What is Lossless Compression?

The so-called lossless compression format is to use the statistical redundancy of the data for compression, which can completely restore the original data without causing any distortion, but the compression rate is subject to the theoretical limit of the statistical redundancy of the data, which is generally 2: 1 to 5: 1. This type of method is widely used for compression of text data, programs, and image data (such as fingerprint images, medical images, etc.) in special applications.

The so-called lossless compression format is to use the statistical redundancy of the data for compression, which can completely restore the original data without causing any distortion, but the compression rate is subject to the theoretical limit of the statistical redundancy of the data, which is generally 2: 1 to 5: 1. This type of method is widely used for compression of text data, programs, and image data (such as fingerprint images, medical images, etc.) in special applications.
Chinese name
lossless compression
Basic explanation
Compression with data redundancy without distortion
Compression method
Shannon-Fano encoding, etc.
Advantages
No signal loss; high sound quality
Deficiencies
Large footprint; lack of hardware support
Lossless format
PE, FLAC, TAK, WavPack, etc.

Lossless compression overview

Due to the limitation of compression ratio, it is impossible to solve all the problems of image and digital video storage and transmission using only lossless compression methods. The commonly used lossless compression methods are Shannon-Fano encoding, Huffman encoding, and run-length encoding.
LZW (Lempel-Ziv-Welch) coding and arithmetic coding.
The so-called lossless compression format, as its name implies, is an audio format that compresses sound signals without loss. Common formats such as MP3 and WMA are lossy compression formats. Compared with the WAV file as the source, they all have a considerable degree of signal loss, which is the root cause of their 10% compression rate. The lossless compression format is like compressing audio signals with compression software such as Zip or RAR. The resulting compression format is restored to a WAV file, which is exactly the same as the WAV file as the source! However, if you use Zip or RAR to compress WAV files, you must decompress the compressed package before playing it. The lossless compression format can be real-time playback directly through the playback software, which is exactly the same as lossy formats such as MP3. All in all, a lossless compression format is a format that can reduce the volume of a WAV file without sacrificing any audio signal.

Advantages and disadvantages of lossless compression

Lossless compression advantages

1.100% preservation without any signal loss
As mentioned before, the lossless compression format is just like Zip compressed files, which can save all the data of the WAV file 100%. This can be proved by the "WAV comparison" function of EAC. Save a beautiful day by U2
lossless compression
Into WAV format as our original file. Compress the WAV file into APE format, and then decompress the APE file into WAV format. Use the "WAV Compare" function of EAC to compare the data of these two WAV files. The result is shown in Figure 1. EAC did not report any inconsistency! If it is a WAV file compressed into MP3 and then decompressed, compared with the original WAV file, it is inconsistent from beginning to end! Many friends hope that they can copy the "original" CD to the hard disk to the greatest extent, and at the same time want to reduce the amount of space occupied. This seems to be only a 320Kbps CBRMP3 solution before, but that is far from 100% !! The advent of lossless compression formats provides an almost perfect solution.
2, high sound quality, not affected by the signal source
Since the original audio signal is 100% saved, the sound quality of the lossless compression format is undoubtedly the same as that of the original CD! Compared with the spectrum diagrams of "BeautifulDay" in the WAV format and the FLAC compression format, can you see any differences? Similarly, there can be no difference in actual listening! The lossy compression format is due to its inherent design (a part of the signal needs to be lost), so no matter how good the sound quality is, it can only be infinitely close to the original CD. And due to the limitations of the lossy compression format algorithm, when compressing music with a large dynamic range, such as symphony, the sound quality performance is unsatisfactory. The lossless compression format does not have such a problem, and any type of music is correct!
3.Convenient conversion
Lossless compression format can be easily restored to WAV, can also be directly converted to MP3, Ogg and other lossy compression formats, and can even convert between different lossless compression formats without losing any data. This is much stronger than the lossy format! Because the secondary encoding of the lossy compression format (converting from one lossy format to another, or adjusting the bit rate without changing the format) means that more signals are lost, resulting in greater distortion!

Insufficient lossless compression

1. Large space occupation and low compression ratio
Compared with the lossy compression format, the lossless compression format has a much lower compression capacity, generally around 60%. The lossy format of 192Kbps is only about 14% of the original file, and the difference in compression ratio between the two is quite different. As shown in Figure 5, a U2 "BeautifulDay" is compressed in different formats, including APE in Normal mode and La in High mode. However, it can be seen that the data is also 100% saved. The lossless format has a stronger compression capability than RAR, which is optimized for multimedia formats. Zip can hardly compress the WAV format. In addition, the lossless format has real-time playback capabilities that neither RAR nor Zip has, and we still quite admire the technology of lossless format!
2.Lack of hardware support
The FLAC format is only supported by a few hardware [1] , but Sony's atrac advanced lossless has extensive support in Sony Walkman. Walkman that can play lossless compression format In addition to Karma, there are Sony nw-x1000 series, nw-a840 series, nw-s740 series. The capacity of mainstream flash MP3 players has been 4GB to 16GB. But few people know about lossless formats, and few people are willing to spend time downloading music. The market demand is small and the supply is naturally small. Therefore, the development of the Walkman is slow and support for lossless is less.

Lossless compression lossless format

The more famous lossless compression formats are APE, FLAC [2] , TAK, WavPack, TTA, etc.

AAL Lossless compression AAL

ATRAC Advanced Lossless is an ATRAC format developed by Sony CorporATIon. By combining the audio compression technology behind ATRAC3 or ATRAC3plus and the latest lossless compression algorithm, the lossless compression of data is perfectly realized with a very low data size while maintaining compatibility with traditional devices. Referred to as AAL file, some HI-MD products have been upgraded to support AAL files.
The AAL file is divided into two parts, one is 256k A3plus can also be other A3 or A3 +, and the other is detailed music information. So for ordinary Sony Walkman, there is only 256K part of playback. Only machines that really support AAL can play other details.

APE Lossless compression APE

APE (Monkey's Audio) is undoubtedly a well-known lossless compression format, which has been widely used in China. Its compression ratio is very good, and it has high efficiency and fast speed, and its comprehensive ability definitely belongs to today's best. Through BT or eDonkey you can download a lot of music in APE format. And the widely used Monkey'sAudio production software has greatly promoted the popularity of the format. However, APE also has many shortcomings. Its decoding speed is not ideal. It requires high CPU computing power and can only be used on the Windows platform. Any data corruption will cause the entire file to be scrapped. In addition, although APE provides the source code for free, it is not an open source agreement, which leads to restrictions on improvement. Therefore, the APE format is going downhill, and some European and American music forums have abandoned the format.

FLAC Lossless compression FLAC

FlAC (FreeLosslessAudioCodec) is a very mature lossless compression format. The format's source code is completely open and compatible with almost all operating system platforms. Its encoding algorithm is quite mature, has passed rigorous tests, and it is said that it can still play normally when the file point is damaged (the damaged part is replaced by mute). This format has not only mature Windows authoring programs, but also support from many third-party software. In addition, this format is the only lossless format that has been supported by the hardware. Rio s hard disk player Karma, Kenwood s car audio MusicKeg, and PhatBox s digital players all support FLAC format.

WavPack Lossless compression WavPack

Quite characteristic format, well worth a try. WavPack is more than just a lossless compression
Lossless compressed file
It also serves as a lossy compression format. In its unique "hybrid" mode, WavPack can be compressed into wv files (lossy compression format, generally equivalent to about 23% of WAV files) + wvc files (corrected files, generally equivalent to about 41% of WAV files )The combination. With the corresponding wvc file, the wv file in the lossy compression format becomes a lossless format, which is exactly the same as the ordinary lossless compression format during playback. If you want to reduce the file size, you can remove this wvc file, then the wv file will become a lossy format, and it will play exactly the same as a high bitrate MP3! WavPack includes both lossless and lossy formats. Amazing? With the WavPackFrontend front-end program, we can easily use the WavPack format.

LPAC Lossless compression LPAC

In the non-destructive format of the medium orbit moment, all indicators are relatively average. Author Tilman Liebchen has prepared a good production program for it, but has stopped updating independently, but as a standard for MPEG4.

WMALossless WMALossless

Microsoft has also started providing lossless compression in Windows Media Player 9.0. Just click the menu "Tools" = "" Options "and select the" WindowsMedia Audio Lossless "format in the" Copy Music "tab. In the future, through WMP's "Copy from CD" function, you can directly save the CD into WMALossless format, which is really very convenient to use. Except for WindowsMediaPlayer, almost no other software can support this format.

AppleLossless Lossless compression AppleLossless

The latest version of Apple iTunes music software also provides AppleLossless lossless compression format. Like WindowsMediaPlayer, iTunes can quickly grab and compress tracks from CDs into AppleLossless format. Of course, this format is also only supported by its own software.

La Lossless compression La

La is the abbreviation of LosslessAudio. Although the format is not well known, it is the champion of compression ratio. No one can match the compression ratio, including APE, which has always been known for its high compression ratio! Just because the compression is too strong, its encoding and decoding speed is really slow, and there are relatively few software to support it. Only limited to the Winamp decoding plug-in developed by himself and LosslessAudioCompressor, the encoder of the Windows interface.

OptimFROG Lossless compression OptimFROG

The compression rate of this format is comparable to La, but it is slower than La.

Shorten Lossless compression

Very fast lossless encoding, but the compression rate is disappointing! This format is also open source and supports both Windows and Mac, but it has not been updated for a long time. It is estimated that it has died.
Lossless compression formats are far more than just the above. There are also RKAU, SZIP, Bonk, Kexis, etc., because they are very rare and imperfect, they will not be introduced.

Kenwood Lossless compression Kenwood

Kenwood's original lossless compression method (Kenwood Lossless) to record the content of high-quality music CDs, which can more effectively use the capacity of the hard disk memory to store more data (average compression rate of 60%), but also can effectively compress The files are restored to their original state so that high-quality sound quality can be guaranteed.

TAK Lossless compression TAK

TAK (Tom's Audio Kompressor) is a new lossless audio compression format. The full name is Tom's Audio Kompressor. It is produced in Germany and its popularity is increasing. Not open source, but the author says that it will be open source in due course. The latest version is 2.0, and TAKs with higher version compression cannot be recognized by lower versions. It is similar to FLAC and APE. In general, the compression rate is similar to APE and the decompression speed is similar to FLAC, which is a combination of the advantages of the two. In addition, the audio compressed by the encoder in this format is VBR, which can change the bit rate.
Several major features:
-Excellent compression ratio. The compression ratio using the Extra parameter is similar to the High parameter of the APE, and the results obtained using the fastest compression parameter TAK Turbo and the parameter effect with the largest FLAC compression ratio are comparable.
-Faster compression speed. The author says that at the same compression rate, he understands that there is no other format that can compress the parameters of Turbo and Fast of TAK faster.
-Very fast decompression speed. Similar to FLAC's decompression speed.
-Support conversion of many common audio formats to TAK.
-Stream support. Every two seconds, a burst containing all the information needed for decoding is inserted into the audio.
-Fault tolerance. One bit of information is wrong, affecting up to 250 milliseconds of audio. Due to the above-mentioned technical support, severely damaged audio compressed using this format can also be played back, at the cost of the damaged part being replaced by mute.
-Error checking. A 24-bit CRC check is used on each frame.
-Simple and fast search capabilities. That is, when you need to play from a certain point in the middle, you can quickly find the place you want to start playing, and the positioning is very accurate.
-Support audio information. At the same time support the use of external CUE to split the audio track and add audio information. Similar to APE.

TTA Lossless compression TTA

TTA (True Audio) is a free and simple real-time lossless audio codec, but its popularity is declining. TTA is a lossless audio compression based on adaptive prediction filtering. Compared with other major formats, it can have the same or better compression level, while maintaining a higher speed.
The characteristics of TTA lossless audio coding are:
First, the compression ratio can reach 10: 3; second, real-time encoding; third, free and open source code and files; fourth, compiling on different platforms; fifth, simple and convenient data format; sixth , Can be used as an input plug-in for various music players; seventh, to provide a graphical user interface (GUI) for Windows users; eighth, DirectShow technical support.
The TTA lossless audio codec can compress multi-channel audio files in 8-, 16-, and 24-bit data formats. The result of this compression is no data or quality loss; when decompressed, it is the same as the data bits of the source audio file. The different compression ratios achieved by the TTA decoder depend on the type of music, but range from 30%-70%. The TTA lossless compressed audio format supports ID3v1 and ID3v2 tag information.
The TTA lossless audio codec can store up to 20 audio CDs of music, which is equivalent to a single DVD-R, and retains the original CD sound quality and details of the popular ID3 tag format.
All TTA source and binary code is provided free of charge and distributed under an open source license.

Lossless compression prospects

Although there are still some shortcomings, the prospect of lossless compression formats is undoubtedly bright. This can be seen from the many types of lossless compression formats that exist! Over time, the factors limiting the lossless format will be gradually eliminated! For example, the capacity of hard disks continues to increase, 1TB of mechanical hard disks has become mainstream, and 200GB of solid-state hard disks will also become popular. The problem of large space occupied by non-destructive formats will no longer be a problem. A faster decoding chip will also be developed. It is believed that more and more hard disk players will support lossless formats. In the near future, when even the capacity of the flash player is calculated in TB, in order to pursue higher sound quality, the lossless compression format will be more and more valued!

TAC Lossless compression TAC

As the leading music service platform in China, it has developed and launched a lossless format TAC music exclusively for the majority of users. Unlike lossy compression methods such as MP3, tac is a lossless audio compression technology that Tencent encrypts and produces on the basis of FLAC. The essence is The modified FLAC format, like other lossless formats, guarantees no loss of sound quality. Due to the closed encryption method, the format can ensure that the achievements of the copyright owner of the music are not pirated and infringed, and that the music can only be played on the QQ player and not copied to any unauthorized player for playback. Green Diamond users only need to select the high quality to download in the music library, select "lossless sound quality" in the "select sound quality" section of the download page, and click "start download", and the user can easily collect unlimited good music.

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