Audio Coding Part 4
Transmission encoding format
PCM encoding
PCM Pulse Code Modulation is short for Pulse Code Modulation. In the text above, we mentioned the general PCM workflow. We don’t need to care which calculation method is used in the final PCM encoding. We just need to know the advantages and disadvantages of the 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 CD can only hold 72 minutes of music information.
WAV format
This is an old audio file format, developed by Microsoft. WAV is a file format that complies with the RIFF (Resource Interchange File Format) specification. All WAVs have a file header that contains encoding parameters for the audio stream. WAV does not have strict rules for encoding 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 an example, because AVI and WAV are very similar in file structure, but AVI has one more video stream. There are many types of AVIs we have come into contact with, so we often need to install some decoders to watch some AVIs. DivX, which we have come into contact with a lot, is a type of video encoding. AVI can use DivX encoding to compress video streams, of course we can also use other code compression. Similarly, WAV can also use a variety of audio codecs to compress its audio stream, but we commonly use WAV whose audio stream is processed by PCM encoding, but this does not mean that WAV can only use PCM codec, it is also you can use MP3 codec. in WAV Just like 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. All audio programs can support it perfectly. Because it can meet higher sound quality requirements, WAV is also the preferred format for music creation and editing. Suitable for storing musical material. Therefore, WAV based on PCM encoding is used as an intermediate format, and is often used in the mutual conversion of other encodings, such as MP3 to WMA.
MP3 encoding
As the most popular audio compression format, MP3 is widely accepted by everyone. Various MP3-related software products emerge in a never-ending stream, and more hardware products start to support MP3 as well. Many VCD/DVD players that we can buy are compatible with MP3. , and there are more portable MP3 players, etc. Although several of the major music companies are extremely displeased with this open format, they cannot prevent the survival and spread of this compressed audio format. MP3 has been in development for 10 years and is short for MPEG (MPEG: Moving Picture Experts Group) Audio Layer-3, which is an encoding scheme derived from MPEG1. MP3 can achieve an incredible 12:1 compression ratio and still maintain basically audible sound quality. In the days when the hard drive was expensive, users quickly accepted MP3. With the popularity of the Internet, hundreds of millions of users accepted MP3. users At the beginning of the release of MP3 encoding technology, it was actually very imperfect. Due to a lack of research on sound and human hearing, almost all early mp3 encoders were crudely encoded and the sound quality was severely damaged. With the continuous introduction of new technologies, mp3 encoding technology has been improved over and over again, including two major technical improvements.
