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Structure of an mp3

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Structure of an mp3

audio compression

The MP3 format began in the mid-1980s and the Fraunhofer Institute in Erlangen, Germany, was committed to high-quality, low-data-rate audio coding.

MP3 audio compression includes encoding and decoding in two parts. Encoding is converting the data in the WAV file into a highly compressed bitstream format, and decoding is accepting the bitstream and reconstructing it into the WAV file.

MP3 uses the distortion algorithm of Perceptual Audio Coding (PerceptualAudioCoding). The frequency range of sound perceived by the human ear is from 20 Hz to 220 kHz. MP3 cuts out a lot of redundant signals and irrelevant signals. The encoder transforms the original sound into the frequency domain through a hybrid filter bank. Using the psychoacoustic model, it is estimated that it may simply be The perceived noise level is quantized and converted to Huffman coding to form an MP3 bitstream. The decoder is much simpler and its task is to extract the sound signal from the encoded spectral line components through inverse quantization and inverse transformation.

When compressing audio data, the original sound data is first divided into fixed blocks, and then direct MDCT is performed. MDCT itself does not perform data compression, but only converts a set of time-domain data to frequency-domain data to obtain time-domain data. In case of change, the direct MDCT converts the value of each block into 512 MDCT coefficients. Quantization compresses data, and when bits are allocated to transformed samples after quantization, it is necessary to consider making the entire quantized block the smallest, which becomes lossy compression. When decompressing, the 512 coefficients are restored to the original sound data by reverse MDCT, and the original sound data before and after are inconsistent, because redundant and irrelevant data are removed during the compression process.

MP3 file structure
MP3 files are roughly divided into three parts: TAG_V2(ID3V2), Frame, TAG_V1(ID3V1)

ID3V2 Contains information such as author, composer, album, etc., the duration is not fixed, expanding the amount of information of ID3V1
framework

A series of frames, the number is determined by the file size and frame length

The length of each frame can be variable or fixed, determined by the bit rate.

Each FRAME is divided into two parts: frame header and data entity

The frame header records the bitrate, sample rate, version, and other mp3 information, and each frame is independent of each other.

ID3V1　　　 Contains author, composer, album and other information, length is 128BYTE

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Structure of an mp3

The full name of MP3 is MPEG Audio Layer3, which is an efficient computer audio coding scheme.

Structure of an mp3

It converts audio files into smaller files with .MP3 extension with a higher compression ratio and basically keeps the sound quality of the original file. MP3 is part of the ISO/MPEG standard. The ISO/MPEG standard describes audio compression using a high-performance perceptual coding scheme. This standard has been continuously updated to meet the pursuit of “high quality, low volume”. MPEGLayer1, Layer2 , and Layer 3 have now formed three audio codec schemes. The compression rate of MPEGLayer3 can reach from 1:10 to 1:12. A 1M MP3 file can play for 1 minute, while a 1 minute CD-quality WAV file (44100 Hz, 16-bit, two channels, 60 seconds) will take up 10M of space. , A 650M MP3 disc should play for more than 10 hours, while a CD with the same capacity should play for about 70 minutes. The advantages of MP3 are unmatched by CD.

MPEG audio standard
MPEG (Motion Picture Experts Group) is a moving picture expert group under ISO, and the MPEG standard it creates is widely used in various multimedia. MPEG standards include video and audio standards, among which MPEG-1, MPEG-2, MPEG-2AAC, and MPEG-4 audio standards have been developed.

The MPEG-1 and MPEG-2 standards use the same family of audio codecs: Layer 1, 2, and 3. A new feature of MPEG-2 is the use of low sample rate expansion to reduce data traffic, and another feature is multi-channel expansion, which increases the number of main channels to five. The MPEG-2AAC (MPEG-2 Advanced Audio Coding) standard was released by FraunhoferIIS and AT&T in 1997, with the goal of significantly reducing data traffic. MPEG22AAC adopts the Modified Discrete Cosine Transform (MDCT) algorithm and the sampling rate can be between 8 KHz and 96 KHz. The number of channels can be between 1 and 48.

MPEG Audio Layer1, 2, and 3 use the same filter bank, bitstream structure, and header information, and the sample rate is either 32 KHz, 4411 KHz, or 48 KHz. Layer1 is designed for DCC (DigitalCompactCassette) digital compression tape, the data rate is 384kbps, Layer2 has made a compromise between complexity and performance, and the data rate has been reduced to 256kbps-192kbps. Layer 3 was designed for low data traffic from the start, and data traffic ranges from 128 kbps to 112 kbps. Layer 3 adds MDCT transform, making its frequency resolution 18 times higher than Layer 2. Layer 3 also uses EntropyCoding similar to MPEGVid2eo, reducing redundant information. The vast majority of MP3s use the MPEG21 standard.

What are MP3 files?

The audio format is directly related to the quality and purpose of the audio track, i.e. where and on which device it will be played and what is its purpose.

What are MP3 files?

But before you can figure out the difference between them and choose the best audio format for your music, you need to know what categories they fall into. Let’s keep going!

Uncompressed audio is like a picture, and uncompressed audio is of better quality, larger file size, safer to copy, and nearly identical in detail to the original sound.

WAV is the most widely used of these audio formats and plays music just as accurately as it records it.

compressed audio
When music is compressed, the files become smaller and can be easily stored on a device. Due to this advantage, users tend to choose compressed audio more.

However, it must be remembered that some audio formats in this category may lose quality depending on the option selected, just like MP3 and AAC.

What is the best audio format?
As we said before, the first step in deciding on an audio format is to know the final objective of the track. Whether it’s for music lessons, performances, karaoke, auditions, or recording versions, you need to understand the pros and cons of each option.

WAV
WAV (Waveform Audio File Format) is an uncompressed format and therefore requires ample storage space. This is suitable for those who already work with music, such as subject matter experts, or users who want to edit audio.

At high fidelity rates, WAV faithfully reproduces the elements and characteristics of the original soundtrack. Also, this format allows you to choose between different sample rates and bit rates and can be used on multiple platforms.

FLAC
FLAC (Free Lossless Audio Codec) is one of the most widely used compression formats by music lovers these days.

Digital audio encoding allows you to preserve its quality, but the resulting file will be smaller. Over the years, this format has become more widely used and compatible with different devices and platforms.

FLAC is free and open source, ready to use and can be easily played on smartphones and other devices.

MP3
Before deciding on the best audio format, it is worth taking a look at the most famous format in the world of music: MP3.

MP3 is one of the leading audio compression formats, and has become synonymous with the convenience and efficiency of producing files quickly, with smaller files, and at a certain level of quality.

Many devices and programs can play this format. But MP3 is difficult to use in professional audio processing and advanced audio editing.

As is known, this format exists on almost all platforms and is ideal for sharing audio.

Another interesting factor is its bitrate, although in a compressed format it can vary depending on the user’s objectives and quality improvements.

AAC Like MP3, Advanced Audio Coding (AAC) is a more efficient audio format than its predecessor.

If you need to create smaller files with less storage space, AAC is a great choice, reducing the file size for the user while maintaining a high-quality audio track.

Compatible with different platforms and devices, it is convenient to apply in different situations.

Analysis of the above audio formats leads to the conclusion that it is impossible to say which format is better than the other, just that each target has its own ideal format. So before downloading or uploading a file, check what platform the music will play on and what it is for.

What are MP3 files?

A file with the .mp3 extension is a digitally encoded file format for audio files, officially based on MPEG-1 Audio Layer III or MPEG-2 Audio Layer III.

It was developed by the Moving Picture Experts Group (MPEG) using Layer 3 audio compression. The compression achieved by the MP3 file format is 1/10 the size of a .WAV or .AIF file. This format offers the advantage of streaming such audio files over the Internet for online listening, which was previously not possible due to the large size of audio files. The sound quality of MP3 audio files can be controlled by setting parameters such as bit rate, sample rate, common or normal stereo.

A brief history of MP3

The MP3 format was invented and developed by a German company, Fraunhofer-Gesellshart. The algorithm has licensed patents for the compression techniques it uses. Here’s a helpful MP3 schedule:

• 1987 : The Fraunhofer Institute in Germany begins research on high-quality, low-bitrate audio coding. It’s called the EUREKA project EU147, Digital Audio Broadcasting.

• January 1988: The Moving Picture Experts Group (MPEG) is formed.

• **April 1989**: Fraunhofer patented the MP3 in Germany.

• 1992-Dieter Seitzer, who helped Fraunhofer with his research, integrated his audio encoding with MPEG-1.

• 1993 – Publication of the MPEG-1 standard.

• 1994 – The MPEG-2 standard was developed and released a year later.

• November 26, 1996 : US patent for MP3 is published.

• September 1998 – Fraunhofer begins to enforce the patent. People who used the MP3 audio codec paid Fraunhofer a license fee.

• February 1999 – SubPop, a record label, releases music in MP3 format, the first to do so.

• 1999 – The first portable MP3 player appears.

File format MP3##
MP3 files consist of MP3 frames, where each frame consists of a header and a data block. Frames are not independent and generally cannot be mined at arbitrary frame boundaries. The data blocks of a file contain frequency and amplitude information about the audio. The sync word in the header identifies the start of a valid frame. This is followed by 3 bits where the first bit indicates that it is an MPEG standard and the remaining 2 bits indicate that layer 3 is used; therefore, MPEG-1 Audio Layer 3 or MP3. After this, the value will vary depending on the MP3 file. ISO/IEC 11172-3 defines the range of values for each part of the header and the header specification. Most current MP3 files contain ID3 metadata, which precedes or follows the MP3 frame, as shown. Data streams may contain an optional checksum.

Mp3 is still the best audio format

Does this phrase remind you of the fear of being dominated by “storage space” in those years?

This also shows from the side that in the years when storage technology was underdeveloped, MP3, which could compress the file size, was like a “black technology” for users at that time.

But after MP3 became popular, controversy also followed. Since MP3 allows anyone to rip CDs, make, copy and distribute music files to anyone, to a certain extent, it can be said that MP3’s dominance of the “global music format” is based on rampant pirated music. . However, from another perspective, these problems that MP3 brings with it are also forcing the music industry to start thinking about legalizing digital music.

What is the origin of the AAC?

AAC (Advanced Audio Coding) and MP3 are lossy compressed audio data formats. In 1997, it was jointly developed by Fraunhofer IIS, Dolby Laboratories, AT&T, Sony, and other companies to replace the MP3 format.

AAC is much younger than MP3, and the technology it was born into has far surpassed MP3. According to public information, AAC uses a new algorithm for encoding, which is more efficient and has a higher “cost performance”. As Fraunhofer IIS says, AAC looks better than MP3 in every way.

Although AAC is better than MP3, but MP3’s market share is too high. It is almost impossible for AAC to change the “MP3 inertia” of the user.

Fortunately, not everyone refuses to support AAC. Apple is one of the supporters of AAC. It started to provide AAC format for users to download as soon as possible. Li Chujie, founder of MOZIK music player, said:

In 2006, I bought my first iPod from Apple and it supported AAC files. All MP3 formats that I download from the Internet are converted to AAC files. It was also through this that I noticed the difference in sound quality and byte size between MP3 and AAC.

In the early days, apart from Apple, there were devices like Sony Walkman (NWZ-A, NWZ-S, NWZ-E, NWZ-X series), Nintendo NDSi, and Meizu that supported AAC. Later, as more and more music lovers paid attention to AAC, users gradually recognized its advantages. Both the number and category of hardware devices that support AAC have grown rapidly.

Mp3 is still the best audio format

Mp3 Audio

MP3, the king of music formats, has retired from the stage of history and been replaced by AAC. What is the origin?

Even someone who knows nothing about audio encoding may not have listened to MP3.

This audio format emerged in the 1990s. For most post-80s and post-90s generations, having an MP3 player capable of playing this audio format is one of the best childhood memories.

But now it’s time to say goodbye to MP3s. Recently Fraunhofer IIS, which invented this audio format, announced that it had rescinded some patents related to MP3 and officially took it off the stage of history.

Furthermore, Matthias Rose, director of the institute, said:

The Advanced Audio Coding (AAC) format has become the standard for mobile music and video downloads. This format is more efficient, more functional, and has a lower bit rate than MP3, and is used in both broadcast TV and radio to deliver high-quality audio.

This means that Fraunhofer IIS wants to replace MP3 with the AAC format below.

How did MP3 become the king of music formats?
There are generally two main types of audio file formats, one is a lossless compressed data format and the other is a lossy compressed data format.

MP3 is the most popular digital audio encoding and lossy compression format, and is supported by almost all terminals and software.

The birth of MP3, but also for 30 years. In 1987, Fraunhofer IIS in Germany began the development of the music compression format. They spent 4 years to improve the algorithm and sound quality, and finally developed this very advanced lossy compression audio format in 1993 and determined the extension .mp3.

The purpose of developing this audio compression technology is to greatly reduce the amount of audio data. Knowing that hard drives at the time were relatively small (like 500 MB), compressing all compressible data was essential for any computer user.

How does Fraunhofer IIS do it? During the invention of MP3, developers studied psychoacoustics and determined that some of the audio data is not important to the human ear. MP3 achieves the purpose of compressing the file size by discarding this part of the data, and can successfully compress the audio file to 1/10 of the original size.

After that, from the first half of 1995 to the end of the 1990s, MP3 began to flourish on the Internet. The “much smaller file but also good sounding” MP3 began its era of dominating audio formats. There were even many people at the time who believed that all digital music files were MP3s.

Does it make sense to use lossy compression at all?

Does it make sense to use lossy compression at all?

MP3

Let’s try to outline the limits of mp3 usage. As long as the sound quality does not have to be exactly the same as the original, and where serious processing of stored data is probably not required in the future, the use of mp3 (or other lossy compression format) is perfectly acceptable. . Not everyone wants to insert a new music disc into a CD drive every hour if the hard drive’s capacity is tens of gigabytes. It is much easier to burn mp3 music to a hard drive or CD-ROM and listen from there. Or use a portable mp3 player, MP3-CD player, car radio with mp3 support. Or you can just download mp3 from the internet to choose from.

mp3

In this subsection and subsequent ones, we will describe cases where the use of lossy compression is unacceptable and also try to find out why.

There is no point in creating audio data files for further processing (sample libraries, music libraries, etc.) in mp3. This also applies to MiniDisk (which also uses lossy compression) and other formats – many types of digital processing involve audible distortion. This rule is independent of the bit rate used. Speaking of more sound processing, I mean something more serious than just mixing or fade in / out, for example flange, distortion, dynamic compression, reverb, noise filtering and even the use of an equalizer … For example , you cannot store samples in mp3 (to store them use special lossless compression formats, for example sfArk). Since in the case of lossy encoding it is impossible to recover the data lost at the encoding stage, then in mp3, it is convenient to save only the final versions of sound recordings.

One more argument: do you know how to re-burn an audio disc converted to mp3 to an audio CD so there are no additional pauses or clicks between tracks? I do not know? Visit, say, www.r3mix.net. It’s still a hassle … If you want to say, “But I did it, everything is fine!” – Let’s get the job done: the music should move seamlessly from track to track, and a pause is considered not only an interval of 1-2 seconds, but also small segments of silence in units of tens of milliseconds. In theory, in this case, everything can be done perfectly together, but it may turn out that “the game is not worth it.”

What are the ways to store lossless audio?
I save my music library in wav files (in PCM format). You can also use CD-DA; It is characterized by better compatibility, but lower reading precision during playback. There are other options: regular archiving (ZIP, RAR) or special programs like WavPack, Monkey’s Audio, RK Audio, FLAC, LPAC Archiver, Shorten … However, working with archives compressed in this way is fraught with unpleasant surprises: wav ( PCM) is played by the vast majority of players, but exotic things like RKA … It is known about the existence of a plug-in for RKA under WinAmp, but WinAmp was not found as a wedge: there are people who are not used. Therefore, WinAmp alone is not yet supported (in a broad sense). What about other player programs? What about hardware players? What about MP3-CD players? I don’t know about you, but for me compatibility in the above sense is very important. And using just one encoder / player pair limits your freedom significantly. For example, in order for your friends to be able to listen to a file, you must convince them of the need to use a new player.

What considerations should be taken into account when choosing compression options?
In my opinion, two main compression modes can be distinguished: “maintaining an acceptable level of quality when reaching maximum compression” (for example, for publishing on the Web) and “completely subjective preserving the quality of the source material without the greatest compression “(for regular storing and listening) … It is worth noting that the threshold bit rates for both modes are individual. For me, it’s 128 and 256 kb / s, respectively. Of course, there are many options in between: there is a portable mp3 player with bottom headphones, which is sufficient for 160 kb / s; the car has a radio recorder with mp3 support and better acoustics; here you need, say, 192 kb / s. Therefore, when choosing compression parameters, you must first determine the tasks for which mp3 files are created, and based on this, work out what ratio of sound quality to file size suits you. It should also be noted that the concept of sound quality can vary greatly from person to person.