One. Technical principle
1. The appearance of digital audio format in audio format is to meet the needs of replication, storage, and transmission. Simply put, early analog audio formats, there is a problem with replication distortion and due to dielectric wear. Starting from the storage of the CD disk, digital format audio files begin to popularize, but there is a problem - a restriction on the storage volume, while the CD disk still has a wear, if saved on the hard disk (longer storage time), When the storage medium (mainly hard drive) is still expensive, it is not a good solution. The emergence of the Internet has produced a long-distance transmission file. Under the restriction of bandwidth, the demand for narrowing the volume of the file has become more intense, which has caused damage to the digital audio format from external factors! From internal factors, with the improvement of computer operations, encoding ability, advances in various acoustic psychological models have promoted various layers of lossy compression digital audio formats. If the light from history and the coding format that have emerged now, there should be a lot, and the audio format used on MP3 machines, we introduce you to the following - MP3 (CBR, VBR, ABR) , WMA, ADPCM.
(1) MP3 (CBR, VBR, ABR) MP3 should be calculated using the most damaged compressed digital audio format of users using users. Its full name is MPEG (MPEG: MOVING PICTURE EXPERTS Group) Audio Layer-3, 1993, with the German Flang and Fisheries and the French Tomsheng company. It is not perfect when it appears, it is more like a code standard framework and leaves people to improve. The early MP3 encoding is a fixed coding rate (CBR), we often see 128kbps, which means it is fixed by 128kbps fixed data rate coding - you can improve this coding rate, up to 320kbps, sound quality Better, natural, the volume of the document will increase accordingly. Because the MP3 encoding method is open, you can choose different acoustic principles on this standard framework, so it is quickly launched a variable coded compression mode (VBR) that is expressed by Xing. Its principle is to use the complex part of a song with a high bitrate code, the simple part uses low bitrate encoding, in this way, further quality and volume unity. Of course, the early XING encoder's VBR algorithm is very poor, and the sound quality is far from the CBR (fixed code rate). However, this algorithm indicates a direction, and other developers have launched their own VBR algorithms that make the effect have been improved. It is currently recognized that the first push Lame is perfectly implemented, and it is a completely free software, and the development team consisting of enthusiasts has been constantly developing. On the basis of VBR, LAME has developed ABR algorithm. Average Bitrate The average bit rate is an interpolation parameter of VBR. LAME has created this encoding mode for the poor file volume ratio of CBR and the size of VBR generated files. ABR is in the specified file size, with a relatively low flow rate, high-frequency and non-active frequencies, using high traffic, high-frequency, and high-frequency performance, can be used as VBR and CBR A compromise choice. (2) WMA WMA is the abbreviation of Windows Media Audio, which is the digital music format pushed by Microsoft. Microsoft officially announced the information referred to in the WMA format and can even qualify the number of players, play time, and playback, with considerable copyright protection capabilities. It should be said that WMA's launch is for the shortcomings of MP3 without copyright restrictions - ordinary users may welcome this format, but as a copy of the copyright owner, they prefer to have difficulty copying music compression technology, Microsoft's WMA takes care of these record companies, and it is foreseeable that the record industry may fully support the WMA standard. In addition to copyright protection, WMA is still deepening over the compression ratio. Its goal is to be smaller in the same sound quality conditions (of course, only in the case of MP3 below 192 kbps code rate, actually uses When the LAME algorithm compresses the MP3 format, the general reflection of the MP3 is better than WMA when the MP3 is known. Anyway, Microsoft wants to intervene, it can always rely on its own power and the monopoly on the software, it wanted to get what it wants (although it is not always the best) - this war It should be a Microsoft's other IE and Netscape for Netscape in the field of digital audio format.
Summary: Because the purpose of this article is written for the digital audio format used on the MP3, I only introduce two formats commonly used on MP3 in play format: MP3 and WMA. If you are from a digital audio format, in addition to the two formats mentioned, there are many other formats: RA, MIDI, VQF, ATRAC, ATRAC3, VORBIS, AIF / AIFF, MP3PRO, OGG, DOLBY®PRO Logic®, Dolby Digital 5.1, QDesign QDX, ATRAC3, Voiceage, and more. In fact, with the enhancement of computer computing ability, the progress of acoustic principles, the development of compression technology, will also have more digital compressed audio formats - compared to the MP3, WMA mentioned above, they or from compression than upper and lower workfarers Or from the copyright protection of the workmanship (with positive and reverse hits, some should not be), or from the sound quality. However, please note: The advanced technology of the format does not represent the market! A format is popular, and even a quantity of use, in addition to technical factors, it also depends on other factors. As far as my personal opinion, the first influence is very big, in MP3, it is because it is currently the largest size, so it has a shortcoming of its compression ratio, sound quality, copyright protection, but the user is very It is easy to form a inertia - the easier it is to get the MP3 file, the more users join this ranks; in turn, promote more files, using this format storage - this forms a forward loop, plus because more play software Support MP3, more third-party development more advanced coding algorithms, these all push MP3 in their own format, but also lead to more popularization in the user's use (as in that variety of formats I mentioned above, readers don't say It has been used or understanding, and some of some formats have you hear any questions). So, in the short term, I am in the development of MP3 format - except for the non-technical factors mentioned above, as the storage medium capacity and the network bandwidth increase, the compression ratio may become less important (I am now Dare boldly uses higher than 192kbps code rate to compress your CD, encounter classics, I even use 320kbps directly, the reason is nothing, my computer hard disk is 40g, and this configuration is still gradually, the copyright protection is also double-blade. Sword, a good thing for the manufacturer, and it is the psychological of the user. Therefore, in this chapter, I don't do MP3, WMA format comparison with other formats, only in these two current formats on MP3 machines. Comparison. From a compression ratio perspective, WMA can obtain a smaller volume-orte half of the MP3 file under the same sound quality under conditions below 192 kbps. So if your MP3 capacity is not big, and you don't pursue the more perfect sound quality (especially when your use is listening to some English textbooks, cross talk, the review book is not required, when the playback effect), if your MP3 machine Support for WMA format play, congratulations - your MP3 machine capacity can be doubled. Conversely, if your MP3 capacity is large enough (the current mainstream should be developed to 128m), but also pay attention to the sound quality, so strongly, you use the LAME compression algorithm, the average of 192kbps above the rate compression, you will find, you often Different feelings (of course, also related to the sound quality of the MP3 machine, the sound quality of the MP3 machine) is used. These are the feelings you have learned from my personal use, you can refer to.
But more important is to try it yourself - because the MP3 machine is getting more and more development - high, medium, low-end MP3 level thin partition: quality, function, price, only with yourself The model, through practice, can find the format and coding rate suitable for you. II. Application skills
1. Production of audio format files in audio format, should include two scope: 1 is from lossless compressed files (generally WAV format, and before this is generally captured from CD, DVD, other MPEG-4 format WAV format) Convert to MP3 or WMA format; 2 is the mutual conversion of these two formats and other format files (mainly RM, ADPCM) to both formats. When talking about these, it is actually the use of common software - through the corresponding software, we can achieve our goal, so this chapter is a basic operation of the specific common software after the introduction of the basic principles. (1) WAV format crawling (talking about the fidelity of CD-raging) WAV format as a lossless compression format, can be said to be a basic way to convert to other formats. Through special grab software, the audio is saved in WAV format. There are many software that achieve this purpose, and we are explained as an popular EAC as an example. Before using EAC, you must first tell you to pay attention to a few questions: 1. Quality of CD. This makes many friends don't pay attention, thinking that CD is the best sound quality, in fact, different CDs, because of material, production process, protection (wear), has a big impact on the final result. 2. Problem of the CD-ROM. Now the speed of the optical drive is getting faster, but it is reflected to grab the track, it is better to be better, and the author has used different optical drives. The impact on the results is very large (not light crawling speed, There is also the final result). So good grab software, let you have a lot of questions through your own settings in these two sides. (The following uses EAC V0.9 Beta 4 Chinese version to open the EAC, after the main interface, first click on "EAC" above the upper menu, select the "Extraction" section in the EAC Options in the EAC Options, there are several Options should pay attention: 1. "Displacement samples with mute filled": Recommended. This will supplement in mute when there is lost data, prevent noise; 2. "CRC calculation does not use empty sampling": The last choice This item is not selected. 3. "Synchronization between the track": It is recommended to choose. The purpose is to perform jitter and synchronous correction at the bonding of the track to avoid popping or pauses at the end and rear track. 4. "Error Recovery Quality": There are three options in high, medium and low. The higher the quality of the error correction, the better, of course, the speed is relatively slow. Playing a CD into your CD-ROM, the content of the quick CD appears on the main interface. At this point you can set the drive according to your own CD-ROM. Next is the second option "Drive Option" of the above menu: Recommend "Safe Mode", and "Drive Equipped with Exact FREs" under the project, "Drive can buffer audio data". After these effects have completed the quality of the grab, it can start to grab the track (strongly recommended to separate the grab and compression, so that the track can be skipped directly, so as not to affect the overall progress). The operation of the grab is very simple. After setting the storage directory, click the "WAV" option in the left shortcut bar to automatically capture all the tracks of the CD and save it into a WAV format (of course, you can also choose I want to catch a particular audio track that I want to catch). EAC will give a grab report after the end, if there is no problem, it will display smoothly, no error occurred. (2) On the basis of the non-destructive format WAV made above, we can start making MP3 and WMA files, first talk about MP3 files. It is a famous Lame here.
Lame is the abbreviation of Lame ain't an MP3 Encoder, which should be one of the best encoders that are currently making MP3 formats. Common Lame EXE format is a DOS application, which should have a certain difficulty for ordinary users. Therefore, there are many lacks of Lame on the Internet (you can call Lame through our familiar WIN window. Combine general users' habits), relatively well-known Lamer, Razorlame, WinLame, here you want to introduce the EAC in which we mentioned above, you can easily achieve from grabbing to compression. EAC You first do some settings before calling Lame: Open the "Compressed Options" of the "EAC" option, select "External Compression" in the window you jump out. There are several places we need to set: 1. "Use external programs": Of course you have to choose. "Lame MP3 Encoder" found in "Parameter Usage". Then "the path where the program is used to compress", by "Browse" by the right, pressing the location of the LAME. 2. "Added Command Row Options": This is the key. If you fill in, the "bit rate" below is ignored, and the command here is the guideline. So how do you fill in the command option? The advantage of the shell is to instead of complex DOS, instead of the complex DOS command: VBR format: High quality (slow): - Alt-Preset Extreme (Bitrates 220-270 kbit / s - usually at 256kbps) Fast ( Slightly a slightly poor quality than above): - Alt-Preset Fast Extreme (Same as above) High quality (slower): - Alt-Preset Standard (Note: Bitrates 180-220 Kbit / s - usually around 192 kbps) fast (slightly poor quality than above): - Alt-Preset Fast Standard (Bitrates is slightly poor than the above) Alt-Preset Extreme (Bitrates 220-270 kbit / s Usually at 256kbps) 3. CBR Format: If you select CBR format compression, "Added Command Row Options" does not fill, through "bit rate", select different compression ratios from 96-320kbps. After setting it, you can start compression, we are compressed from the WAV format, so select "Tools" in the menu - "Compressed WAV Format", select the WAV file to be compressed in the browser that is jumped (support Multiple selection, "OK" after the selection is complete, ok, sit down and take a break, soon our own quasi-Hi-Fi level MP3 will appear in your pre-set directory. (3) Production of WMA files
Microsoft's Windows Media Player begins with version 8.0, supports converting files in CD and WAV format into WMA format. However, considering copyright protection and the user of the 8.0 version is not too much, we will not introduce WMP8.0 production WMA, will be introduced to third-party software: Advanced WMA Workshop. Advanced WMA Workshop (hereinafter referred to as AWW) is a quite good music file conversion tool that can be easily converted between WMA, MP3, OGG VORBIS, and WAV formats, but also supports direct CD track directly It can also edit ID3V2TAGS and provide batch conversion functionality in WMA format. Its use interface is simple (I use the Chinese version), select the WAV file you want to convert in the specific file list on the right side of the intermediate window, then select "Go to WMA" in the four options in the upper right corner, then click on the above The shortcut button "Convert" will jump out of a window, set directly to save the directory, sampling rate, compression ratio, after the "OK" is "OK", soon automatically complete the conversion work. 2. Mutual conversion in audio format
In addition to the CD format, WAV, MP3, WMA files mentioned above, there is a popular music format RM on the Internet, which is the streaming of the stream of the REAL (also on video) because it is smaller, so Some applications that are not high in sound quality (I have some of my hands in this format), so the MP3 that is used to convert this format into MP3 functions, and WMA format is also a case where everyone is likely to be encountered. In fact, this conversion, the most basic idea is to turn into WAV format, and then the MP3, WMA method mentioned above can be used. However, here is a software that can directly convert RM for MP3 format: streambox ripper, I am using V 2.009 version. It is also very simple. When you start, click the "LOAD" button, select the RM file you want to convert, return to the main interface, click the "Convert" button, select "MPEG LAYER 3" in "Encode Output File" (Input File Format) (MP3) ", modify the location you want to save in the save directory, then click" OK ", you can start to convert. In addition to the file format mentioned above, there are not many formats used on the MP3 machine. The most simple method: The most famous music play software WINAMP, as long as it supports playing your file format (can play most formats through the plugin), you can convert to WAV format, on this basis, you can convert It is MP3 or WMA.
