. It all depends on the quality of implementation of a particular DAC and the talent of the sound engineer when recording the final file.

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 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.

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 is analogue 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 the analog signal, and therefore terrestrial television, is being carried out. 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 analog, there are still areas in which analog technology is indispensable, such as professional audio processing. 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 “analogue” and “digital” are types of terrestrial TV. Despite the fact that analogue television differs from digital television, their general principle of broadcasting is identical - a 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 propagate through highly oscillating waves, 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 a digital code contains virtually no errors or distortions. The device that digitizes the original signal is called an 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.

Digital TV	Analog TV
The digital image resolution is 1280x720, giving a total of 921600 pixels. In the case of the 1080i scan format, the image resolution is 1920x1080, which gives an impressive result: more than 2 million 70 thousand pixels.	The maximum resolution of an analog "picture" is approximately 720x480, which gives a total of more than 340,000 pixels.
Sound
Audio, like video, is transmitted without distortion. Many programs are accompanied by a surround stereo signal.	Sound quality varies.
Receiver
The cost of a TV adapted for digital reception is several times higher than the price of a regular TV.	Analog TV is moderately expensive.
TV channels
Watching digital channels gives the viewer a wide choice: a large number and thematic focus of TV channels.	Number of programs up to 100.
Other
Reception of programs on one TV. Additional services such as “private broadcast”, “virtual cinema”, “program storage”, etc.	Possibility of connecting more receivers and simultaneously viewing several programs.
Bottom line
The new television brings with it excellent picture and sound quality, the ability to create a multimedia home station for playing, working and learning. However, the high cost of adapted televisions and the slow introduction of TV encoding technology on the Russian market have so far left it behind existing television.	Good old TV is inferior to digital in image and sound quality. However, the price of the receivers and the ability to distribute the signal to a larger number of TVs (the ability to watch several programs at the same time) are a significant plus.

TV antenna sensitivity

There is no universal recipe for choosing the ideal antenna, but there are mandatory requirements that must be met in order for it to receive analog and digital signals. As the distance from the broadcast site 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.