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MP3 digital audio format

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MP3 digital audio format

MP3 File Format

High-quality digitized audio requires a large amount of disk space.

mp3 file

Attempts to reduce the size of files using standard archivers (RAR, GZIP, etc.) do not generate significant gains due to the specificity of the sound data. However, it is possible to achieve a fairly significant level of compression of the audio information using special methods based on the analysis of the data structure and subsequent compression with some loss.

The real possibility of sound processing comparable in quality to existing analog examples did not appear until the late 1980s.

In 1988, the International Organization for Standardization (ISO) formed the MPEG (Moving Picture Experts Group) committee, whose main task is to develop standards for the encoding of moving pictures, sound and their combination. During the ten years of its existence, the committee has developed a series of norms on this subject. As a result, summarizing the extensive research in this area, several specific formats were recommended for storing data, which are excellent in quality of results and data flow.

There are currently three video storage standards: MPEG-1, MPEG-2, and MPEG-4.

Within the first two formats, there are also formats for storing audio information: Layer-1, Layer-2 and Layer-3. These three audio formats are defined for MPEG-1 and minor extensions are used in MPEG-2. The three formats are similar to each other, but use different levels of trade-off between compression and complexity.

Layer-1 is the simplest, it does not require significant compression costs, but it also provides a negligible compression ratio.

Layer-3 is the most time consuming and provides the best compression. Recently, this format has gained immense popularity. It is often called MP3. This name is associated with the extension of the audio files stored in this format.

The underlying idea behind all lossy audio compression techniques is to neglect the subtle details of the original sound that are beyond the reach of the human ear. Here several points can be highlighted.

Noise level . Sound compression is based on a simple fact: if a person is near a loud siren, they are unlikely to hear the conversation of the people who are nearby. And this happens not because a person pays close attention to a loud sound, but to a greater extent because the human ear actually misses out sounds that are in the same frequency range as a louder sound. This effect is called masking, it changes with the difference in volume and frequency of the sound.

The second point is the division of the audio frequency band into subbands, each of which is further processed separately. The encoding program extracts the loudest sounds in each band and uses this information to determine an acceptable noise level for that band. The best encoding programs also take into account the influence of adjacent bands. A very loud sound in one band can affect the masking effect and nearby bands.

Another point of the codification is the use of a psychoacoustic model based on the peculiarities of the human perception of sound. The compression used by this model is based on removing frequencies known to be inaudible, while more carefully preserving sounds that can be easily heard by the human ear. Unfortunately, there can be no exact mathematical formulas here.

The human perception of sound is a complex process, not fully understood, so the choice of compression methods is based on analyzing listening and comparing compressed sounds differently by teams of experts. But here there are practically limitless possibilities in the field of improving psychoacoustic models. Most of the existing algorithms to encode the human voice are based on the high predictability of said signal; Universal MPEG compression algorithms have tried to apply this technique with variable success.

Another compression technique is the use of so-called joint stereo. It is known that the human hearing aid can only determine the direction of the mid frequencies, the high and low sound, so to speak, separately from the source. This means that these background frequencies can be encoded into a mono signal. In addition to all this, compression uses the difference in the complexity of the flows in the channels.

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Why mp3 is enough for you, but Lossless is not necessary

Why mp3 is enough for you, but Lossless is not necessary

mp3

Why mp3 is enough for you, but Lossless is not necessary
Did you finish the greenhouse? So you don’t need to lose, listen to high quality mp3.

Very often there are people who, in principle, despise compressed formats. You should not be guided by your opinion. The following mods that in the studio with a 90% probability will not hear the differences between compressed and uncompressed audio.

MP3 wasn’t invented just to reduce quality. It was developed by the Fraunchhofer Society, an association of applied research institutes in Germany. Later they came up with AAC, which could become the main compressed audio format … But it didn’t work.

Did you know that MP3 comes with variable (VBR) and constant (CBR) bit rate? The constant bit rate, due to the operation of the algorithm, is encoded each time as the first. Therefore, it can produce uneven quality, which means that not all sounds in this situation will be recorded in high quality.

Since MP3 has been around for a long time, it has many limitations. Bit width is 16-24 bits. The sample rate is represented by the following set of options: 8; 11,025; 12; sixteen; 22.05; 24; 32; 44.1; 48. The maximum bit rate does not exceed 320 kbps. The maximum number of channels is 2. But we are still talking about music, we still have to search for multi-channel recordings.

Now let’s see how MP3 is encoded. The illustration shows the time-frequency distribution of sound. Same recording: Audio CD, OGG file, MP3 well encoded. What we observe is that the pieces on the right and left almost completely coincide. This means that the MP3 file sounds almost the same as the original CD recording.

Human hearing and its limits – psychoacoustics

The fact is that the main task of the Fraunchhofer Society is the development of psychoacoustic models of human perception of sound. And here are many subtleties. The main thing is that we are not dolphins.

Second, there are certain restrictions on the number of sounds perceived simultaneously. A person cannot simultaneously hear more than 250 sounds of 24 ranges (in addition, the number of simultaneous sounds in the range is also quite small).

Third, the audible range is 16 Hz to 20 kHz and at the age of 60 it is reduced by almost half. Ideally, and during training (yes, you have to train it!).

All frequencies below 100 Hz are perceived not by the hearing cells, but … by the skin. Then the low waves are reflected in the ear canal; these waves are perceived as infrabass. (This is from the bone conduction area).
mp3_7_resize
Also, the number of cells that register acoustic waves is different for each one. But what is there? For each individual, their number in the right and left ear is different.

By the way, the perception of each ear is different. Change channels of your favorite song – get a new sound.

If you dig deeper, it turns out that each sound frequency is perceived only at a certain volume. When it is reached, the silence is replaced by a sharp and quite different sound. After that, a person can hear a lower sound of this frequency.

Digital audio formats: the MP3 phenomenon

Digital audio formats: the MP3 phenomenon

MP3 format

The MP3 music format (MPEG-1 Layer 3) is one of the most widely used digital audio formats in the world.

MP3 format MP3 format : An Overview

It is compatible with all portable and stationary audio devices. In May 2017, the developers of the format announced his “death”. On April 23, 2017, the Technicolor and Fraunhofer IIS licensed commercial program was canceled: the last patent included in the program expired, making the format standard in the public domain.
Can we say that the days of the most popular format are numbered? MP3 development began in the late 1980s at the Fraunhofer Institute for Integrated Circuits (IIS). In 1987, the University of Erlangen-Nuremberg and Fraunhofer IIS teamed up to work on the EU147 EUREKA Digital Audio Broadcasting (DAB) project. The first result of the alliance’s work was the LC-ATC codec, which made it possible to encode stereo music in real time.

The next step was the development of an optimal frequency domain (OCF) coding algorithm, which already had some of the characteristics of the future MP3 codec. For the first time, it is possible to encode music in good quality at 64 kbps for a mono signal. OCF was the beginning of the path towards standardization MPEG (Moving Picture Expert): an organization, responsible for the development and implementation of international standards for the compression and transmission of digital video and audio content.

In 1989, MPEG received 14 proposals for the implementation of an audio coding standard, so participants were invited to combine their developments. This led to the emergence of four potential candidates, including MUSICAM from the Institute for Broadcasting Technology IRT and Philips and ASPEC (Adaptive Spectral Perceptual Entropy Coding), which is the result of further enhancements to the OCF Fraunhofer IIS in addition to contributions from the University of Hannover in collaboration with AT&T and Thomson.

After extensive testing, MPEG proposed combining MUSICAM and ASPEC to create a family of three encoding methods: Level 1: a low-complexity version of MUSICAM; level 2 – MUSICAM codec; Level 3 (later called MP3): based on ASPEC. Technical development of the MPEG-1 standard was completed in December 1991. In 1994, Fraunhofer IIS introduced the world’s first MP3 encoder, the L3enc, and in 1995 the Fraunhofer researchers unanimously accepted “.mp3” as the file extension for MPEG Layer 3 [1].

Thanks to the compression algorithm used in the MP3 audio format, the size of the data required to reproduce the recording and ensure the quality of sound reproduction is significantly reduced to 10-12 times the original, depending on the recording bit rate. . Bit rate refers to the encoding / decoding rate of a digital audio stream; sound quality improves with increasing bit rate. The MP3 format has the following bit rates: 32 kbps (very low quality, acceptable only for voice), 96 kbps, 128 kbps (medium quality), 160 kbps, 192 kbps, 256 kbps, 320 kbps (maximum optimal quality). The principle of the compression algorithm is as follows: during the compression process, the audio codecs analyze the signals, focusing on the audible fragments, which are saved for later playback or transmission.

This rules out sounds beyond the perception range of the human ear (20 to 20,000 Hz). That is why MP3 is called lossy. There are three ways to encode MP3 files: constant bit rate (CBR), variable bit rate (VBR), and medium bit rate (ABR). CBR is the default encryption mode. In this mode, the bit rate is constant for the entire file. This means that each part of the MP3 file uses the same number of bits. Regardless of the complexity of a piece of music, the encoder uses the same bit rate, so the quality of the final file is variable.

Complex parts will be of lower quality than simpler ones. The main advantage of this mode is that the size of the final files does not change and can be accurately predicted. When encoding in VBR mode, the user selects the desired quality on a scale of 9 (lowest quality, highest distortion) to 0 (highest quality / lowest distortion). The codec then tries to maintain a certain quality throughout the file by choosing the optimal number of bits for each part of the audio recording. The main advantage is the ability to specify the level of quality to be achieved, but the significant disadvantage is the unpredictability of the final file size.

What is an MP3 file?

We start with one of the most common files in the world of computing, that is, the one with the name MP3.

MP3 files have been around for years and that is why their development is so widespread.

But what does an MP3 file represent in practice?

Well, an audio file in general is a sequence of numbers obtained by sampling the analog signal.

MP3

This sampling then responds to some parameters that are the frequency, measured in Khz and the resolution that is instead expressed in Bit.

The MP3 file is the most compressed form of an audio file, so to speak.

At the end of the day, you have to understand that the MP3 file manages to eliminate all the superfluous parts of the digital file of the sequence and the final sampling, exploiting some imperfections of the human body to be able to give you a clear and clean melody.

However, on the other hand, the MP3 file considerably reduces the quality of the reproduced sounds.

In fact, all the different nuances of a given melody boil down to the bone.

An MP3 is small in size from the point of view of memory, it must be seen as a kind of concentrate that gives you an appreciable final result but not one hundred percent complete.

In the most extreme cases, an MP3 file can reduce the original sounds and nuances of the music or melody by up to 90%.

However, these formats are highly appreciated and used because in addition to being practical and straightforward, they are now compatible with any technological device.

This means that you can always carry them with you and any product you have will be able to read an MP3 file.

Mp3 format

MP3 (in full version Moving Picture Expert Group-1/2 Audio Layer 3) is a lossy audio compression algorithm, developed by the MPEG group, capable of drastically reducing the amount of data needed to store a sound, while still be a reproduction. acceptably faithful to the original uncompressed file.

Mp3 Format

Data compression is carried out by eliminating all those sounds that are not perceived by the human auditory system. In fact, recordings in wav format contain much more information than our ear is capable of distinguishing: by removing too much information, it is possible to obtain size reductions of more than 10 times (compared to uncompressed wav format).

In practice, the mp3 format exploits the limits of our auditory system, limits that depend so much on the structure of our ear (not capable of perceiving frequencies above 20 kHz, but particularly sensitive to the intermediate range that goes from 700 Hz to around 6000 Hz) and the ways our brain perceives and interprets sounds. These perceptual limits are studied by psychoacoustics, a sector of psychology that deals with the perception of sounds.

A particularly important and exploited effect in mp3 compression is masking (masking), in which the perception (or less) of a sound is influenced by the presence of another sound. For example, conversation at a bus stop can become completely impossible if a noisy bus approaches: a weaker sound is “masked”, that is, made inaudible by the presence of a louder sound. Masking is all the more effective the closer the two sounds are to frequencies, since our auditory system is unable to discriminate sounds with very close frequencies.

As we have mentioned, mp3 compression is lossy type, that is, it causes irrecoverable data loss and consequently quality degradation. Mp3 encoding allows you to choose how much compression the compression should have, keeping in mind that higher compressions will always correspond to lower sound quality. The quality of mp3 compression is adjusted by a parameter called bitrate that specifies how many kbits the mp3 file should use for each second of recorded audio. There is also the possibility to vary the bit rate within a single mp3 file, using higher bit rates for some parts and lower bit rates for others (for example you can use a lower bit rate for the silent parts or that contain few instruments and use a higher bit rate for more complex parts).

The usable bit rate values are many (from 8 to 320 kbit / s) but 128 kbit / s is considered a good compromise between compression and quality. Knowing the bit rate, it is easy to calculate the size of an mp3 file, since it is enough to multiply this value by the duration of the recording.

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.