Basic Concept
In modern communication technology, audio information refers to voice or music synthesized by a computer through a special equipment by a computer.
According to the representation of the media, there are three categories: voice, music and effect.
video information refers to an active or continuous image information, which is composed of a series of consecutive image screens, each screen being a frame, and the frame is a basic unit constituting video information. Video information has an important position in the information transmitted by the modern communication system. The information of human acceptance is about 70% from the visual, so I has an accurate, intuitive, specific vivid, efficient, wide application, high information capacity.
The sound is a physical phenomenon, and it is a psychological phenomenon. The human ear has the ability to distinguish the sound, tone and tone of tone, and can also distinguish the direction and depth of the sound and feel the sense of space and depth of depth. Usually the subjective feelings of the human ear to the sound, namely the loudness, tone, and tone referred to as the three elements of sound.
Hearing characteristics and audio signal
human auditory features
1 people feel strong for sound
< P> When the intensity of the sound signal is grown in accordance with the index rules, people will generally feel that the sound is uniformly enhanced, so that the sound will be taken to the log, it can correspond to the strong sense of sound. Therefore, the logarithm of sound homing or sound pressure valid value is usually indicated by the sound, called the sound intensity LI or the sound pressure level LP, and the unit is decibel.2 people feel the sensation of sound frequencies
The sensation of the sound frequency is characterized by the high low of the tone, and the sensation of the tone is raised when the frequency of the sound is rising according to the index law. .
3 human hearing frequency response characteristics
Human hearing has not only manifested as the high and low of tones, but also the strong sense of sound in the same conditions in the same conditions. Different, that is, the frequency response of human hearing is not flat.
4 Human hearing masking effect
The presence of a sound in the human auditory system will affect people's auditory ability to other sounds, so that a voice masks another sound ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Restore a technology for light images.
(1) Video Signal and Image Scan
The process of implementing optical images to video image signal transformation in video technology is usually done in the camera. When the camera is imaged in the photocandle layer of the camera device by the camera lens, the different points on the photodites differ from the number of light electrons that actually excited, causing different electrical conductors to produce different potential fluctuations, forming and lighting. Abstract electrical image. The electrical image must be scanned to form a video signal that can be processed and transmitted.
(2) Video signal spectrum characteristics
The video signal has the quasi-cycle characteristics of rows, fields, or frames. By spectral analysis of exquisite video signals: it is composed of a base wave, and each harmonic, the energy is symmetrically symmetrically contaminated on both sides of the harmonic of the row frequency at the frame rate. For the moving video signal, its spectrum is distributed in a clustered cluster-centricular consecutive comb pattern centered on the frequency and its harmonics. For actual video signals, the higher the number of harmonics, the greater the attenuation of the fundamental amplitude.
Victory Victory
The hardware of the information processing is mostly a digital logic circuit or a digital computer, so the video and audio information must be digitally processed. In order to transmit and process audio information in digital form, you must first maximize the video and audio information, including two aspects of content
audio information time discretization and image information spatial position;
The above process involves the sampling, quantization, and encoding of the audio signal.
For audio signals, the sample is discretizing the audio signal on the time axis. For video signals, the sample is discretted on the spatial position.
Visual -Video Compression Code
The data rate generated after the digitization of the audio frequency signal is quite large, the amount of data is large, and the data rate is as an example, its data rate is as high as an example. 216Mbit / s, in this case, in order to improve the new to utilization and more information under limited channel capacity, the viewing audio data must be compressed.
Theoretical foundation
In data compression technology, the information about the information created by Shannon has extremely important guiding significance for data compression. It gives the theoretical limit of data compression; On the one hand, the technical pathway of data compression is indicated.
Audio Compression Coding Technology
For different types of audio signals, its signal bandwidth is different, and with the increase in the sound quality of the audio signal, the signal frequency range gradually increases. The amount of data requested to describe the signal also increases, thereby processes the increase in data time and transmission, and the increase in capacity of these data.
(1) Audio signal compression code method
In general, the compression encoding of the audio signal mainly has the following Main type:
1 waveform code
2 parameter code
3 mixed code
(2) Different quality requirements Audio coding technology Select
1 phone quality audio compression code
2 Audio compression code for radio quality "
3 high-fidelity surround stereo Audio Compression Code
Video Compression Code
(1) Redundancy
of Video Information Internal and video sequence There is a lot of redundant information between adjacent images. Outside the general time and space redundancy, there is still a variety of redundant information in general image data, mainly:
1 information entropy redundancy
2 Structural redundancy
3 knowledge redundancy
4 visual redundancy
(2) Compression code
1 predict code
2 exchange code
3 with motion compensation Inter-block prediction code
4 with motion compensation inter-interpolated encoding
Value Value Category
Ordinary Phone and Intelligent Network Business
(1) Ordinary telephone service
ordinary call The business is the most popular communication business inventions and applications, which provide people's most basic point-to-voice communication function with the support of the telephone exchange network based on circuit switched principles.
(2) Intelligent Network Service
Smart Network is an additional network set on the telephone network of the program-controlled switch. It adopts a new "Control and Exchange Separation Separation" idea, and put the network in the network in the network intelligence in the network intelligence to a new feature, which is an additional network, an additional network. Network structure.
IP phone
IP phone is typically referred to as an Internet phone or a network phone, which utilizes a router / packet-switched IP data network for transmission.
(1) Key Technology of IP Phone
The working principle of IP phone is to make analog to digital conversion, encoding, compression, and packaging voice signals. Then via the Internet network, to the receiving end, the split, decodes, decodes, and digital-to-mode conversion are fixed, thereby restores the voice signal.
The key technique related to the IP phone call quality can be summarized as the following aspects:
1 Speech compression technology
2 odor noise suppression technology
3 echo cancellation technology
4 Speech jitter processing technology
5 Voice Priority Technology
6IP Packet Segmentation Technology
7VoIP Forward error correction technology
(2) IP phone call
usually, divide the IP telephone communication into: PC to PC, PC to Phone and Phone to Phone.
Radio and Television
Digital Video Broadcast
Video Broadcast Service