Analog vs. digital signal bandwidth issues

Let's first say that the digital signal is the sampling of the analog signal and then the digital quantization, generally we use the digital bandwidth of 1Mbps is 125KB, and the bandwidth of the general TV signal is 8MHz. Well, the problem arises, these two are still not comparable, so look at it from another angle. It is the number of scan lines that determines the definition of TV, and it is not the TV set that determines the number of scan lines, but the TV system.

The system of analog TV in China adopts the PAL-D system, which stipulates that the number of image scanning lines is 625 lines, 50 lines, and 575 lines per frame.

If you achieve this clarity, the digital TV is 720 pixels, 576 pixels = 414720 pixels.

Generally, the PAL TV or video we watch is 25 frames per second.

If the digital compression method is not good, each pixel occupies one byte, then the digital bandwidth required to broadcast the PAL-D TV signal = 414720 pixels 25 = 10MB.

MPEG-2 was developed in 1994 with compression algorithms designed for high-level industry-standard image quality and higher transmission rates. MPEG-2 can provide transmission rates between 3 and 10Mbits, and its resolution can reach 720x486 in NTSC mode.

MPEG-2 is the most advanced compression standard, compressing the 720 576 resolution signal at 30 frames per second, suitable for computer display quality images, the compressed data rate is 6Mbps, it will be the **program**, audio, data content and other components are compounded into a single bit stream, so as to transmit the compression on the Internet or stored in the storage device. Only a small number of DVR products use the MPEG2 compression standard.

TV is only 480 lines,The clarity of the display is much worse,If you connect the **signal to the monitor,It will also be very unclear。 The broadband ** has also undergone great compression, the image quality has been seriously reduced, and it should be transmitted by the UDP protocol, and the files will inevitably be lost.

Analog signal bandwidth refers to the width of the analog signal spectrum, which is the difference between the highest frequency component and the lowest frequency component of the signal, and the analog channel bandwidth limits the lower and upper frequencies of the signal that are allowed to pass through the channel, that is, a frequency passband. The greater the frequency variation of the signal, the wider the bandwidth of the signal.

Analog signal refers to the information expressed by continuously changing physical quantities, such as temperature, humidity, pressure, length, current, voltage, etc., and the analog signal is called continuous signal, which can have an infinite number of different values within a certain time range.

The main advantage of analog signals is their precise resolution, and the information density of analog signals is higher. When the same effect is achieved, analog signal processing is simpler than digital signal processing. The processing of analog signals can be achieved directly through analog circuit components (e.g., operational amplifiers, etc.), while digital signal processing often involves complex algorithms and even requires specialized digital signal processors.

Electronics engineers teach you how to quickly recognize what an analog signal is and what a digital signal is!

The signal bandwidth is the width of the signal spectrum, that is, the difference between the highest frequency component and the lowest frequency component of the signal, for example, a square wave signal composed of several sine waves superimposed, the lowest frequency component is its fundamental frequency, assumed to be f

2kHz, its highest frequency component is its 7th harmonic frequency, i.e., 7f=7 2=14kHz, so this signal bandwidth is 7f-f=14-2=12kHz.

The channel bandwidth limits the lower and upper frequencies of the signal that are allowed to pass through the channel, that is, a frequency passband. For example, if a channel allows a passband of up to 15kHz and its bandwidth is 15kHz, all the frequency components of the above square wave signal can of course pass through the channel, and if the attenuation, delay and noise are not considered, the signal passing through this channel will not be distorted. However, if a square wave with a fundamental frequency of 1 kHz is passed, the distortion through that channel will certainly be severe; If the fundamental frequency of the square wave signal is 2khz, but the highest harmonic frequency is 18khz, the bandwidth exceeds the channel bandwidth, and the higher harmonics will be filtered out by the channel, and the square wave received through the channel is not sent; So, if the fundamental frequency of the square wave signal is 500Hz, the highest frequency component is the frequency of the 11th harmonic, and its bandwidth only needs to be 5kHz, which is much smaller than the channel bandwidth, can it pass through the channel well?

In fact, when the signal is transmitted on the channel, the fundamental frequency is filtered out, and only the harmonics can pass through, and the signal waveform must be unsightly.

There are many ways to classify signals, and signals can be divided into deterministic signals and non-deterministic signals (also known as random signals), continuous signals and discrete signals (i.e., analog signals) according to mathematical relationships, value characteristics, energy power, processing analysis, time function characteristics, and whether the value is a real number.

and digital signals), energy and power signals, time-domain signals, and frequency domains.

Signals, time-limited signals and frequency-limited signals, real signals and complex signals, etc.

Analog and digital signals.

Analog signal refers to the signal waveform that simulates the change of information and changes, and its main feature is that the amplitude is continuous, and an infinite number of values can be taken; In time, it can be continuous or discontinuous. This is shown in Figure 2.

A digital signal is a signal that is not only discrete in time, but also discrete in amplitude, and can only take a finite number of values in the virtual world. For example, telegraph signals, pulse code modulation (PCM) signals, etc. are all digital signals. Binary.

A signal is a digital signal, which is a combination of two digits, "1" and "0", to represent different information.

According to whether the communication system transmits analog signals or digital signals, the communication system is divided into analog communication system and digital communication system. If an analog signal is fed into the transmission system, this communication method is analog. Most of the ** and radio and television systems used today are analog communication methods.

If an analog signal is sampled, quantized, encoded, and converted into a digital signal and then transmitted, then this communication method is digital communication.

Compared with analog communication, although digital communication occupies a wide channel frequency band, it has the advantages of strong anti-interference ability, no noise accumulation, easy storage, processing and exchange, strong confidentiality, easy large-scale integration, and miniaturization, and is being widely used.

Analog signals and digital signals can be converted to each other: analog signals are generally quantized into digital signals by PCM pulse code modulation, that is, different amplitudes of analog signals correspond to different binary values, for example, 8-bit coding can be used to quantize analog signals into 2 8 = 256 orders of magnitude, and 24-bit or 30-bit coding is often used in practice; Digital signals are generally converted to analog signals by phase shifting the carrier. Computers, computer LANs.

Binary digital signals are used in the computer WAN with metro networks.

There are both binary digital signals and analog signals converted from digital signals. However, the more promising application development is the wild good digital signal.

One is a waveform and one is a number; One is the high and low level, and the other is 01010; One is coherent and one is disconnected; One is natural and the other is artificial.

Take audio recording and audio** as an example: 1When we speak, the voice is converted into a binary (0 1) signal that can be recognized by the computer through the microphone, and it is stored on the disk, and this stored file is in digital form; This kind of signal is a digital signal; Depending on the sampling frequency, the resulting audio file size will be different; High sampling frequency.

The digital signal represents 0,1**; Analog signals are represented by waveforms. Digital signals are discontinuous Analog signals are continuous Analog signals are continuous (amplitude can be expressed by an infinite number of values). Analog signals that are continuous in time and continuously change image (television, fax) signals, etc., and discrete analog signals in time are a type of sampling.

1. The working principle of the signal source is different.

Analog signals are signals that simulate changes in information (such as sound information, image information, etc.); Digital signals, on the other hand, are sampled, quantized, and encoded to form digital signals (also known as pulse signals).

2. Different output methods.

Analog signals are generally transmitted through traditional transmission lines (such as ** network, cable TV network). When a digital signal is represented by intermittent voltage or optical pulses, it is generally necessary to connect the two sides of the communication with twisted pair cables and optical fiber media to transmit signals from one node to another.

3. The signal status and mode are different.

A digital signal is a signal in which the independent variable is discrete and the dependent variable is also discrete, the independent variable of this signal is represented by an integer, and the dependent variable is represented by a number in a finite number. In computers, the magnitude of a digital signal is often expressed as a binary number with limited bits.

Analog communication characteristics: In order to improve the signal-to-noise ratio, it is necessary to amplify the attenuated transmission signal in time during signal transmission, and the noise that is inevitably superimposed on the signal during the transmission process is also amplified at the same time. As the transmission distance increases, the noise accumulates more and more, resulting in a serious deterioration of the transmission quality.

Manuscript Qi. Characteristics of digital communication: because the amplitude of the digital signal is a finite number of discrete values (usually two amplitudes), although it is also interfered by noise in the transmission process, when the signal-to-noise ratio deteriorates to a certain extent, the method of judgment regeneration is adopted at the appropriate distance, and then the same digital signal as the original transmitter is generated without noise interference, so long-distance high-quality transmission can be realized.