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M4A – AAC format and characteristics

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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.

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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.

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