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How AAC works

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How AAC works

AAC Music File Format

Like MP3, AAC is a lossy music storage format. As in the case of the MP3 format, AAC encoding algorithms cut the highest and lowest frequencies, and also actively use the characteristics of a person’s hearing to remove information about sounds that a person cannot easily distinguish when listening to music. . As a result of compression, AAC files do not sound identical to CD-quality files, but in general the algorithms compress the music efficiently enough that most people overlook the fact that it has been deleted. resulting sound information.

AAC Audio Format

Like MP3, the quality of an AAC file is measured by its bit rate. Common AAC bit rates include 128 kbps, 192 kbps, and 256 kbps.

Without going into technical details, here are the reasons why AAC files sound better than MP3s:

AAC encoding uses samples with a wider frequency coverage from 8 to 96 kHz; mp3 encoding uses samples with coverage from 16 to 48 kHz
Up to 48 channels can be encoded, while MP3 encodes 2 channels in MPEG-1 mode and up to 5.1 channels in MPEG-2 mode
Arbitrary bit rates and variable frame lengths are used

Higher algorithm efficiency and simpler filter banks (instead of hybrid MP3 encoding, AAC uses pure MDCT method)
Greater precision is provided when encoding AAC sound using smaller sample sizes, which are equal to 128 or 120 units, while 192 units are used for mp3 encoding. In this case, the smaller sample size allows you to code more precisely, since the original sound wave is an analog signal, and for a more accurate description, it needs to be measured as often as possible. Therefore, a smaller sample size is better because it allows you to more accurately describe the analog nature of a sound wave in digital form.

Sound frequencies above 16 kHz are processed more efficiently. Let me remind you that in mp3 format these frequencies are simply erased
More progressive algorithms are used in stereo binding mode. Let me remind you that stereo stitching allows you not to store both channels separately, as in CD-quality recording. The common signal for both channels is stored and only the difference between the channels is stored separately from each other.
Additional modules were added to improve compression efficiency: TNS, Inverse Prediction, PNS and others
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How AAC works with iTunes

Apple adopted AAC as its primary audio format. All songs stored in iTunes Store and all songs streamed or downloaded from Apple Music are encoded in AAC format. All AAC files in the Apple ecosystem are encoded at 256 kbps.

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What is the AAC format and what are the advantages over mp3?

Designated heir to MP3, it is the most widely used encoding format today. Compatible with YouTube, iPhone and Android, among others

AAC

More than twenty years of honorable career, which have allowed music to become truly “pop” and spread throughout the world, regardless of the playback device you use. This is the rather heavy legacy of MP3, a multimedia format created between the late 1980s and early 1990s by Italian engineer Leonardo Chiariglione. In its place we now find AAC, the audio file encoding standard developed by Bell Labs, Fraunhofer Institute, Dolby Labs, Sony, and Nokia at the beginning of the last century.

AAC

A lossy codec, AAC is considered a standard by both ISO (acronym for International Organization for Standardization) and IEC (acronym for International Electrotechnical Commission) and is an integral part of the MPEG-2 and MPEG-4 specifications. After a few years “in the shadow” of MP3 encoding, today AAC encoding is by far the most widespread and adopted: it is the standard or default audio format for YouTube, iPhone, iPod, iPad, Nintendo DSi, Nintendo 3DS. , iTunes, DivX Plus Web Player, PlayStation 3 and is compatible with PlayStation Vita, Wii, Sony Walkman MP3, Android and BlackBerry.

Differences from MP3 files

The reason for this success is explained by the numerous improvements that this standard presents compared to the one conceived by Chiariglione. First of all, the AAC can guarantee better audio playback quality with the same file size (and therefore bit rate). This is because AAC encoding has a greater variety of samples (8 to 96 kilohertz, as opposed to 16 to 48 kilohertz samples allowed by the MP3 format) and supports a greater number of channels of audio playback (up to 48 channels).

This is combined with the increased flexibility and flexibility of AAC encoding, which allows engineers to design and implement encoding and decoding algorithms according to their needs. This flexibility encourages real competition, leading to more efficient and effective algorithms. Translated into simple words, an audio file converted with an AAC encoder at the same bit rate will guarantee, as already mentioned, better playback quality than many other competitive lossy formats.

What is the AAC?

MP3 has practically become synonymous with online audio, as it is capable of transforming your music into small files, ideal for sharing. However, the fact of having a “reasonable” audio quality displeases many people, opening the market to other more robust formats, such as AAC (Advanced Audio Coding).

AAC (Advanced Audio Coding) Bluetooth Audio Codec

Unlike FLAC, AAC is a lossy audio compression scheme that focuses not on audiophiles, but on users who want high-quality music without sacrificing large disk space or even their portable music players to store them.

Seen by the market as a successor to MP3, this format has big names behind its development, such as Sony, AT&T, Nokia and Dolby Laboratories, and has even been standardized by renowned ISO and IEC institutes. Many of our devices already use AAC as standard, like PlayStation 3 and Portable, Nintendo Wii and DSi, Andoid devices, iPhones and iPod, being the standard format used even in iTunes.

AAC

To explain AAC’s superiority over MP3, let’s look at some points of comparison:

-AAC achieves a higher level of audio quality without increasing file size. This is measured in Kbps (Kilobits per second) and the higher this number, the more transparent the sound will be and the more space will be needed for the file. A song compressed in AAC at 96 Kbps has a clearer sound than an MP3 at 128 Kbps, which means more quality in a smaller size;
-A very important parameter to estimate the “purity” of a song is its sampling frequency, because the higher the margin, the more details are stored. While MP3 has a range of 16KHz to 48KHz, AAC ranges from 8KHz to 96KHz;
An MP3 audio file only supports 5.1 channels in MPEG-2, while AAC is capable of playing up to 48 different channels in MPEG-4;
-The above data only explains the preference of many users and companies to replace MP3, which has been standard since 1993. The only drawback seen by some manufacturers is the need to pay royalties to the Dolby Digital encoder (decoder) and AAC decoder. , but this is something that already happens with the MP3 format, so who knows with a little negotiation things will be resolved.

M4A – AAC format and characteristics

Presentation of the AAC format

AAC (Audio Advanced Coding) is an audio data compression format developed by the Fraunhofer Institute in collaboration with AT&T, Nokia, Sony and Dolby.

As with the MP3 format, it is a destruction of audio data compression, called “lossy compression” (that is, lossy compression), ie the removal of certain auditory information (for example, inaudible frequencies) to the best possible compression rate, keeping a result as close as possible to the original data.

AAC

The AAC format corresponds to the international standard “ISO / IEC 13818-7” as an extension of MPEG-2, standard of the Moving Image Expert Group (MPEG).

The AAC format was chosen by the Apple company as the primary file format on iPods or in the iTunes software.

Frequently Asked Questions: M4A – AAC Format and Features

Technical properties

AAC uses a variable bit rate encoding (Variable bit rate in English, sometimes abbreviated as VBR), that is, an encoding that allows you to adjust the number of bits used per second to encode audio data according to the complexity of current at a given moment. The algorithm used is more efficient than that of MP3, enabling smaller, higher quality files to be obtained, while requiring less resources to encode or decode.

Compared to the maximum of two channels (in stereo) supported by the MP3 format, the AAC format allows polyphonic recording of up to 48 channels. The AAC format also provides sound reproduction in the 8Hz-96.0kHz frequency band, compared to 16-48kHz for the MP3 format.

Files in AAC format, with extension .mp4 (for MPEG-4), .m4a (for MPEG-4 audio) or .m4p (for protected MPEG-4), are generally smaller than files in MP3 format.

AAC Compatibility

The AAC format is not compatible with the MP3 format, this means that you must use a player that is compatible with the format or install a specific codec so that existing players can read files in AAC format.

MP3 y AAC

However, more and more software players allow you to read files in this format, and the latest hardware MP3 players support this format.

What is the AAC format and what are the advantages compared to the mp3?

A designated heir to MP3, this is the most widely used form of encoding today. It is supported, among others, by YouTube, iPhone and Android.

Over twenty years of honest career, which has allowed music to become truly “pop” and spread around the world, regardless of the playback device used. This is the rather heavy legacy of MP3, a form of multimedia created in the late 1980s and early 1990s by Italian engineer Leonardo Chiariglione. Instead, we now find the AAC, the standard for encrypting audio files developed by Bell Labs, Fraunhofer Institute, Dolby Labs, Sony and Nokia near the end of the last century.

Lossy codec, the AAC is considered a model by both ISO (an acronym for the International Organization for Standardization) and IEC (an acronym for the International Electrotechnical Commission) and is an integral part of the MPEG-2 and MPEG-4 specifications. After a few years “in the shadows” of MP3 encoding, today AAC encoding is by far the most common and adopted: it is the standard or default audio format for YouTube, iPhone, iPod, iPad, Nintendo DSi, Nintendo 3DS, iTunes, DivX Plus Web Player, PlayStation 3 and is compatible with PlayStation Vita, Wii, Sony Walkman MP3, Android and BlackBerry.

AAC – Differences with MP3 files

The reason for this success is explained by the many improvements that this model presents compared to the one developed by Chiariglione. First of all, AAC manages to guarantee better audio playback quality for the same file size (and therefore bit rates). This is because AAC encoding has a greater variety of samples (8 to 96 kilohertz compared to 16 to 48 kilohertz samples allowed by the MP3 format) and supports a larger number of audio playback channels (up to 48 channels).

AAC – Portable music player

Added to this is the increased flexibility and flexibility of AAC coding, which allows engineers to design and implement coding and decoding algorithms according to their needs. This flexibility feeds real competition, leading to more efficient and effective algorithms. Simply put, a sound file converted to an AAC encoder at the same bit rate will guarantee, as already mentioned, better playback quality than many other competing loss formats.

How to convert MP3 to AAC

The discussion about converting between MP3 and AAC files is not entirely accurate. While the second is a real audio format used in many areas, the second is an encryption algorithm that can be used by different file formats. The most well-known, in this sense, are “.m4a”, “.mp4”, “.3gp”, “.m4b” and “.m4p”. To convert MP3 to AAC, therefore, you must select one of the forms listed above.

However, converting your MP3 music collection does not require any specific action. You need to select one of the many existing audio conversion programs (or even a special web portal for file conversion) and select the tracks or albums for editing.

AAC audio formats

When we talk about the different audio formats that we have available for our work or entertainment, we usually hear that there is the MP3 format, Dolby type sound, and in some cases it has audio in the AAC format.

This last audio format is very characteristic of some movies found on DVD discs, which comes to be a technical specification that means Advanced Audio Coding, or translated into Spanish “advanced audio coding”, and which actually comes to be an extremely important resource for those editors who work in the video area.

Working with the AAC audio format represents having a better sound quality than many of the cases is distributed to different speakers, perfectly defined in terms of the position they should occupy in an appropriate environment; In addition, this AAC audio format tends to occupy a smaller space than an MP3 audio format would occupy, which in the design of a DVD disc comes to be known as Layer 3 type audio, which is widely used in the compilation of audio and video for the formation of a DVD movie. But the important thing is that this AAC format provides high-fidelity audio quality and that many times it is used for the well-known “no-home” formats.

It is there where the conveniences of using this AAC audio format are found, since by occupying 30% less space than an MP3 audio file, having better quality and fidelity in its sound, it is widely used not only by those film editors DVD, but also by iTunes as well as by many music discs they represent today.

AAC (Advanced Audio Coding) is a digital audio signal computer format based on a lossy compression algorithm, a process by which some of the audio data is removed in order to obtain the highest possible degree of compression, resulting in an output file that sounds as close to the original as possible.

features

AAC uses a variable bit rate VBR, an encoding method that adapts the number of bits used per second to encode audio data, depending on the complexity of the audio stream at any given time. AAC is an encoding algorithm Broadband audio that has superior performance than MP3, produces better quality on small files and requires less system resources to encode and decode. This codec is oriented to broadband uses and is based on the elimination of redundancies of the acoustic signal, as well as on compression by means of the modified discrete cosine transform (MDCT), very similar to that of MP3.

Advantage

Superior audio quality for the same bitrate (kbps) your Radio at 32kbps will sound like 128kbps in mp3. Stereo sound support from 16 kbps unlike MP3 that supports it from 40 kbps. Support on Blackberry, Iphone, Smartphone equipment. Members of the codec family aacPlus aacPlus v1 is the combination of AAC and SBR, as the high-efficiency standardization profile in MPEG-4 (HE AAC). aacPlus v2 builds on the strong success story of aacPlus v1 and adds value in all fields where increased compression efficiency of stereo signals is mission critical. aacPlus v2 is a true superset of aacPlus v1, aacPlus v1 is from AAC. With the addition of Parametric Stereo in MPEG, aacPlus v2 is the current state of the art low-bit-rate open standard audio codec. Not compatible with MPEG-1. Sample Rate: 96 KHz, 88.2 KHz, 48 KHz, 44.1 KHz, 24 KHz, 22.05 KHz, 16 KHz. Maximum quality between 320 and 448 kbps (5 channels) and between 128 and 192 (2 channels) Maximum supported bitrate: From 12 kbps (in HE-AACv2 profile) to 448 kbps (in AAC-LC profile)

Three options

Highest quality (resolution at 23.43 Hz and 2.6 ms) Non prediction Scalable sampling rates

Three types of profiles:

AAC-LC: 16 KBps to 448 KBps HE-AAC: 16 KBps to 128 KBps HE-AACv2: 12 KBps to 56 KBps (most efficient profile in audio quality)

Bitrate or Kilobytes per second (kbps)

What corresponds to talk now is about the quality of these paintings. Let’s take a frame and see its quality and weight in kb … This is called bitrate or kbps which means KiloBytes per Second or Kilobytes per second, and is the measure used to determine the image quality, the higher the bitrate, the image quality will be better, but the weight of the file will be greater too. There are standards and limits for bitrate, this for the MPEG format. For a DVD, which is an MPEG2 video format, the limitation is more than 1500 and less than 8000 kbps, for VCD it is exactly 1150 kbps, and for example a MiniDV tape of a handycam uses a bitrate of over 30000, this is a lot of quality and when you go to hard disk you see the large file size. For the other formats it depends on the codec and its configuration, being able to compare in quality an MPEG2 format with 3000 kbps with an AVI with Xvid codec at 1500 kbps, this difference is given by the way in which the video is compressed, the Xvid codec It does better than the MPEG2 format.

Now, bitrate can be constant throughout the video or it can be adjusted to changing needs, this is Constant Bitrate (CBR) and Variable Bitrate (VBR), when we use Constant Bitrate all video always uses the same amount of information to show Each frame, whether you need it or not, this can make the video heavier than it could be or that it does not have the right quality in certain parts or has plenty of information where it is not needed.

Let’s see the following example, where a small video clip is shown where it requires a lot of bitrate or kbps and another part where it does not need so much, encoded in MPEG CBR and VBR. We see the difference in the weight of the files and their comparison with an Avi with DivX codec with a lower bitrate. In minute 2 another video is shown where very little bitrate is needed and as when coding in VBR or CBR it does not greatly affect the final result.

When we use Bitrate Variable we can define the maximum and minimum to use and let the coding program scan the video and adjust the amount of information as necessary, for this you can use one or two passes (usually no more than two are used), that is, the program goes through the video once, calculates and in the next pass applies the bitrate correctly. It can also be done in a single pass, but the calculation can be wrong, this because to make the necessary bitrate changes makes use of something called keyframes or keyframes. In addition there are programs that detect scene changes and there apply keyframes to change the amount of bitrate occupied, this may be in one pass, but it may also not be as accurate as two passes.

To prevent the file from being excessively complex and heavy to process, when encoding an amount of information is allocated for video blocks, these blocks are defined by the keyframes, for example, there may be 90 frames between each keyframe, and if the video run at 30 frames per second, then the bitrate can change only every 3 seconds of video (3 seconds x
30 frames = 90 frames), and if there is a change of scene, for example, from a dark and slow shot to a scene with light and moving, if we are in the middle of a block between keyframes we will notice that the scene in motion is seen bad, with large video blocks and little definition, this can happen when the coding is done in a single pass using Bitrate Variable, so it is preferred to use 2 passes, in this way the program is responsible for detecting the change of scenes where there is need to adjust the bitrate, and accommodate the keyframes of
correct way, so that in each change the quality of the video is adjusted and seen
all right. And what happens when we have a whole video with movement, well, the bitrate remains high for most of the time, this will make a video that is heavier than another of the same duration but where the content is more static while maintaining good quality . If we use Constant Bitrate for both videos, one with a lot of movement, and another with more static content, the result will be very similar, it will only change the quality of the content, unless we use a very high bitrate to give quality to the video with movement, which it would be excessive for a video of more static scenes, which would generate a heavy file without any need. Therefore, we have videos that can be heavier than others, and videos with different qualities. This is where we need to know what should be adjusted when encoding a video and how automatic adjustments do not always give the same results, this because each video may have different coding needs.

Differences Aac plus vs MP3

When deciding which compression format to choose to take full advantage of own resources such as those of the listener in streaming broadcasts, one of these two alternatives is generally considered.

MP3 or MPEG-1 Audio Layer 3:

It is a standard compressed digital audio format with loss, the loss of information from the mp3 format is not audible by the human ear, therefore we will not distinguish the difference between an uncompressed audio file and an mp3 file.

In addition an mp3 file manages to reduce the size of the sound file without influencing its quality, approximately 1 minute of audio in mp3 format occupies 1 MB with a quality almost equal to the quality of Cd.

These advantages have achieved that the mp3 format can be played in almost all audio players, which is the format par excellence for the exchange through the internet, one of the best options at this time to store music with good quality, and also The audio format that is most used in portable players is a standard and therefore compatibility with all media is guaranteed.

The mp3 audio format allows you to select the quality of the audio that we are going to compress, the quality of cd would be equivalent to 128 Kbps (Bit rate), but we can select the compression between 8 Kbps and 320 Kbps taking into account that the higher the transmission of data (Kbps), the greater the use of broadband resources for both the broadcast and the reception by the listener.

AACplus: MP4 / aacPlus (HE-AAC) Enconder v 1.31; Stereo
As in the mp3, in the aacplus there is a solution for the little width for the channels. This is what is known as “Parametric Stereo” and corresponds to what is known as HE-AAC v2. Unlike what happens in the case of mp3, it is not convenient to use this option in high bitrates, in this case over 48kbps.

Considerations:

Quality assessments are expressed in percentages, with 100% being the overall quality of the original file.
The valuations are merely estimates but are intended to faithfully reflect the differences in quality between the different formats to the different bitrates.
The best alternatives for each format have been marked with red, according to the relationship of quality and consumption of own resources when emitting and resources of the listeners to correctly receive the audio.
Conclusions:

The first and most important regarding the mp3 is that, even in its highest quality, it is already obsolete. In any bitrate it is surpassed by the others so it will always be preferable to perform compression to any other of the subsequent formats. Ogg Vorbis and mpc are better quality formats that far exceed the mp3 but we have not included because they are not widely used. There are also several other formats that offer better compression.
For the mp3 the best bitrate is at 128kbps or 192 kbps, with a minimal difference in quality. Above that the difference is imperceptible and inferior to it is widely discernible.
At 72/74% the AAC PLUS format beats its competitors widely in the 48 / 64kbps being the best choice in the range. It will depend on the original file, as well as the greater or lesser preponderance of the high, medium and low. The decrease in fidelity is easily noticeable but it is not too much and many people will have no problem accepting it.
Under 128kbps, the quality of the mp3 drops considerably, while in the AAC PLUS format the decrease is not as pronounced. In the latter, it can be seen that between 128 and 48kbps the decrease in quality is minimal, with a difference of only 7%. Therefore, it is not worth compressing at 128kbps or at 96kbps having the option of doing so at 48 or 64 with a minimal difference in quality.

Advantages of AAC with respect to MP3

The AAC format supports multichannel sound which is an appropriate audio codec for the surround sound of 6 or more speakers, although it is currently not the most supported codec for it. However, MP3 only allows, in its base format, stereo sound.
It can reach a sampling frequency of 96khz, used in recording studios. MP3 is designed for playback only and to reach up to 48khz.
The sound quality is considerably superior to the same birate. This means that it is possible to encode an audio file in AAC with a bitrate lower than the equivalent in MP3 while maintaining the same sound quality. An audio file in HE-AAC encoded at 48kbps can offer a quality similar to an MP3 encoded at 128kbps.
Even at very low bitrates (32kbps or less) the sound suffers little loss compared to MP3. This could be