The sound in nature is very complex, and the waveform is extremely complex. Usually we use pulse code modulation encoding, that is, PCM encoding. PCM converts continuously changing analog signals into digital codes through three steps: sampling, quantization and coding. At present, the application of audio coding has been very extensive, so what are the formats of audio coding? PCM pulse code modulation is the abbreviation of Pulse Code ModulaTIon. In the previous text, we mentioned the general workflow of PCM. We do not need to care about the calculation method used in the final encoding of PCM. We only need to know the advantages and disadvantages of PCM encoded audio stream. The biggest advantage of PCM encoding is good sound quality, and the biggest disadvantage is its large size. Our common Audio CD uses PCM encoding, and the capacity of one disc can only hold 72 minutes of music information. This is an ancient audio file format developed by Microsoft. WAV is a file format that complies with RIFF (Resource Interchange File Format) specifications. All WAVs have a file header, which contains the encoding parameters of the audio stream. WAV has no hard rules for the encoding of audio streams. In addition to PCM, almost all encodings that support the ACM specification can encode WAV audio streams. Many friends do not have this concept. Let ’s take AVI as a demonstration because AVI and WAV are very similar in file structure, but AVI has only one more video stream. There are many kinds of AVIs we come into contact with, so we often need to install some Decode to watch some AVIs. We are exposed to more DivX is a kind of video encoding, AVI can use DivX encoding to compress the video stream, of course, you can use other Encoding compression. Similarly, WAV can use a variety of audio encoding to compress its audio stream, but our common are WAV audio stream is processed by PCM encoding, but this does not mean that WAV can only use PCM encoding, MP3 encoding can also be used in WAV In the same way as AVI, as long as the corresponding Decode is installed, you can enjoy these WAVs. On the Windows platform, WAV based on PCM encoding is the best supported audio format, and all audio software can be perfectly supported. Since it can meet the requirements of higher sound quality, WAV is also the preferred format for music editing and creation. Suitable for saving music material. Therefore, WAV based on PCM encoding is used as an intermediary format, which is often used in the mutual conversion of other encodings, such as MP3 to WMA. As the most popular audio compression format, MP3 is widely accepted by everyone. Various software products related to MP3 have emerged in an endless stream, and more hardware products have begun to support MP3. Many VCD / DVD players we can buy are all Can support MP3, there are more portable MP3 players, etc., although several major music vendors are extremely disgusted with this open format, but can not stop the survival and spread of this audio compression format. MP3 has been in development for 10 years. He is the abbreviation of MPEG (MPEG: Moving Picture Experts Group) Audio Layer-3, which is a derivative encoding scheme of MPEG1. MP3 can achieve an astonishing compression ratio of 12: 1 and maintain basic audible sound quality. In the days when the hard disk was expensive, MP3 was quickly accepted by users. With the popularity of the network, MP3 was accepted by hundreds of millions of users. At the beginning of the release of MP3 encoding technology, it was actually very imperfect. Due to the lack of research on sound and human ear hearing, early mp3 encoders were almost all encoded in a crude manner, and the sound quality was seriously damaged. With the continuous introduction of new technologies, the mp3 encoding technology has been improved one at a time, including two major technical improvements. An audio encoding called Ogg Vorbis appeared on the Internet, known as the MP3 killer! What is the origin of Ogg Vorbis? OGG is the name of a huge multimedia development project, which will involve the development of video and audio coding. The purpose of the entire OGG project plan is to provide anyone with a completely free multimedia encoding scheme! OGG's belief is: OPEN! FREE! The word Vorbis is the name of a "playboy" in Terry Prattchat's fantasy novel "Small Gods". This vocabulary became the official name for audio coding in the OGG project. Currently Vorbis has been successfully developed, and an encoder has been developed. Ogg Vorbis is a high-quality audio encoding scheme. Official data shows that Ogg Vorbis can achieve better sound quality than MP3 at a relatively low data rate! The encoding of Ogg Vorbis is far more advanced than the MP3 developed in the 1990s. It can support multi-channel, what does it mean? This means that Ogg Vorbis can encode all channels with the support of SACD, DTSCD, DVD AUDIO ripping software (which is not currently available), instead of MP3, it can only encode 2 channels. The rise of multi-channel music has brought revolutionary changes to music appreciation, especially when you appreciate symphony, it will bring more sense of presence. MP3 cannot adapt to this revolutionary change. Like MP3, Ogg Vorbis is a flexible and open audio encoding, which can obviously adjust the sound quality and improve the new algorithm after the encoding scheme has been fixed. Therefore, its sound quality will be getting better and better, similar to MP3, Ogg Vorbis is more like an audio coding framework, you can continue to introduce new technologies and gradually improve. Like MP3, OGG also supports VBR. MPC is another impressive strength player. Its popularity is very low-key, and there is no complicated backstory. Her purpose is only one, smaller volume and better sound quality! MPC was formerly known as MP +, and obviously, it is possible to see who the competitor she is targeting. However, anyone who has used this encoding will have a deep impression of her superior sound quality. On June 14, 2001, Thomson MulTImedia SA and Fraunhofer InsTItute released a new music format version named mp3PRO on June 14. The improvement scheme based on mp3 encoding technology, from the officially announced features, does seem quite attractive. The data from all aspects shows that mp3PRO is not a brand-new format, which is completely an improvement based on the traditional mp3 encoding technology. The biggest technical highlight of itself is SBR (Spectral Band ReplicaTIon band replication), which is a new Audio coding enhancement algorithm. It offers the possibility to improve the performance of audio and speech coding at low bit rates. This method can increase the audio bandwidth or improve the coding efficiency at a specified bit rate. The biggest advantage of SBR is that it achieves very efficient encoding at low data rates. Unlike traditional encoding technologies, SBR is more like a post-processing technology, so the quality of the decoder's algorithm directly affects the quality of the sound quality. . The high frequency is actually generated by the decoder (player), and the SBR encoded data is more like a command set to generate high frequency, or a guiding signal source, which is a bit of the way idi works. We can see that mp3PRO is actually a mixed data stream encoding of mp3 signal stream and SBR signal stream. Relevant information shows that SBR technology can improve the high-frequency sound quality under low data traffic, the improvement is about 30%, we no matter how this 30% is obtained, but we can predict in advance that this improvement can make 64kbps mp3 to 128kbps The sound quality level of mp3 (note: under the same encoding conditions, the improvement of data rate and sound quality is not proportional to at least the human ear), which is comparable to the official claim of 64kbps mp3PRO comparable to 128kbps mp3 The propaganda is basically consistent. WMA is the file format after Windows Media Audio encoding, developed by Microsoft, WMA is not aimed at the stand-alone market, but the network! The competitor is the famous Real Networks in the online media market. Microsoft claims that at a bit rate of only 64kbps, WMA can achieve sound quality close to CD. Unlike the previous encoding, WMA supports anti-copy function. She supports adding protection through Windows Media Rights Manager, which can limit the playing time and playing times, even the playing machine and so on. WMA supports streaming technology, that is, reading while playing, so WMA can easily realize online broadcasting. Because it is a masterpiece of Microsoft, Microsoft has added support for WMA in Windows. WMA has excellent technical characteristics. Under the vigorous promotion, this format is accepted by more and more people. RA is the RealAudio format. This is a format that you all have a lot of contact with web worms. Most of the online auditions of music websites use RealAudio. This format is completely aimed at the media market on the Internet and supports very rich functions. The biggest flashing point is that this format can control its own code rate according to the bandwidth of the listener, and improve the sound quality as much as possible while ensuring smoothness. RA can support multiple audio encodings, including ATRAC3. Like WMA, RA not only supports reading while playing, but also supports the use of special protocols to hide the real network address of the file, so as to realize only online playback without providing a way to enjoy the download. This is very important for record companies and record sales companies. Under the vigorous promotion of all parties, RA and WMA are currently on the Internet, the audio media formats used for the most online listening. APE is a lossless compression format provided by Monkey's Audio. Monkey's Audio provides plug-in support for Winamp, so this means that the compressed file is no longer a simple compression format, but an audio file format that can be played like MP3. The compression ratio of this format is much lower than other formats, but it can be truly lossless, so it has won the favor of many enthusiast users. In many existing lossless compression schemes, APE is a format with outstanding performance, satisfactory compression ratio and fast compression speed, and has become the only choice for many friends to exchange fever music in private. Servo Cable is suitable for continuous moving occasions, double shielding effect strong anti-interference ability, signal transmission line and power connection line integration, saving installation space to reduce their own weight, maintain the reliability and stability of work, Widely used in control motors, executive motors, machine tool manufacturing, automobile manufacturing, heating and air conditioning systems, complete equipment installation engineering, paper industry, refrigeration equipment, office automation equipment, and data processing systems and other occasions. 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