Differences between analog and digital sound. Analog, discrete, 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 unload 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 one, 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 loss occurs. 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 audio 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 characteristics 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.

Digital electronics are now increasingly replacing traditional analog electronics. Leading companies producing a wide variety of electronic equipment 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 of 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 advent of high-speed microprocessors, large-volume random access memory chips, and small-sized information storage devices 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 for recording and reproducing signals are also unthinkable without the use of 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, 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 primarily operate on electrical signals, although more recently light signals, which represent time-varying light intensity, have been increasingly used.

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 an acoustic system, are 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 the imperfection and imperfection of electronic devices. And when transmitted over long distances and during storage, the signals also weaken.

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 impossible to accurately calculate, 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 the aging of 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. The speed of processing and transmission of information by an 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 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.

A signal is defined as a voltage or current that can be transmitted as a message or as information. By their nature, all signals are analog, be it DC or AC, digital or pulse. However, it is common to make a distinction between analog and digital signals.

A digital signal is a signal that has been processed in a certain way and converted into numbers. Usually these digital signals are connected to real analog signals, but sometimes there is no connection between them. An example is data transmission over local area networks (LANs) or other high-speed networks.

In digital signal processing (DSP), the analog signal is converted into binary form by a device called an analog-to-digital converter (ADC). The ADC output produces a binary representation of the analog signal, which is then processed by an arithmetic digital signal processor (DSP). After processing, the information contained in the signal can be converted back to analog form using a digital-to-analog converter (DAC).

Another key concept in defining a signal is the fact that a signal always carries some information. This leads us to a key problem in physical analog signal processing: the problem of information retrieval.

Goals of signal processing.

The main purpose of signal processing is the need to obtain the information contained in them. This information is typically present in the signal amplitude (absolute or relative), frequency or spectral content, phase, or relative timing of multiple signals.

Once the desired information has been extracted from the signal, it can be used in a variety of ways. In some cases it is desirable to reformat the information contained in the signal.

In particular, a change in signal format occurs when transmitting an audio signal in a frequency division multiple access (FDMA) telephone system. In this case, analog methods are used to place multiple voice channels in the frequency spectrum for transmission via microwave radio relay, coaxial cable, or fiber optic cable.

In digital communication, analog audio information is first converted to digital using an ADC. Digital information representing individual audio channels is time multiplexed (time division multiple access, TDMA) and transmitted over a serial digital link (as in a PCM system).

Another reason for signal processing is to compress the signal bandwidth (without significant loss of information) followed by formatting and transmission of information at reduced speeds, which allows the required channel bandwidth to be narrowed. High-speed modems and adaptive pulse code modulation (ADPCM) systems widely use data redundancy elimination (compression) algorithms, as do digital mobile communications systems, MPEG audio recording systems, and high-definition television (HDTV).

Industrial data acquisition and control systems use information received from sensors to generate appropriate feedback signals, which in turn directly control the process. Please note that these systems require both ADC and DAC, as well as sensors, signal conditioners and DSPs (or microcontrollers).

In some cases, there is noise in the signal containing information and the main goal is to reconstruct the signal. Techniques like filtering, autocorrelation, convolution, etc. are often used to accomplish this task in both analog and digital domains.

Signal Conditioning

In most of the above situations (related to the use of DSP technologies), both an ADC and a DAC are required. However, in some cases, only a DAC is required when analog signals can be directly generated from the DSP and DAC. A good example is sweep video displays, in which a digitally generated signal drives the video image or RAMDAC (pixel array digital to analog converter) unit.

Another example is artificially synthesized music and speech. In reality, generating physical analog signals using digital-only methods relies on information previously obtained from sources of similar physical analog signals. In display systems, the data on the display must convey relevant information to the operator. When designing sound systems, the statistical properties of the generated sounds are specified, which have been previously determined through the extensive use of DSP methods (sound source, microphone, preamplifier, ADC, etc.).

Signal processing methods and technologies

Signals can be processed using analog techniques (analog signal processing, or ASP), digital techniques (digital signal processing, or DSP), or a combination of analog and digital techniques (mixed signal processing, or MSP). In some cases the choice of methods is clear, in other cases the choice is not clear and the final decision is based on certain considerations.

As for DSP, the main difference between it and traditional computer data analysis is the high speed and efficiency of complex digital processing functions such as filtering, analysis and real-time data compression.

The term "combined signal processing" implies that the system performs both analog and digital processing. Such a system can be implemented as a printed circuit board, a hybrid integrated circuit (IC), or a separate chip with integrated elements. ADCs and DACs are considered to be combined signal processing devices, since each of them implements both analog and digital functions.

Recent advances in Very High Level Integration (VLSI) IC technology enable complex (digital and analog) processing on a single chip. The very nature of the DSP means that these functions can be performed in real time.

Comparison of analog and digital signal processing

Today's engineer is faced with choosing the appropriate combination of analog and digital techniques to solve a signal processing problem. It is impossible to process physical analog signals using digital methods alone, since all sensors (microphones, thermocouples, piezoelectric crystals, disk drive heads, etc.) are analog devices.

Some types of signals require normalization circuits for further signal processing, both analogue and digital. Signal normalization circuits are analog processors that perform functions such as amplification, accumulation (in measuring and preliminary (buffer) amplifiers), signal detection against a background of noise (high-precision common mode amplifiers, equalizers and linear receivers), dynamic range compression (logarithmic amplifiers, logarithmic DACs and programmable gain amplifiers) and filtering (passive or active).

Several methods for implementing signal processing are shown in Figure 1. The top area of ​​the figure shows a purely analog approach. The remaining areas depict the DSP implementation. Note that once a DSP technology has been selected, the next decision must be to locate the ADC in the signal processing path.

ANALOG AND DIGITAL SIGNAL PROCESSING

Figure 1. Signal processing methods

In general, since the ADC is moved closer to the sensor, most of the analog signal processing is now done by the ADC. Increasing the capabilities of the ADC can be reflected in increasing the sampling rate, expanding the dynamic range, increasing the resolution, cutting off input noise, using input filtering and programmable amplifiers (PGA), the presence of on-chip voltage references, etc. All the mentioned additions increase the functional level and simplify the system.

With modern technologies available to produce DACs and ADCs with high sampling rates and resolutions, significant progress has been made in integrating more and more circuits directly into ADCs/DACs.

In the measurement industry, for example, there are 24-bit ADCs with built-in programmable amplifiers (PGAs) that allow full-scale 10 mV bridge signals to be digitized directly without subsequent normalization (eg the AD773x series).

At voice and audio frequencies, complex encoding-decoding devices are common - codecs (Analog Front End, AFE), which have an analog circuit built into the chip that meets the minimum requirements for external normalization components (AD1819B and AD73322).

There are also video codecs (AFE) for tasks such as CCD image processing and others (for example, the AD9814, AD9816, and AD984X series).

Implementation example

As an example of the use of DSP, compare analog and digital low-pass filters (LPFs), each with a cutoff frequency of 1 kHz.

The digital filter is implemented as a typical digital system, shown in Figure 2. Note that the diagram makes several implicit assumptions. First, in order to accurately process the signal, it is assumed that the ADC/DAC path has sufficient values ​​of sampling frequency, resolution and dynamic range. Secondly, in order to complete all its calculations within the sampling interval (1/f s), the DSP device must be fast enough. Thirdly, at the ADC input and DAC output there is still a need for analog filters for limiting and restoring the signal spectrum (anti-aliasing filter and anti-imaging filter), although the requirements for their performance are low. With these assumptions in place, digital and analog filters can be compared.

The required cutoff frequency for both filters is 1 kHz. Analog conversion is implemented of the first kind of sixth order (characterized by the presence of transmission coefficient ripples in the passband and the absence of ripples outside the passband). Its characteristics are presented in Figure 2. In practice, this filter can be represented by three second-order filters, each of which is built on an operational amplifier and several capacitors. Using modern computer-aided filter design (CAD) systems, creating a sixth-order filter is fairly easy, but meeting the 0.5 dB flatness specification requires precise component selection.

The 129-coefficient digital FIR filter shown in Figure 2 has a passband flatness of only 0.002 dB, a linear phase response, and a much steeper rolloff. In practice, such characteristics cannot be realized using analogue methods. Another obvious advantage of the circuit is that the digital filter does not require selection of components and is not subject to parameter drift, since the filter clock frequency is stabilized by a quartz resonator. A filter with 129 coefficients requires 129 multiply-accumulate (MAC) operations to calculate the output sample. These calculations must be completed within a 1/fs sampling interval to ensure real-time operation. In this example, the sampling rate is 10 kHz, so 100 μs of processing time is sufficient unless significant additional computation is required. The ADSP-21xx family of DSPs can complete the entire multiply-accumulate process (and other functions required to implement the filter) in a single instruction cycle. Therefore, a filter with 129 coefficients requires a speed of more than 129/100 μs = 1.3 million instructions per second (MIPS). Existing DSPs are much faster and thus are not the limiting factor for these applications. The 16-bit fixed-point ADSP-218x series delivers performance up to 75MIPS. Listing 1 shows the assembly code that implements the filter on DSP processors of the ADSP-21xx family. Note that the actual lines of executable code are marked with arrows; the rest is comments.

Figure 3. Analog and digital filters

Of course, in practice there are many other factors considered when comparing analog and digital filters or analog and digital signal processing methods in general. Modern signal processing systems combine analog and digital methods to implement the desired function and take advantage of the best methods, both analog and digital.

ASSEMBLY PROGRAM:
FIR FILTER FOR ADSP-21XX (SINGLE PRECISION)

MODULE fir_sub; ( FIR filter subroutine Subroutine call parameters I0 --> Oldest data in delay line I4 --> Start of filter coefficient table L0 = Filter length (N) L4 = Filter length (N) M1,M5 = 1 CNTR = Filter length - 1 (N-1) Return values ​​MR1 ​​= Result of summation (rounded and limited) I0 --> Oldest data in delay line I4 --> Start of filter coefficient table Variable registers MX0,MY0,MR Running time (N - 1) + 6 cycles = N + 5 cycles All coefficients are written in format 1.15).ENTRY fir; fir: MR=0, MX0=DM(I0,M1), MY0=PM(I4,M5) CNTR = N-1; DO convolution UNTIL CE; convolution: MR=MR+MX0*MY0(SS), MX0=DM(I0,M1), MY0=PM(I4,M5);

• MR=MR+MX0*MY0(RND);
  • IF MV SAT MR;
    • RTS; .ENDMOD;
  • REAL-TIME SIGNAL PROCESSING
  • Digital signal processing;
    • The spectrum width of the processed signal is limited by the sampling frequency of the ADC/DAC
• Remember the Nyquist criterion and Kotelnikov's theorem
  • limited by ADC/DAC capacity
  • DSP performance limits the amount of signal processing because:
  • For real-time operation, all calculations performed by the signal processor must be completed within a sampling interval equal to 1/f s

Don't forget about analog signal processing

high-pass/RF filtering, modulation, demodulation

analog limiting and spectrum restoring filters (usually low-pass filters) for ADCs and DACs

where common sense and cost of implementation dictate

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.

Every day people are faced with the use of electronic devices. Modern life is impossible without them. After all, we are talking about TV, radio, computer, telephone, multicooker and so on. Previously, just a few years ago, no one thought about what signal was used in each working device. Now the words “analog”, “digital”, “discrete” have been around for a long time. Some types of signals listed are of high quality and reliable.

Digital transmission came into use much later than analogue. This is due to the fact that such a signal is much easier to maintain, and the technology at that time was not so improved.

Every person encounters the concept of “discreteness” all the time. If you translate this word from Latin, it will mean “discontinuity.” Delving far into science, we can say that a discrete signal is a method of transmitting information, which implies a change in time of the carrier medium. The latter takes any value from all possible. Now discreteness is fading into the background, after the decision was made to produce systems on a chip. They are holistic, and all components closely interact with each other. In discreteness, everything is exactly the opposite - each detail is completed and connected to others through special communication lines.

Signal

A signal is a special code that is transmitted into space by one or more systems. This formulation is general.

In the field of information and communications, a signal is a special data carrier that is used to transmit messages. It can be created, but not accepted; the latter condition is not necessary. If the signal is a message, then “catching” it is considered necessary.

The described code is specified by a mathematical function. It characterizes all possible changes in parameters. In radio engineering theory, this model is considered basic. In it, noise was called an analogue of the signal. It represents a function of time that freely interacts with the transmitted code and distorts it.

The article describes the types of signals: discrete, analog and digital. The basic theory on the topic described is also briefly given.

Types of signals

There are several signals available. Let's look at what types there are.

1. According to the physical medium of the data carrier, electrical, optical, acoustic and electromagnetic signals are divided. There are several other species, but they are little known.
2. According to the method of setting, signals are divided into regular and irregular. The first are deterministic methods of data transmission, which are specified by an analytical function. Random ones are formulated using the theory of probability, and they also take on any values ​​at different periods of time.
3. Depending on the functions that describe all signal parameters, data transmission methods can be analog, discrete, digital (a method that is quantized in level). They are used to power many electrical appliances.

Now the reader knows all types of signal transmission. It won’t be difficult for anyone to understand them; the main thing is to think a little and remember the school physics course.

Why is the signal processed?

The signal is processed in order to transmit and receive information that is encrypted in it. Once it is extracted, it can be used in a variety of ways. In some situations it will be reformatted.

There is another reason for processing all the signals. It consists of a slight compression of frequencies (so as not to damage the information). After this, it is formatted and transmitted at slow speeds.

Analog and digital signals use special techniques. In particular, filtering, convolution, correlation. They are necessary to restore the signal if it is damaged or has noise.

Creation and formation

Often, an analog-to-digital converter (ADC) is needed to generate signals. Most often, both of them are used only in situations where DSP technologies are used. In other cases, only using a DAC will do.

When creating physical analog codes with the further use of digital methods, they rely on the information received, which is transmitted from special devices.

Dynamic range

It is calculated by the difference between the higher and lower volume levels, which are expressed in decibels. It completely depends on the work and the characteristics of the performance. We are talking about both musical tracks and ordinary dialogues between people. If we take, for example, an announcer who reads the news, then his dynamic range fluctuates around 25-30 dB. And while reading any work, it can rise to 50 dB.

Analog signal

An analog signal is a time-continuous method of data transmission. Its disadvantage is the presence of noise, which sometimes leads to a complete loss of information. Very often situations arise that it is impossible to determine where the important data is in the code and where there are ordinary distortions.

It is because of this that digital signal processing has gained great popularity and is gradually replacing analog.

Digital signal

A digital signal is special; it is described by discrete functions. Its amplitude can take on a certain value from those already specified. If an analog signal is capable of arriving with a huge amount of noise, then a digital signal filters out most of the received noise.

In addition, this type of data transmission transfers information without unnecessary semantic load. Several codes can be sent at once through one physical channel.

There are no types of digital signal, since it stands out as a separate and independent method of data transmission. It represents a binary stream. Nowadays, this signal is considered the most popular. This is due to ease of use.

Application of digital signal

How does a digital electrical signal differ from others? The fact that he is capable of performing complete regeneration in the repeater. When a signal with the slightest interference arrives at a communication equipment, it immediately changes its form to digital. This allows, for example, a television tower to generate a signal again, but without the noise effect.

If the code arrives with large distortions, then, unfortunately, it cannot be restored. If we take analog communications in comparison, then in a similar situation a repeater can extract part of the data, spending a lot of energy.

When discussing cellular communications of different formats, if there is strong distortion on a digital line, it is almost impossible to talk, since words or entire phrases are not audible. In this case, analog communication is more effective, because you can continue to conduct a dialogue.

It is precisely because of such problems that repeaters form a digital signal very often in order to reduce the gap in the communication line.

Discrete signal

Nowadays, every person uses a mobile phone or some kind of “dialer” on their computer. One of the tasks of devices or software is to transmit a signal, in this case a voice stream. To carry a continuous wave, a channel is required that has the highest level of throughput. That is why the decision was made to use a discrete signal. It does not create the wave itself, but its digital appearance. Why? Because the transmission comes from technology (for example, a telephone or computer). What are the advantages of this type of information transfer? With its help, the total amount of transmitted data is reduced, and batch sending is also easier to organize.

The concept of “sampling” has long been steadily used in the work of computer technology. Thanks to this signal, not continuous information is transmitted, which is completely encoded with special symbols and letters, but data collected in special blocks. They are separate and complete particles. This encoding method has long been relegated to the background, but has not disappeared completely. It can be used to easily transmit small pieces of information.

Comparison of digital and analog signals

When buying equipment, hardly anyone thinks about what types of signals are used in this or that device, and even more so about their environment and nature. But sometimes you still have to understand the concepts.

It has long been clear that analog technologies are losing demand, because their use is irrational. In return comes digital communication. We need to understand what we are talking about and what humanity is refusing.

In short, an analog signal is a method of transmitting information that involves describing data in continuous functions of time. In fact, speaking specifically, the amplitude of oscillations can be equal to any value within certain limits.

Digital signal processing is described by discrete time functions. In other words, the amplitude of oscillations of this method is equal to strictly specified values.

Moving from theory to practice, it must be said that the analog signal is characterized by interference. There are no such problems with digital, because it successfully “smoothes” them out. Thanks to new technologies, this method of data transfer is capable of restoring all the original information on its own without the intervention of a scientist.

Speaking about television, we can already say with confidence: analogue transmission has long outlived its usefulness. Most consumers are switching to a digital signal. The disadvantage of the latter is that while any device can receive analog transmission, a more modern method requires only special equipment. Although the demand for the outdated method has long fallen, these types of signals are still not able to completely disappear from everyday life.