An analog signal is a function of a continuous argument( time).If the schedule is periodically interrupted, as happens in a sequence of pulses, for example, they are already talking about a certain discreteness of the pack.
The history of the emergence of the term
If you read carefully, it is not written anywhere where the definition came from - analog. In the West, the term was used since the forties by computer professionals. It was during the Second World War that the first computer systems, called digital, appeared. And to distinguish 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 to light, and the world was playing with toys on the ZX-Spectrum, an emulator for devices today can be obtained on the Internet. The gameplay required extraordinary perseverance, skill and excellent reaction. On a par with the kids, they also collected boxes and beat enemy aliens and adults. Modern games are much inferior to the first birdies, captured for some time the minds of players.
Sound Recording and Telephony
By the early 80s pop music began to appear in electronic form. The musical telegraph was presented to the public in 1876, it did not gain recognition. Popular music likes the audience in the broad sense of the word. The telegraph was able to produce a single note, transmit to a distance, where it was reproduced by a speaker of a special design. And although the Beatles used the electronic organ to create Sergeant Pepper, the synthesizer came into use in the late 70s. A truly popular and digital tool was already in the mid-80s: remember Modern Talking. Earlier synthesizers were used on analog circuits, starting with Novachord in 1939.
So, the ordinary citizen didn’t have any need to distinguish between analog and digital technologies until the latter became firmly in use. The word analog has become public knowledge since the early 80s. Regarding the origin of the term, it is traditionally considered that the index is borrowed from telephony, later migrated to the sound recording. Analog oscillations are fed directly to the speaker, a voice is immediately heard. The signal is similar to human speech, becoming an electrical analog.
If you send a digital signal to a speaker, you will hear an indescribable cacophony of notes of different pitch. This “speech” is familiar to anyone who loaded software and games from a magnetic tape into the memory of a computer. It is not like a human, because it is 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 is entirely dependent on well-chosen parameters.
At the same time, the term appeared in sound recordings, where music and voice went directly from a microphone onto a tape. Magnetic recording has become an analogue of real artists. Vinyl records are like musicians and are still considered the best carrier for any compositions. Although show a limited lifespan. CDs now often contain digital sound decoded by the decoder. According to Wikipedia, the new era began in 1975( en.wikipedia.org /wiki/ History_of_sound_recording).
In an analog signal, the proportionality between voltage or current and response on a reproducing device is observed. The term is then considered derived from the Greek analogos. What does proportional mean? However, the comparison is similar to the above: the signal is similar to the voice reproduced by the speakers.
In addition, in the technique used to refer to analog signals a different term - continuous. What corresponds to the above definition.
As follows from the definition, an analog signal has infinite energy, not limited in time. Therefore, its parameters are averaged. For example, the 220 V present in the outlet is called the active value for a specified reason. Therefore, apply valid( averaged over a certain interval) values. It is already clear that the analogue signal of 50 Hz frequency is present in the socket.
When it comes to discreteness, apply final values. For example, when buying a stun gun, you need to make sure that the impact energy does not exceed the particular value measured in joules. Otherwise, there will be trouble with the use or during the inspection. Since, starting with a specific energy value, the electric shock machine is used only by special forces, with a fixed upper limit. Other - illegal in principle, can lead to death in the application.
The pulse energy is found by multiplying the current and voltage by the duration. And it shows the finiteness of the parameter for discrete signals. In the technique there are also digital sequences. From a discrete digital signal differs rigidly defined parameters:
- The presence of two specified states: 0 and 1.
- Machine bits 0 and 1 are added to the pre-defined and understandable words of the participants( assembly language).
Reciprocal Transformation of
Signals An additional definition of an analog signal is its apparent randomness, the absence of visible rules, or similarity with certain natural processes. For example, a sinusoid can describe the rotation of the earth around the sun. This is an analog signal. In the theory of circuits and signals, a sinusoid is represented by a rotating amplitude vector. And the phase of current and voltage is different - these are two different vectors, generating reactive processes. What is observed in inductors and capacitors.
From the definition it follows that the analog signal is easily converted to discrete. Any switching power supply unit cuts the input voltage from the outlet into packs. Consequently, it is engaged in the conversion of an analog signal with a frequency of 50 Hz into discrete ultrasound packs. Varying the cutting parameters, the power supply adjusts the output values to the requirements of the electrical load.
The reverse process takes place inside a radio wave receiver with an amplitude detector. After rectifying the signal on the diodes, pulses of various amplitudes are formed. Information is embedded in the envelope of such a signal, the line connecting the vertices of the premise. Converting discrete pulses into an analog value is a filter. The principle is based on the integration of energy: during the period of the presence of voltage, the charge of the capacitor increases, then, between the peaks, the current is formed due to the accumulated earlier electron supply. The resulting wave is fed to the low-frequency amplifier, later to the speakers, where the result is audible to others.
The digital signal is encoded differently. There, the amplitude of the pulse is embedded in the machine word. It consists of ones and zeros, decoding is required. The operation involved electronic devices: graphics card, software products. Everyone downloaded from the Internet K-Lite codecs, this is the case. The driver is engaged in decoding of a digital signal and conversion for output to the speakers and display.
No need to hurry with confusion when the adapter is called a 3-D accelerator and vice versa. The first only converts the filed signal. For example, there is always an adapter behind the DVI digital input. It only deals with the conversion of 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 has the right( but not the obligation) to contain an adapter, but the main task is complex calculations for the construction of three-dimensional images. This technique allows you to unload the CPU and speed up the work of a personal computer.
From analog to digital signal is converted to ADC.This happens programmatically or inside the chip. Separate systems combine both. The procedure begins with taking samples that fit inside a given area. Each transformed becomes a machine word containing the calculated figure. Then the readings are packed with parcels, it becomes possible to forward to other subscribers a complex system.
The discretization rules are normalized by the Kotelnikov theorem, which shows the maximum sampling frequency. More often, the counting is forbidden, since there is a loss of information. Simplistically, it is considered sufficient sixfold excess of the sampling frequency above the upper limit of the signal spectrum. A larger stock is considered an added advantage, ensuring good quality. Anyone has seen the audio sample rate indications. Usually the parameter is above 44 kHz. The reason are the characteristics of human hearing: the upper limit of the spectrum 10 kHz. Therefore, a 44 kHz sampling rate is enough for mediocre sound transmission.
The difference between a discrete and digital signal
Finally, people from the outside world usually perceive analog information. If the eye sees a flashing light, peripheral vision will catch the surrounding landscape. Therefore, the final effect is not seen as discrete. Of course, it is possible to try to create a different perception, but it is difficult and will be entirely artificial. The application of Morse code, which consists of points and dashes easily distinguishable against the background of noise, is based on this. Discrete taps of the telegraph key are difficult to confuse with natural signals, even in the presence of strong noise.
Likewise, digital lines are introduced in a technique to eliminate interference. Any video lover is trying to get a coded copy of the film in maximum resolution. Digital information is capable of being transmitted over long distances without the slightest distortion. Assistants are known on both sides of the rules for the formation of pre-agreed words. Occasionally, redundant information is inserted into the digital signal, allowing you to correct or notice errors. This eliminates the wrong perception.
More precisely, discrete signals are given by samples at certain points in time. It is clear that such a sequence in reality is not formed due to the fact that the front and the decline have a finite length. Impulse is not transmitted instantly. Therefore, the sequence spectrum is not considered discrete. Hence, the signal can not be called. In practice, there are two classes:
- Analog pulse signals - the spectrum of which is located by the Fourier transform, therefore, is continuous, at least in certain areas. The result of a voltage or current on a circuit is a convolution operation.
- Discrete pulse signals show a discrete spectrum, operations with them are carried out through discrete Fourier transforms. Consequently, a discrete convolution is used.
These clarifications are important for students who read that pulse signals are analog. Discrete received the name of the spectrum. The term analog is used to distinguish. Epithet continuous is applicable, as already mentioned above, and in connection with the characteristics of the spectrum.
Correction: the spectrum of an infinite sequence of pulses is considered to be strictly discrete only. For bundles, the harmonic components are always vague. Such a spectrum resembles a sequence of pulses modulated in amplitude.