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Principle of mp3 and file format analysis. Part4

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Principle of mp3 and file format analysis. Part4

The three bytes starting at 1397H are 54 41 47, which store the “TAG” character, indicating that this file has ID3 V1.0 information.

The 30 bytes starting at 139AH store the name of the song, the first 4 bytes that are not 00 are 54 45 53 54, which means “TEST”;
the 4 bytes starting at 13F4H are 04 19 14 03 and the year of storage is “04/25/2003” ”;
the last byte is 4E, which represents the music category, and the code name is 78, that is, “Rock&Roll”; the
other bytes are all 00, and no information is stored.

4 Conclusions
As an important multimedia data type, people are always looking for more efficient compression methods and new sound file formats. In the MP3 file, the MDCT transform is used, which is a quasi-optimal transform with a simple structure and easy programming, which avoids the problem that the optimal transform (KL) is difficult to solve for the eigenvalues and eigenvectors of the covariance. matrix.

Through the analysis of the MP3 file format, it is not difficult to find its shortcomings. Each frame of an MP3 file has the same 4-byte frame header, which requires some space overhead for an MP3 file with a large number of frames. ID3 stores the music description information. The proprietary, copyright, and other information in the frame header is also description information. The music description information is a bit messy.

In any case, the development of MP3 is unstoppable. MP3 has become a recognized sound data format. MP3 is becoming a hot spot in the field of multimedia information processing along with JPEG images and PDF documents.

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Principle of mp3 and file format analysis. Part 3

The ID3 standard MP3 frame header does not consider storing complex information such as song title, author, album name, year, etc., except some simple music description information such as privacy, copyright and original, which are very necessary in MP3 applications.

In 1996, in the “Studio 3” project, FricKemp proposed to add description information for storing songs at the end of the MP3 file and formed the ID3 standard. Until now, ID3 V1.0, V1.1, V2 .0, V2, .3 and V2.4 standards have been formulated. The higher the version, the richer and more detailed the relevant information is recorded.
The ID3 V1.0 standard is not complete and the information stored is too small to store lyrics, album covers, images, etc. V2.0 is a fairly complete standard, but it brings difficulties in writing software, although there are many people in favor of this format, very few are actually implemented in software. The vast majority of MP3s still use the ID3 V1.0 standard. This standard uses the last 128 bytes at the end of the MP3 file to store ID3 information. See Table 3 for instructions on using these 128 bytes.
Table 3 Final ID3 V1.0 File Description
length in
byte (byte) Description
1-3 3 Stores the “TAG” character, which indicates the ID3 V1.0 standard, followed by the song information.
4-33 30 Song name
34-63 30 Author
64-93 30 Album name
94-97 4 Year
98-127 30 Notes
128 1 MP3 music category, a total of 147 types.

3.3 File example
Open a file called test.mp3 in VC++ with the following content:
000000 FF FB 52 8C 00 00 01 49 09 C5 05 24 60 00 2A C1
000010 19 40 A6 00 00 05 96 41 34 18 20 80 08 26 48 29
000020 83 04 00 01 61 41 40 50 04 00 C1 2 41 50 64
…
0000d0 Fe FF FB 52 80 01 EE 90 65 6E 02 30
0000E0 32 0C CD CD CD CD 46 16 41 89 B8 408 89 300 408
0000F0 33 B7 00 00 01 02 FF FF FF F4 E1 2F FF FF FF FF
……
0001A0 DF FF FF FF FB 52 8C 12 00 E 01 FE 90 58 6E 09 A0 02
000150 8513 B0 AC 45 F6 19 61 26 26
0001C0 05 AC B4 20 28 94 FF FF FF FF FF FF FF FF FF FF
…
001390 7F FF FF FF FD 4E 00 54 41 47 54 45 53 54 00 00
0013A0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
001400
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00
001410 00 00 00 00 00 00 4E
File length is 1416H (5.142K), frame header is: FF FB 52 8C, converted to binary:
11111111 11111011
01010010
10001100T

Principle of mp3 and file format analysis. Part 2

MP3 uses perceptual audio coding (Perceptual Audio Coding) this 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. The MP3 encoding and decoding process is shown in Figure 1.
2.4 Modified Discrete Cosine Transform The cosine transform
Modified Discrete CT (MDCT) refers to converting a time-domain data set to frequency-domain data in order to know the changes in the time domain. MDCT is an enhancement of the DCT algorithm. The first fast algorithm is fast Fourier transform (FFT), but FFT has complex operations, MDCT are real operations, easy to program.
When compressing audio data, first divide the original sound data into fixed blocks, and then perform direct MDCT (direct MDCT) to convert the value of each block into MDCT 512 coefficients. The 512 coefficients are restored to the original sound data, and The original before and after sound data is inconsistent because redundant and irrelevant data is removed during the compression process. The FMDCT transformation formula is:
k=0, 1,
.
n0=(N/2+1)/2, X(n) is the time domain value, X(k) is the frequency domain value. If N takes 1024 points, it becomes 512 frequency domain values.
The IMDCT transformation formula is:

n=0, 1, …, N-1
MDCT itself does not compress data, it simply maps the signal to another domain, and quantization compresses the data. When bit allocation is done on the quantized transformed samples, the entire quantized block must be considered the smallest, which is called lossy compression.
3 File Format Analysis
MP3 MP3 file data is made up of multiple frames, and the frame is the smallest unit of the 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.

Principle of mp3 and file format analysis.

Principle of mp3 and file format analysis

1. Introduction
With the rapid development of file compression technology, MP3 has become the most popular music format today. High-quality music spreads rapidly around the world with the arrangement of 0 and 1, which shakes people’s hearts. What is MP3? The full name of MP3 is MPEG Audio Layer 3, which is an efficient computer audio coding scheme. It converts audio files into smaller files with an .MP3 extension with a higher compression ratio, basically maintaining the sound quality of the original file. MP3 is part of the ISO/MPEG standard, which 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”, and has now formed MPEG Layer 1, Layer 2, Layer 3 three audio encoding and decoding schemes. MPEG Layer 3 compression ratio can reach 1:10 to 1:12, 1M of MP3 file can be played for 1 minute and 1 minute of CD-quality WAV file (44100Hz, 16bit, dual channel, 60 seconds) occupies 10M space, so Calculated, the playing time of a 650M MP3 disc should be more than 10 hours, and the playing time of a CD of the same capacity is about 70 minutes. The advantage of MP3 is that the CD is incomparable.
2 Analysis of the principle of MP3
2.1 audio standard
MPEG MPEG (Moving Picture Experts Group) is a group of dynamic picture experts under ISO, the MPEG standard which makes it widely used in various multimedia. The MPEG standards include audio and video standards, of which the audio standards have been established as MPEG-1, MPEG-2, MPEG-2 AAC, and MPEG-4.
The MPEG-1 and MPEG-2 standards use the same family of audio codecs: Layer 1, 2, 3. A new feature of MPEG-2 is the use of low sample rate expansion to reduce the data stream, and another feature is multichannel expansion, which increases the number of main channels to 5. The MPEG-2 AAC (MPEG-2 Advanced Audio Coding) standard was released by Fraunhofer IIS and AT&T in 1997 to significantly reduce data traffic. The MDCT (Modified Discrete Cosine Transform) algorithm adopted by MPEG-2 AAC has a sampling frequency between 8KHz and 96KHz, the number of channels can be between 1-48.
The three layers of MPEG Audio Layer 1, 2, and 3 use the same filter bank, bitstream structure, and header information, and the sampling frequency is 32KHz, 44.1KHz, or 48KHz. Layer 1 is designed for DCC (Digital Compact Cassette) compressed digital tape, the data rate is 384kbps, Layer 2 has made a compromise between complexity and performance, and the data rate is reduced to 256kbps-192 kbps. Layer 3 is designed for low data traffic from the start, and the data traffic is 128Kbps-112Kbps. Layer 3 adds MDCT transformation to make its frequency resolution 18 times that of layer 2. Layer 3 also uses average information similar to MPEG video. Entropy Encoding reduces redundant information. The vast majority of MP3s use the MPEG-1 standard.
2.2 Purpose of audio compression
The MP3 format began in the mid-1980s, when the Fraunhofer Institute in Erlangen, Germany, dedicated itself to encoding high-quality, low-data-rate sound. Let’s look at an example: you want to sample a song you like that is about 4 minutes long, store it on a disk, sample it in CD-quality WAV format, at a sample rate of 44.1 kHz, that is, receive a value of 44100 per second, stereo, each sampled data is 16 bits (2 bytes), so the space this song occupies is:
44100 x 2 channels x 2 bytes x 60 seconds x 4 minutes = 40.4 MB
If you download this song from the Internet, assuming the transmission speed is 56 kbps, the download time is:
40.4x106x8/56x103x60=96 minutes
Even a 1M broadband network requires more than 5 minutes, it can be seen that audio compression is particularly important to reduce audio data storage space.
2.3 Encoding and decoding
MP3 MP3 audio compression consists of two parts: encoding and decoding. Encoding converts the data in a WAV file into a highly compressed bitstream, and decoding takes the bitstream and reconstructs it into a WAV file.

THE MOST COMMON FORMATS FOR MUSIC AND OTHER AUDIO FILES AND HOW THEY ARE RELATED TO EACH OTHER PART 2

AUDIO CONVERTER

With an audio converter the situation is even simpler. Programs of this type are specially designed to convert between audio formats quickly, without explicit user intervention. Unlike audio editors, converters, we can say, use batch mode, that is, they allow you to convert MP3 files in a single operation, for example, not a single copy, and make several pieces at once. Depending on the app’s function, there may be dozens or hundreds.

Audiobooks in MP3 format

Once again, the operation of such a package is simple. Just select the source material (usually it can be a completely different file type) and install the final format. Then press a special button to start the process, the output user gets all files of a certain type. Your save usually occurs in the folder set in the app’s default settings, but the save location can of course be changed by yourself. By the way, the same applies to basis functions, which will be used during the transformation. However, any program initially provides the user with a specific set of criteria to use with a specific type of audio file. They can also change.

The beauty of these apps is that they have a complete process that will automate as much as possible and do all the required processes without much time. However, if we use a music or audio editor, comparing them in terms of improving the same sound quality especially cannot be dispersed here.

MUSICAL ARRANGEMENT
This is another type of software, most of which have built-in editors for MP3, WAV, etc. In this sense, they work on a similar principle to audiorekatorami, but their abilities are slightly broader.

Convert to MP3 format

First of all, it deals with the fact that the entire composition can consist of fragments of different types (MP3, MIDI, WAV, OGG, VST-library or DX-tool, etc. D.). After recording all sound tracks, for example mixing and mastering with virtual synthesizers or prescription parties, the resulting files can be saved in the desired format. Mostly it is an MP3 or WAV, or the program’s project file. In some applications, there is also a recording function to disk. Do you want an audio CD? No problem! In addition to the audio editor, it may take a few minutes to perform the necessary operations and get the tracks on the output disc in CDA format.

If we talk about the benefits of this type of application, it is obvious that only a few formats of the same union, and then saving or exporting to some of the most common are its greatest advantages. Also, you need to pay attention to the fact that the very overlay effect or change of any track parameters happens in real time, that is, the result will not necessarily wait; can be heard immediately by turning some knobs, for example. , or another option. Of course, this is only a small part of what packages are capable of.

HOW SHOULD I USE IT?
Finally, we come to the question of choosing the software to use with the MP3 format, or any other sound to record to. As is clear, normal listening to music or audiobooks is enough and a humble player (software or “iron”), or more commonly a DVD player.

Converting files to other formats, so to speak, in a hurry, is the perfect audio converter. However, if the output needs to achieve crystal clear sound quality, or even convert one file type to another, it is indispensable without powerful dedicated software. Of course, this requires ordering more, and without any experience, time to get the same high-quality MP3 files as the first time and you can’t get. However, with at least some in-depth study from audio editors, let alone professional music studios, the results will exceed everyone’s expectations.

THE MOST COMMON FORMATS FOR MUSIC AND OTHER AUDIO FILES, AND HOW THEY ARE RELATED TO EACH OTHER

And for the direct competitors of the universal MP3 format, they can count on a lot today.

Due to continuing inconsistencies in home storage of the WAV format, it was eventually discontinued. But for professional studios, he says, the basics of the job. Especially when recording live vocals or instruments. Just convert the recorded material from WAV to MP3 at the final stage.

music format

However, music can be represented in some other popular formats nowadays. For example, many times (especially the Internet) they use these data types like OGG, AIFF, AMR, etc. But the real competitor of MP3 has become the newest and best audio FLAC etc. Of course, for MP3 you can convert all parameters to the maximum, but the playback quality of FLAC represents much higher. Also, it is a single file and the separation occurs directly on the track due to the player or startup software. In other words, listeners see each track individually, but can switch between playback tracks. For the MP3 format, this also seems possible to merge multiple tracks through it, thus creating a single file. But here it is in this version fast switching between tracks will not be possible (normal fast forward should be used, that’s all).

However, not everything is bad. The fact that music or audiobooks are all popular formats today allows them to be easily converted, even keeping the original parameters of the audio material. Based on this, and for sound processing and conversion and audio editors, almost all programs call converters. Any program of this type (MP3 editor or converter) detects the original and final type of audio files, is unambiguous and can produce direct and reverse transformations. Let’s explain this specific example.

WAVE THEORY AUDIO EDITOR FOR MP3 FILES
Many types of software are used in audio processing today. First, look at the narrow application of so-called audio editors. The most prominent representatives of these can be called giants Sony Audio Forge, Sintrillium Cool Editing Pro, which was later acquired by Adobe and renamed Audition, Acoustica Mixcraft, ACID Pro and many others.

mp3 editor

The principle on which they operate is that, for convenience, all MP3 audio programs have a typical waveform, as originally used for WAV files. This method determines the appearance and opportunity enough to edit any type of conventional audio material in WAV format. Other than that, the fact that you can do basic copy, cut, paste, etc. E., it’s just a matter of getting the frequency characteristics and bitrate changes, not to mention using a lot of extra effects that plug into VSTs via DirectX or a generic host bridge studio thing.

In its simplest form, the conversion can be done using the standard file menu, which contains the line “Save As…” (Save As…) or the export function present in MP3 format. Thus, all the process is reduced to just the final selection of the format (MP3 here as an example) and activation of the recording mode. In this case the conversion will be done automatically saving the current configuration parameters and the frequency characteristics. I don’t like the original version? ?Nothing is easier than changing the format to MP3, pre-specified with higher settings. However, one thing needs to be considered here: if the raw material is of such poor quality that special remediation or even professional tools will not work for audio it is necessary to use Repairs here, the intervention of various filters, etc. D. For the layman, it will cause great difficulties.

As is clear, there is absolutely no difference between the audiobooks we are dealing with: MP3, music or just recorded voice or noise. By the way, audiobooks are supposed to have a much lower sound quality by default. This is understandable, since the file has to take up minimal space and, in general, the perceived sound characteristics of speech are not that important. Finally, is this a professional recording of a particular set of albums?

However, if you use some standard operations, even without specific knowledge, it’s fine to achieve good results, especially since there are such built-in templates, based on any application for specific operations. Of course, it will be very difficult for the first time to achieve a perfect sound, but if you study the plan and understand how it works, it will work like clockwork, and as a result, it will take a lot of time.

What audio format should I choose?

What audio format should I choose?

Best Audio Format
Everybody loves music. Some listen to it on the way to work, and others can’t go a minute without their favorite songs. Listening to music comfortably depends not only on the mood, the time, the moon phase and good headphones, but also on the audio format in which it is stored on our devices.

In the 21st century, streaming services are becoming popular, but most people still store music offline and listen to it from their phones, players, audio systems, etc. But this post is not a discussion “Which headphones are better?”, “Why listen to music?” or “Why vinyl, not CD?”, but a brief summary of today’s most popular digital audio formats, their pros and cons. I will not analyze them all, and I will not compare different encodings, the differences “this AAC from this AAC”, but I will try to count in an accessible way the differences of some popular audio formats from each other.

So what is the best way to store your music collection? Today, there are many digital audio formats, and if you want, you can see a list of them on Wikipedia. But we will focus only on MP3, AAC, WMA and FLAC.

MP3

The most popular audio format and nobody can argue with that. Why is it so popular? It’s simple, because Mp3 was the first audio format with the best ratio (at the time) of file size and quality when compressed. Therefore, most of the songs were translated into MP3, which served as the undisputed primacy of the audio format on the market.

The advantages are clear from the previous paragraph: small size, tolerable compression loss, ubiquity, compatibility with all devices, and also, due to the small size, you can store a large collection of songs on a medium with little memory capacity, which it is also an advantage for some.

But Mp3 also has some disadvantages. Even though compression losses are not visible to ordinary people, knowledgeable people will notice them immediately. This is a low sound quality compared to other audio formats, as well as a “cut” of frequencies above 17 kHz, which is felt by ear with good headphones.

AAC

The young audio format AAC, mainly promoted by Apple, can be considered the successor to Mp3. AAC seems much more advantageous because Compared to MP3, AAC file compression is more efficient. At a bit rate of 128 kbps, an AAC composition is comparable in sound quality to the same MP3 composition at a 192 kbps bit rate.

Better compression quality is a major advantage of AAC. The disadvantage is not the same prevalence as in the same mp3. Some devices do not yet support this format. And also the compositions in AAC take up more space than in MP3. Not as much as FLAC, but still, for some it is a critical factor.

WMA

The WMA format was created by Microsoft as an alternative to Mp3 for Windows users. It was believed that with half the bit rate of MP3, WMA produces similar quality. But, in fact, the composition in WMA at 128 kbps is noticeably lower than that of Mp3. The advantages include full Windows support, but the disadvantage is extremely low quality at a low bit rate. By personal observation, I will say that I have not seen people storing their music in this audio format for a long time.

FLAC

One of the most common audio formats for music lovers in good quality. FLAC compresses the data, leaving it in the output identical to the original, without losing any data, which is the main lossless compression algorithm. Furthermore, decoding the FLAC format does not require as much processor resources, allowing you to listen to music on portable devices.

The advantages of music in FLAC are excellent quality and fast decoding, but a disadvantage, as a result, is the large file size.

So in what audio format should you keep your music collection? If you are not so critical of losses after compression, if you want to make a mistake with the support, so that your collection does not become a bunch of useless files in 5 years, you have a limited amount of memory for your music, then choose Mp3. If free space allows you to store larger files, switch to AAC. I personally don’t recommend WMA. I think this audio format is dead, although most people will not agree with me. And if quality is important to you, you have a good audio system or headphones, and even minimal compression loss is inexcusable for you, then FLAC definitely is. But be prepared for the fact that you must have plenty of room for music.

The best popular audio formats

The best popular audio formats

I looked around the forest of audio formats for normal use and chose the 5 most important ones. It is true that, in part, a bit simplified, a bit rough in presentation. I refrain from differentiating the exact settings of the respective codecs, that would be too complex.

I also don’t want to get into the nasty topic of DRM. The most important one I dropped is probably Vorbis. . Of course, I assume that the correct settings are used when encoding and that a high quality level is selected.

1st place:
MP3 (MPEG-1 Audio Layer 3)

The most widespread digital format, with good encoding (for example, with LAME) in high bit rates, a format of the highest quality and transparency.

Quality (4.5 / 5 points)
Popularity (5/5 points)
Compression (4/5 points)
Total: 13.5

2nd place:
AAC (advanced audio coding)

It became famous especially for its use in the Apple iPod, a codec that has small advantages over MP3 at low bit rates due to technical developments.

Quality (4/5 points)
Popularity (4.5 / 5 points)
Compression (4.5 / 5 points)
Total: 13

3rd place:
WMA (Windows Media Audio)

Windows proprietary format. Of course, Microsoft has the reins here, so variable format doesn’t run on all playback devices. Otherwise, no major strengths and weaknesses and, for example, the standard format with Napster.

Quality (4/5 points)
Popularity (4/5 points)
Compression (4/5 points)

Total: 12

4th place:
FLAC (Free Lossless Audio Codec) !!

As the only lossless codec on this list. FLAC works in something like a ZIP program: the original can be restored from the compressed file by approximately 50% without restrictions. In times of low hard disk space, a real alternative, especially since many playback devices can play this format. My winner of hearts, the popularity will certainly increase in the future.

Quality (5/5 points)
Popularity (3.5 / 5 points)
Compression (3/5 points)

Total: 11.5

5th place:
Wav

The original format of the normal audio CD data. Impeccable quality and still widespread thanks to the well-known compact disc. It actually started out of the competition because it’s completely unzipped.

Quality (5/5 points)
Popularity (5/5 points)
Compression (0/5 points)
Total: 10

All about all audio file formats

Dematerialized music has evolved considerably for almost 15 years and has played an important role in the daily life of every individual. We’ve all heard more or less about FLAC, MP3, WAV, etc.! Few people really know the difference between each size, its pros and cons …

This article is intended to enlighten you to make the best possible choice for extracting and compressing your audio files.

There are different types of layouts that can be grouped into several large families:

– uncompressed files

-lossless compressed files

– Lossy compressed files

audio formats

-Uncompressed files

WAV: WAV (Waveform Audio File Format) is an audio file format created by Microsoft for Windows. This format is usually an uncompressed container. Therefore, an audio CD with a duration of about 80 minutes in WAV weighs plus or minus 800 MB

Advantages: the file remains in its original form, no loss of information (no loss)

Disadvantages: The WAV file is an uncompressed format that gives it a large size and therefore takes up more space in the storage space.

AIFF – Audio Interchange File Format (AIFF) is the Mac OS equivalent of the WAV format. Therefore, it has the same characteristics as this. The pros and cons of this format are the same as for WAV.

– Lossless compressed files

FLAC: The FLAC (Free Lossless Audio Codec) format is without doubt the most beneficial file for the user. Firstly, in terms of WAV and AIFF, this format is a lossless format, ie the digitization of the file does not imply any loss of information from the audio spectrum. The file is scanned and returned as is. The second advantage of this format is the size it occupies in the storage space. Nondestructive compression is applied to this type of format as a ZIP file, making the scanned file about 2 times less space than a WAV file. Therefore, for 80 minutes of music on CD, the occupied space will be approximately 400 MB. Finally, this format is universal, compatible with most multimedia players, it is compatible with all operating systems except iOS,

Advantages: file size, identical reproduction of the original file during scanning, free and compatible with almost all media players and operating systems

– Disadvantages: none

ALAC: The ALAC (Apple Lossless Audio Codec) format is simply the Apple equivalent of the FLAC file.

– Lossy compressed files

MP3: The MP3 format (Mpeg Layer 3) is a well-known format. It is a format with destructive compression, that is, a recording from which musical information has been removed thanks to the so-called psychoacoustic compression algorithm (taking into account the peculiarities of the human ear), so that less scanning is needed to create a lighter file to obtain . This format is most commonly used for dematerialized music, as it allows a significant space saving in the storage space with a size of about 150 MB for an 80 minute CD. Compression can be more or less destructive depending on the speed used, which can range from 4: 1 (320 Kbits / sec) to 12: 1 (128 Kbits / sec).

-Advantages: it takes up little space on the hard disk and does not affect the quality of the songs with a dynamic range and a limited variety of timbres

– Disadvantages: paid MP3 license, destructive compression for “richer” songs.

AAC: The AAC (Advanced Audio Coding) format is a format close to the MP3 format, but provides additional definition with an identical compression rate. Apple uses this specific format in the iTunes Store, but also on YouTube. the extension can be written in various forms, such as .AAC, .M4A or MP4

-Advantages: better compression quality than MP3

-Cons: compressed file format at a loss

Which format for digital music should you choose?

AAC, MP3, MP3 Pro, Ogg Vorbis, WMA. In the digital age, choosing one or the other of these standards is not easy. Especially since their properties lend them to one use instead of another. Detailed review

Which format for digital music should you choose?

MP3 is far from alone in the world. Feeling that compressed digital music is likely to change the record market, many developers have begun designing formats designed to offer the best compromise between the amount of data used and the sound quality. Thus, AAC for Apple, WMA from Microsoft and other OGG Vorbis communities were born. So many standards that have their advantages and disadvantages and that it is advisable to know them well before choosing the most appropriate coding software for your needs.

First, remember that an audio CD uses uncompressed data. Music is digitized on its surface at a rate of 44,100 samples per minute. Second, each of these samples is encoded in 16 bits (2 bytes) and in stereo. This gives a total of 176 KB per Second music, or about 10 MB per second. Minute. Even if an increasing number of Internet users use broadband, websites that sell music for download cannot afford to offer 40-minute four-minute songs. Compression formats allow this amount of data to be shared by a factor ranging from 8 to 15, with little or no loss of quality.

All of these compression algorithms work on the same principle: eliminate frequencies that the human ear does not perceive at all, or very little, and level the frequencies close to each other for identical values to increase compression. These are the so-called “destructive” algorithms. In other words, when converting a compressed audio file from an audio CD to an audio CD format, the resulting data will not be the same as the original file. Depending on the formats and needs, compression may be more or less important. It is defined by what is called bitrate, that is, the flow of information per. Second of music. It can range from 32 kbps (kilobits per second) to 320 kbps. Detailed review of the different formats.

MP3

Commonly designed by the Fraunhofer Institute and Thomson and standardized in 1992, it is a derivative of audio compression used for MPEG-1 format videos (MP3 also stands for MPEG-1 Audio Layer 3).
This is the format offered by the main configuration panel. In fact, we can define a bit rate (“bit rate” in jargon) that ranges from 32 to 320 kbps. From 128 Kbps the sound quality becomes enough to encode songs. At 192 Kbps, the quality is similar to an audio CD. At this compression rate, one minute of music equals 1.4 MB of data. But it is also possible to choose a variable bit rate called VBR (variable bit rate). In this case, the encoder increases the compression ratio in less complex music regions, reducing the size of the final file slightly. The benefit depends largely on the type of song: 5 to 10% with an extract from classical or jazz music, not much with rock or rap.
The great advantage of MP3 remains its compatibility with all portable audio players, but also certain hi-fi systems, car radios and DVD players in the living room. Almost universal, it appears on all free download sites such as Kazaa or eDonkey. On the other hand, this format sinks slightly at the level of high frequency recovery and is therefore less suitable for e.g. Classical music.
Free MP3 encoding software includes WinAmp and MusicMatch JukeBox. Lastly, note that there are several MP3 coding algorithms, with “Fraunhofer” being the most widely used, and “Lame” being the most effective, with the latter being especially compatible with Pinnacle’s CDex.

WMA

Launched in 1999 by Microsoft, WMA (Windows Media Audio) was only intended to counter the rise of MP3. With compelling arguments. By utilizing the features of the human ear more effectively in the audible spectrum, WMA is able to eliminate frequencies that are truly useless while maintaining certain high frequencies that affect sound quality. The relatively efficient compression algorithm maintains a quality that corresponds to an audio CD with a 128 kbps bit rate, or 1 MB per second. Minute of a song.
Completely free of charge, WMA also has the advantage of having an encoder built into Windows Media Player. An effective way to ensure the spread of this support. Especially since this format is linked to precise copyright management (DRM or Digital Right Management) that allows, for example, to define a limited useful life of files or prohibit recording options. That’s why some music download sites use it. Many digital audio players also support WMA and reputable shareware such as WinAmp allows encoding in this format.

AAC

Contrary to belief, AAC (Advanced Audio Coding) is not a format developed by Apple, but by a consortium that includes the Fraunhofer Institute (father of MP3), Sony and even Dolby. Prestigious names that grow well. In fact, AAC is arguably the most efficient compression algorithm. Unlike MP3 and WMA, it is not based on MPEG-1 but on MPEG-4 (the format behind DivX). This choice seems to have paid off as it allows you to get a better compromise between compression ratio and sound quality. That’s why at AAC we get the equivalent of audio CD quality with a bit rate of only 96 kbps. In addition, as with WMA, the DRM (copyright management) features and the ability to control sounds on 48 different channels,
We found AAC on the Apple iTunes online music site and on your iPod player. But it is also integrated into software like WinAmp.

OGG Vorbis

OGG Vorbis is in audio compression format, as Linux is in operating systems. In fact, it is an “open” format whose source codes are public and can be customized and changed by anyone. It’s still a pretty effective format. At 128 kbps, we reach the quality level of an audio CD (1 MB in 1 minute). The compression structure of OGG format is also significantly different from MP3, WMA and other AACs. Segmenting audio sources into successive packets, the compression algorithm works first on each packet independently of the others. This allows you to not really have weakness at certain frequencies and to maintain the same quality regardless of the type of music.
In addition, polyphony features allow playback of up to 255 audio channels (sic). The package structure also makes it very suitable for streaming on the Internet, especially for online radios. Open, OGG Vorbis needed to evolve quickly and maybe move closer to AAC in terms of performance.