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MP3 File Structure Analysis Part 2

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MP3 File Structure Analysis Part 2

Sounds in nature are very complex and waveforms are extremely complex.

Usually we use pulse code modulation coding, that is, PCM coding. PCM converts continuously changing analog signals into digital codes through three steps of sampling, quantizing, and encoding.

u Decode:

Reverse encoding process

1.1.2 Brief introduction of MP3
The full name of MP3 is MPEG Audio Layer 3. It is an efficient computer audio coding scheme. It converts audio files into smaller files with a .mp3 extension with a higher compression ratio, essentially maintaining the sound quality of the source 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 and low quality”. Three audio codec schemes, MPEG Layer1, Layer2 and Layer3, have been formed, respectively, corresponding to the three sound files MP1, MP2 and MP3

MPEG (Moving Picture Experts Group) is a group of moving picture experts under ISO. The MPEG standard it specifies is widely used in various multimedia. The MPEG standard includes video and audio standards. Audio standards have developed MPEG-1, MPEG -2, MPEG-2 ACC, MPEG-4. The MPEG-1 and MPEG-2 standards use the same family of Layer1, 2, 3 audio codecs, and most MP3s use the MPEG1 standard.

MP3 audio compression consists of two parts: encoding and decoding. Encoding is the process of converting the original signal to a level signal, and decoding is the reverse process. MP3 uses the PerceptualAudio Coding distortion algorithm. The frequency range of sound perceived by the human ear is 20 Hz to 20 kHz. MP3 cuts out a lot of redundant signals and irrelevant signals. The encoder transforms the original sound into the frequency domain through a mixed filter bank and uses a psychoacoustic model. to estimate that it may be only The perceived noise level is quantized and converted to Huffman coding to form an MP3 bit stream. The decoder is much simpler, its task is to extract the sound signal from the encoded spectral line components through inverse quantization and inverse transformation.

MP3 file data consists of multiple frames, and a frame is the smallest unit of an MP3 file. Each frame, in turn, consists of a frame header, additional information, and sound data. The playback time of each frame is 0.026 seconds and its duration varies with the bit rate. Some MP3 files have extra bytes at the end that contain description information for non-audio data.

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MP3 file structure analysis

ü ID3:

Usually located in several bytes at the beginning or end of an mp3 file, it records the singer, title, album name, era, style, and other mp3 file information.

ID3 is divided into two versions, the V1 ID3 version is fixed at the end of the 128-word file section, it begins with the TAG character, if there is no ID3V1 information, it is considered that there is no ID3V1 information, the V2 ID3 version is found. at the beginning of mp3 and the length is variable.

ü Sampling rate:

The number of samples extracted from a continuous signal to form a discrete signal per second. It is expressed in Hertz (Hz). Sampling rate refers to the sampling frequency when converting an analog signal to a digital signal, i.e. how many points are sampled per unit of time. The higher the sample rate, the more realistic and natural the sound will be. On today’s major capture cards, the sample rate is generally divided into three levels: 22.05 KHz, 44.1 KHz, and 48 KHz. 22.05 KHz can only achieve the sound quality of FM radio, and 44.1 KHz is the theoretical limit of CD sound quality, and 48 KHz is more accurate.

ü Bit rate:

Bit rate refers to the number of bits (bits) transmitted per second. The unit is bps (bit per second). The higher the bit rate, the more information transmitted. In the audio and video fields, bit rate often translates to bit rate. The bit rate indicates how many bits per second the encoded (compressed) audio and video data should represent, and a bit is the smallest unit in binary. 0 or 1. The relationship between bitrate and audio and video compression is simply that the higher the bitrate, the better the quality of the audio and video, but the larger the encoded file; if the bitrate is lower, the situation is just the opposite.

Bit rate = sample rate * number of samples * number of channels

ü Bitrate/Stream/Bitrate:

It refers to the data stream used by audio and video files in a unit of time. The popular understanding is the sample rate, which is the most important part of quality control in audio and video encoding. Generally, the units we use are Kb/s and Mb/s. . Generally speaking, the higher the code stream, the lower the compression ratio and the higher the quality. The higher the code stream, the higher the sampling rate per unit time, the higher the data stream, the higher the accuracy, and the closer the processed file is to the original file.

ü Code:

From the point of view of information theory, the data that describes the source of information is the sum of the redundancy of information and data, namely: data = information + data redundancy. The audio signal has correlation in the time domain and the frequency domain, that is, there is data redundancy. Taking audio as the source, the essence of audio encoding is to reduce redundancy in the audio.

Advantages and disadvantages of MP3 technology.

In the internet age, MP3 has become a de facto standard for digital audio files. Napster’s popular peer-to-peer application allowed music lovers to exchange MP3 files so they could get songs without paying for it. This article is written to guarantee the pros and cons of MP3, to help you decide whether to convert your existing music files to MP3 in a different format or not.

mp3 advantages

Advantages of MP3

The advantage of MP3 is the high quality. The quality of an MP3 file is determined by the bit rate. Flow is measured in kilobits per second. The bit rate of an MP3 file can range from 8 kbps to 320 kbps. You should keep your songs at 160 kbps if you don’t really like them and don’t put them at the top of your list of mp3 players. Keep your songs at 192 kbps if you like them a bit. Use 256 kbps for the songs you like. And use 320 kbps for your all-time favorite songs. Regardless, even an 320kbps MP3 doesn’t sound as good as the song’s WAV file version. But a 320kbps MP3 takes up four times less space than a WAV file. To use an analogy, an MP3 file is a WAV file, which is a JPEG image of a BMP image.

Problems

The second advantage is that it can be played on many types of devices, such as CD players and Apple iPods. You can also play MP3 files with multimedia players such as Winamp, Windows Media Player or QuickTime. The third advantage of MP3 is ID3 tags. The ID3 tag of an MP3 file stores the artist name, song title, year, and genre. You can also create your own playlists.

Another advantage of MP3 is that encoding is simple. It is easy to rip audio CDs and burn as easily as regular MP3 CD-Rs. The encoding speed is also very fast, but it also depends on the speed of the CD player. Producing MP3 files takes very little time. You can use lossless audio compression if you have a lot of free disk space and lossy audio compression if you have little free disk space. The MP3 LAME encoders are free and open source, so that everyone can contribute to their development.

Another plus of MP3 is that the layout is simple. MP3 can be downloaded from HTTP or FTP sites. You can also distribute MP3 files through portable storage devices such as USB flash drives. You can also buy MP3s from online music stores such as iTunes and eMusic.

You can also use a server to distribute these files. Listening to it in MP3 uses an M3U playlist format such as (which means MP3 URL) or PLS. MP3 streaming is also used by internet radio stations. You can integrate MP3 streams with a Flash player. You may have different rates for dial-up and broadband connections. MP3 audio is not stored on your hard drive.

MP3 problems

A disadvantage of MP3 is that it takes up a lot of storage space. Since an MP3 file generally takes up to 5 megabytes (MB) of disk space, the number of files it can store is limited. Due to the relatively large size of an MP3 file, the slow file can also be downloaded if you have a slow internet connection.

Another problem is that the song can jump to random places. This happens especially if you have a slow computer and use multiple programs that load the processor at the same time. It is technically not free. You also need an MP3 decoder if you want to convert MP3 audio files to WAV format. The MP3 format has very little security available. For example, people who used the Morpheus file sharing service had their computers accessible to hackers.

Another limitation is that this file is not the best fidelity format for audio files. Other audio formats, such as Ogg Vorbis and Advanced Audio Coding (AAC), are superior in quality to MP3. AAC is the format used in the Apple iTunes player. However, MP3 is still the most popular audio format in the world.

The pros and cons of MP3, which I just mentioned will help you make a good decision before downloading music next time.

MP3: analysis of an MP3

Different formats are used on the internet to let you listen to music. We will choose the MP3 format here.

On this page you will find all the help you need to listen to music on the internet and understand how it works. We answer the questions: What is MP3? Do radios use MP3? Why the MP3? Are record companies afraid of MP3? Mp3 is legal? How to listen and find an MP3? What is the future of MP3? Is the future of free MP3 in danger?

mp3 format

What is MP3?

MP3 (Mpeg-1 Audio Layer 3) is a destructive or compressed file format for data loss. A song deletes all data that may not be heard by the human ear. It is defined by ISO / IEC standards IS 11172-3 and IS 13818-3 and is recommended by the MPEG (Moving Pictures Experts Group).

mp3

The advantage of this format is that it can achieve a high compression rate in the sound file (for example, wav extension) without affecting the sound quality. The difference between the original sound of a compact disc and the compressed one in MP3 is inaudible. The compression speed is 1/12 (or even more than once, but in this case the quality is palpable), the files thus obtained have a really reasonable size:

Do radios use MP3?

This format is similar to the MiniDisc concept, but unlike DAT, MP3 works by deleting data. It is good to know that almost all radios currently use this format. All tubes are stored on a server and programming of the songs to be broadcast is done by computer. When the time comes, the computer searches for sound files with the extension .MP3 on the server and a decompression card automatically converts them into classic CD-quality sound files that are broadcast over the air. Now we can say goodbye to the old days when we were looking for vinyl records in the archives. It is a revolution in the world of radio!

Why the MP3?

Thanks to Mp3 it is now possible to store more than a hundred songs or more than a dozen albums on one blank recordable CD. Not long ago, it was not possible to play MP3 files only on computers, because playback requires real-time decompression that is not compatible with current audio CD playback devices. But given the possibilities this new format offers, Mp3 is on the rise with the public and manufacturers of computers and hi-fi equipment. Diamond Multimedia, famous for its graphics cards, designed the first MP3 player called “Rio”, which is barely bigger than a calling card !!! It allows you to store about 60 minutes of CD quality MP3 in the mass memory and about 9 hours of music if you choose the lowest quality. But many other models come out today with increasing capacity and lower costs … A DVD player in the living room is now also available and suitable for MP3 playback. The advantage is that you can create your own music compilation (MP3s are downloaded from the computer to the portable player through the serial port. Therefore, the songs can come from different sources (such as audio CDs or the Internet).

Are record companies afraid of MP3?

The arrival of Mp3 on the international market is likely to scare record companies, who think their profession will deteriorate and will probably disappear! We know that the copies were already possible with the cassette, the mini-disc and the CD … But it is true that the web is becoming a real database of illegal MP3s. Most artists believe that MP3 is a new way to publicize their works, especially since they can reach a wider audience via the Internet. The solution would be to pay Mp3 on the world network, according to record companies. We still don’t know when, but it is planned. Obviously, this format is not designed to be copy-protected. Many safe formats of comparable quality to MP3, such as “Liquid Audio”, are already offered, but less known, their future may not be very promising. The MP3 format raises the copyright problem as it can be downloaded for free on the internet, so there is some panic on the part of the music industry.

What is an MP3 audio file and how does it work?

MP3 is a method of compressing audio files that uses the MPEG standard to reduce the size from 10 to 12 while maintaining audio quality comparable to a CD. MP3 files are usually used to store a song or the entire CD and require very little hard disk space.

Because of the small file size, a computer can store hundreds or thousands of titles. Therefore, a 30 megabyte audio file recorded in uncompressed form from a CD is reduced to approximately 3 megabytes after “compressing” in MP3. When you download and play the MP3 file, it sounds almost like the original file. If you want, you can download an MP3 file, expand it to its original size, and then burn it to a recordable CD so that you can play it on a CD player.

All it does is toggle between different formats for easy downloading. MP3 compression works with a formula that, among other things, tries to eliminate some noise or frequencies that cannot be heard by the human ear. This method is commonly known as perceptual coding or psychoacoustic modeling. The remaining audio information is recorded spatially efficiently using the MDCT and FFT algorithms.

If we compare CD-quality digital audio, the compression achieved in an MP3 format is about 74%. For example, an MP3 file encoded at a constant bit rate of 128 kbit would produce a file that is approximately 10% the size of the original. For this reason, you can easily transfer a thousand songs in MP3 format to a USB stick, which would not be possible with songs in WAV format. Unfortunately, the benefits of this reduced file size come at a price. The quality of the MP3 title is not as good as the original due to the way the song is compressed.

The quality of an MP3 file depends on the so-called “sampling rate” or “bit rate”. MP3 bit rate The bit rate of an MP3 (or the sampling rate) refers to the amount of audio information (measured in Kb kilobits) that is played back per second. The higher the bit rate, the better the quality. Increasing the bit rate also increases the file size. The higher the quality, the less it can fit on the storage device.

There is a noticeable difference in the sound quality of MP3s with variable bit rates, especially when the file is played on a hi-fi audio system at high volume. If you compress MP3s yourself, it can be helpful to experiment with the bit rate to get better quality or more MP3 playback on your storage device. A good compromise between quality and file size is 192 kps. With this bit rate we get songs with a quality that is very similar to that of CD.

We can only tell the difference to a CD with high-quality headphones or hi-fi systems. On the other hand, if we want better quality, we should opt for FLAC files, ie an audio codec with lossless data compression, ie without loss of quality.

MP3 – Everything you need to know about mp3

The phenomenon of MP3 has revolutionized the Internet world, which has not been the same since then.
Never before have you seen a format that reduces an audio file from 40Mb to 4.
Truth be told, there was something similar, but the quality was not comparable to that
that the mp3 could achieve. But how the heck does this popular format called MP3 work?
This technology caused record companies to lose billions and save tens
(hundreds) of euros for us users?

The magic of the MP3 format.

Well, most of this “magic” resides in a science called psychoacoustics and a series of
very complicated mathematical calculations.
Uncompressed audio and CD audio store more data than our brains
can process and perceive. For example, if two notes are very similar and are together, your brain
you will receive only one of these. If there is a strong and weak sound, your brain will hear the loudest.
then your brain will not be able to hear the smallest sound.
The study of these phenomena and our perception of sound is called psychoacoustics.
MP3 compression technology analyzes sound and breaks it up, comparing it to models
sound included in the compressor itself. Will remove most mismatched sounds
to sound patterns and will keep the ones that match.

The person performing the compression can specify the number of bits to be assigned to each
music second: the higher the number of bits and the less data will be deleted; with some bits in place
More sounds will have to be erased.
This type of compression is called lossy or lossy compression.
MP3 files are made up of a series of very short frames, as in the video, and
Each box is preceded by the header, which contains additional information about the data to come.
At the beginning or end of an MP3 file there is additional information about the file, such as the artist name,
Track title, album, year, genre and comments: This information is called ID3 data (tag).

How mp3 compression occurs.

As is known, the MP3 format eliminates what the human ear cannot hear.
These sounds are removed but there is a small part to not return
“drastic” cut.
But this is only part of the techniques used for compression … first:
the signal is analyzed and a decision is made on how to distribute the available bits, after which it is divided
in sub-bands, processed separately by algorithms.
The available bit rate is calculated, obtaining the number of bits that will be assigned to each frame.
This procedure determines how much audio will be kept and how much will be cut instead.
The frequencies of each frame are compared with the psychoacoustic models contained in the
compressor. From these models, it is determined which frequencies to elaborate with precision,
as perceived by human ear, and which can be partially removed or cut,
since we won’t be able to hear them anyway. Why save what is not needed?
Then the masking effects come into play: if there is a loud sound and a sound
weak it is possible to eliminate the latter, calculating the milliseconds during which it will not be audible.
Similarly, two overlapping sounds (due to intense intensity) or static parts of the sound.
(silence, whisper of sound) are cleverly masked.
Bitrates

How the sound chunks are removed also depends on the bit rate set by the user in
Compression moment. The bit rate corresponds to the number of bits per second used for the
file storage The higher the bitrate, the higher the resolution of the sound.
Imagine a movie: with multiple frames, the image will be fluid, in the same way at a bit rate
greater will correspond to a more complete sound, faithful to the original.

What are the advantages of WAV vs. MP3?

Wave is an uncompressed or lossless format, while MP3 is compressed or lossy. Technically .wav is just a container format and can contain various types of compressed or uncompressed audio, but normally you will see that it contains uncompressed LPCM audio (same as on audio CDs). With .wav files, you essentially get a raw bitstream representation of the audio signal in digital form. An analog sound produced in the real world essentially contains an infinite amount of information because it is a constantly changing wave (see below). To bring these sounds into the digital domain, you need to sample the signal at various intervals to approximate the sound. For .wav, the audio signal is generally sampled at 44,100 times per second or more, and each sampled value is recorded so that the sound wave can be played:

MP3 files are compressed to compress the same audio information into a smaller file size. The .wav format is ideal for very faithful representations of the analog signal, but as you probably know, that usually costs larger files. Compressed audio (and video in a similar way) is designed to reduce file size while maintaining a respectable level of fidelity. In simple terms, compression tries to remove unnecessary data from the stream and reduce the signal to its most necessary components. With MP3, compression and encoding algorithms use a model of how we listen to analyze audio in the frequency domain and remove any unnecessary information. For example, due to auditory masking if there are two sounds at close frequencies, we will often only hear the loudest if the volume difference between the two is significant. So for MP3, the lower volume sound could be ruled out and the audio would sound essentially the same to our ears. Learn more about the technical side of MP3 encoding here.

In practice, both .wav and MP3 have their uses. For production, .wav is the standard because it will almost always be a 100% accurate, bit-by-bit reproduction of the source material. MP3s can be a decent alternative at high enough bit rates. Bitrate is a measure of how many bits per second MP3 encoding will use, which means that the higher the bitrate, the closer the MP3 will be to the original uncompressed stream. Bit rate is generally measured in kilobits per second (kbps). I like the high audio quality for my digital music collection, so when I have a choice, I generally encode MP3 at constant 256 or 320 kbps. That’s the upper end of what MP3s are capable of, and unfortunately a lot of digital music isn’t encoded that high. When the bit rate drops, it can generally be heard first at the high frequencies, for example, the cymbals of a drum kit will sound. 160kbps is tolerable, but somewhat lower than that and you will really start to notice it. But then again, with a high enough bitrate, the differences between MP3 and .wav are barely distinguishable, especially for an untrained listener (most listeners).

For .wav files, we mainly look at the bit depth and the sample rate. Bit depth is the number of bits used to encode each sampled value. The sampling rate indicates how many times per second the audio is sampled. CD (.wav) and MP3 are encoded at a sampling rate of 44,100 Hz (Hertz means “cycles per second”). Newer computers and audio hardware / software are now accommodating higher sample rates, including 48kHz or 96kHz. For .wav, the bit depth is usually 16 bit or 24 bit on newer systems. For most purposes, when using .wav, 16-bit, and 44.1kHz is sufficient, but if you have the capabilities, it’s generally worth upgrading to 24-bit, 48kHz.

Some sample file sizes for a five-minute stereo recording:

.wav, 16 bit, 44.1kHz: 50 MB
.wav, 24 bit, 48 kHz: 82 MB
.wav, 24 bit, 96 kHz: 164 MB
MP3, 128 kbps, 44.1 kHz: 4.5 MB
MP3, 192 kbps, 44.1 kHz: 7 MB
MP3, 320 kbps, 44.1 kHz: 11 MB
FLAC, 24-bit, 44.1 kHz: 28 MB
FLAC, 24 bit, 48 kHz: 31 MB
FLAC, 24 bit, 96 kHz: 61 MB

There is also a variable bit rate option for MP3 encoding, which should offer slightly smaller file sizes for the same quality. It uses a coding scheme that changes (varies) the bit rate for different parts of the song depending on the complexity and how many samples would be needed to faithfully recreate a given section.

Importance of MP3 (digital music)

Music has always been present in societies around the world, and with the passage of time and technological advances it has been enclosed in very diverse reproduction formats: cassette, LP, CD or Mini-Disc have been some of the means Most popular in which people have brought their favorite music.

Software engineering made it possible for Moving Picture Experts Group (MPEG) to design a specific audio format with a .MP3 file extension, a name given by the Fraunhofer Society in July 1995. The MP3 digital audio format would become popular from the second half of the last decade of the 90s thanks to the Internet, P2P networks and the commercialization of the first MP3 players (MPMan and Rio PMP300).

The digital audio format MPEG-1 or MPEG-2 Audio Layer III (MP3) is the most important of all time, even ahead of WMA, FLAC, OGG or AAC, readable by any electronic media player device: televisions, CD / Blu-ray / DVD players, car radios, portable MP4 and MP3 players, PCs, Tablets, mobile phones, compact audio systems, compact music systems….

MP3 music has had a huge impact on modern, hyper-connected society, and has made it possible for people to carry vast music libraries in as little space as on a micro SD memory card.

MP3 quickly moved to CD-Audio, a format that is only capable of storing music with a standardized maximum of 80 minutes of playback and about 20 tracks per CD: the data CD, with MP3 tracks, is capable of storing about 150 tracks per disk (at the rate of 5MB per track).

MP3, with a maximum audio quality of 320KBps and an acceptable minimum of 128Kbps, would conquer digital music lovers and facilitate the “physical” compaction of music libraries: going from individual 80-minute (700MB) discs to discs hard laptops between 250 and 500GB or 8GB / 16GB USB sticks… managing to store thousands of albums in devices smaller than the size of an Apple iPhone.

MP3 would also change the style of music players, in addition to changing to smaller, more versatile and manageable formats. From rough and large portable CD players to tiny devices like iPod Shuffle.

The change from a CD-Audio unit to integrated physical memories or micro SD would also favor the use of music players in sports activities, thus avoiding skipping between tracks due to movement: the new storage medium would solve the typical deterioration of the units optical, with a tendency to scratch in more or less careless use.

MP3 music would dramatically reduce file size, going from around 50MB on CD-Audio tracks (.wav files on PCs) to 5MB or less on MPEG-2 Audio Layer III (depending on encoding quality): It would favor sending tracks by email, sharing them through P2P networks (.torrent), bluetooth or their storage in the cloud (DropBox, BOX…).

The MP3 music format is preferred by the general public, ahead of others such as OGG, FLAC, WMA or AAC: greater diffusion, and better compatibility of the format with consumer electronics devices.

MP3 has also contributed to greater accessibility of music content, its organization on digital devices, management and copying of tracks on computers and mobile devices, and editing of the information attached to each track.

MP3 and its full compatibility in devices commonly used by users has favored legal downloading (online stores, such as iTunes or Amazon) and illegal downloading (download pages and P2P networks).

Thanks to the success of MP3, listening to music on any device with speakers, or to which headphones can be connected, is a simple activity: conventional digital music players (MP4 and / or MP3) are being defeated by Smartphones, with accessible memory of at least 16GB).

MP3 has become the most important and widespread digital audio format of all time.