What is the Advanced Audio Coding (AAC) Format? An In-Depth Explanation (October 2023)

Introduction to AAC Format

One popular audio file format that provides excellent audio compression is the Advanced Audio Coding (AAC) standard. It is regarded for its effectiveness in providing high-quality sound while keeping a comparatively small file size and is the replacement for the well-known MP3 format.

What is the full form of AAC?

Augmentative and Alternative Communication is represented by the audio file type AAC. Although AAC was originally made available as an international standard in 1997, its creation had started considerably earlier. In an effort to provide a more effective and adaptable audio compression format, the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) developed it.

History of AAC File Format:

Originally intended to be a component of the MPEG (Moving Picture Experts Group) standards, the AAC format was first developed in the late 1980s. The MPEG organization develops standards for both audio and visual compression. The objective was to develop a more sophisticated and effective audio compression technique than the popular MP3 format.

AAC was officially standardized in 1997 as part of the MPEG-2 and MPEG-4 specifications, providing a significant improvement over the older MP3 format in terms of both audio quality and compression efficiency.

What are the Technical Aspects of AAC File Format?

1. Compression Method: AAC employs a lossy compression method, which means it reduces the file size by eliminating some audio data while attempting to preserve the essential audio quality. This compression is achieved through various techniques, including psychoacoustic modeling, which identifies and removes inaudible or less important sound components.
2. Audio Quality: One of the defining features of AAC is its ability to deliver high-quality audio at lower bit rates than its predecessors. The advanced compression algorithms used in AAC result in improved sound fidelity, making it a preferred choice for many audio enthusiasts.
3. Profiles and Levels: AAC comes in various profiles and levels, which determine its capabilities and applications. The most common profiles are Low Complexity (LC) and high efficiency (HE), with LC being suitable for general audio and HE optimized for low bit rates and mobile applications. The levels define the complexity and performance of the AAC codec.
4. Bit Rates: AAC files can be encoded at various bit rates, ranging from low bit rates suitable for mobile streaming to high bit rates that provide near-CD quality audio. The flexibility in bit rates allows AAC to adapt to different use cases.

What are the Multiple Modes of AAC format?

AAC, or Advanced Audio Coding, encompasses multiple modes that cater to different use cases and quality requirements. Each mode offers specific features and serves various applications.

1. AAC-LC (Low Complexity):

Overview: AAC-LC is the most commonly used and widely supported mode of AAC. It's designed for efficient compression while maintaining high audio quality.

Features:

• Good audio quality at lower bitrates.
• Broad compatibility with a wide range of devices and platforms.
• Suitable for streaming and mobile applications.
• Commonly used for music distribution and podcasting.

Differentiation: AAC-LC balances compression efficiency and audio quality, making it an excellent choice for general audio needs.

2. HE-AAC (High-Efficiency AAC):

• Overview: HE-AAC, also known as AAC+, is optimized for streaming and broadcasting, where bandwidth constraints are a concern.

Features:

• Exceptional compression efficiency, especially at lower bitrates.
• Well-suited for streaming audio over low-bandwidth connections.
• Ideal for internet radio and mobile streaming services.
• Support for parametric stereo for even higher compression.

Differentiation: HE-AAC is focused on delivering high-quality audio at very low bitrates, making it the go-to choice for online radio and mobile streaming applications.

3. HE-AAC v2 (Enhanced High-Efficiency AAC):

• Overview: Building upon HE-AAC, HE-AAC v2 further enhances compression efficiency and audio quality, making it suitable for various applications.

Features:

• Improved audio quality at very low bitrates, even better than HE-AAC.
• Support for full-bandwidth audio at higher bitrates.
• Efficient parametric stereo and spectral band replication.
• Widely used for digital radio and mobile TV.

Differentiation: HE-AAC v2 offers superior audio quality at very low bitrates and is perfect for digital radio broadcasts and mobile television.

4. AAC-ELD (Enhanced Low-Delay):

Overview: AAC-ELD is designed for applications where low audio encoding/decoding delay is crucial, such as video conferencing and telecommunication.

• Features:
• Low encoding/decoding delay for real-time communication.
• Good audio quality even at lower bitrates.
• Ideal for video conferencing and VoIP applications.
• Enhanced noise suppression and echo cancellation.

Differentiation: AAC-ELD excels in delivering low-latency, high-quality audio, making it a top choice for real-time communication.

5. xHE-AAC (Extended HE-AAC):

• Overview: xHE-AAC is a versatile mode of AAC, designed to cover a wide range of bitrates and applications.

Features:

• Exceptional audio quality across the entire bitrate spectrum.
• Scalable from very low to very high bitrates.
• Ideal for streaming, broadcast, and multimedia applications.
• Efficient utilization of available bandwidth.

Differentiation: xHE-AAC offers adaptability to different bitrate requirements, making it suitable for a wide range of multimedia applications.

What are the Applications of AAC Audio Files?

AAC has found widespread adoption in a multitude of applications:

1. Digital Music: AAC is a popular choice for digital music distribution. It is commonly used for encoding audio files in formats like M4A (Apple's iTunes) and MP4 (used in various media players).
2. Streaming Services: Many streaming platforms, such as Apple Music and Spotify, utilize AAC for their audio content. The efficiency of AAC allows for smooth streaming even with limited bandwidth.
3. Video Content: AAC is often used for audio encoding in video content. It is the default audio format for YouTube and is compatible with many video codecs, including H.264 (AVC) and H.265 (HEVC).
4. Mobile Devices: AAC is the preferred audio format for mobile devices, including smartphones and tablets. It provides a balance between high audio quality and file size, making it ideal for mobile storage and playback.
5. Broadcasting: Broadcasters also rely on AAC for its efficient compression and audio quality. It is commonly used in digital radio and television broadcasting.

What are the Advantages of AAC Format?

1. Improved Audio Quality: When compared to MP3, AAC offers a considerable improvement in audio quality. Advanced compression methods and better control over high- and low-frequency sounds are used to achieve this improvement.
2. Space-Saving Compression: Because AAC compresses well, smaller files can be created without sacrificing audio quality. Applications like streaming and mobile use, where storage capacity and bandwidth constraints are a problem, will benefit most from this.
3. Flexibility: AAC can accommodate a large variety of bit rates and profiles, making it incredibly versatile. Owing to its versatility, it can be used for a wide range of tasks, from high-fidelity music dissemination to streaming of audio at low quality.
4. Broad Compatibility: AAC is now widely compatible with a variety of platforms and devices. The majority of hardware, operating systems, and media players—including those in Apple's ecosystem—support it.
5. Improved Multichannel Audio: AAC is compatible with multichannel audio, which is essential for immersive audio setups like home theater systems and surround sound.
6. Better Error Resilience: Compared to certain other formats, AAC has better error resilience, meaning that audio can still be decoded more precisely even in the event of data transmission failures.
7. Low Latency: AAC is capable of delivering low-latency audio streaming, which is necessary for online gaming and video conferencing applications.

What are the Challenges and Criticisms around AAC File Format?

While AAC is a widely accepted audio format with numerous advantages, it is not without its challenges and criticisms:

1. Licensing: AAC is subject to licensing fees, which can deter open-source and free software developers from using it. This has led to the development of alternative open-source audio codecs like Ogg Vorbis and Opus.
2. Compatibility: While AAC is widely compatible, there are still instances where certain devices or software may not support it. In such cases, users may need to convert AAC files to other formats for compatibility.
3. Limited Bitrate Savings: While AAC is more efficient than MP3, the savings in bitrate are not as significant at higher bit rates. Audiophiles may still prefer lossless formats like FLAC for the highest possible audio quality.
4. Ethical Concerns: Some critics raise ethical concerns about the licensing and patent issues related to AAC, which can be seen as a barrier to the use of open and free technologies.

Comparison between AAC File Format and Other Audio File Formats

Here's a comparison between AAC (Advanced Audio Coding) and some other popular audio formats:

Frequently Asked Questions (FAQs) around AAC Audio File Format

Q1. What is the AAC file format used for?

ANSWER - Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. Designed to be the successor of the MP3 format, AAC generally achieves higher sound quality than MP3 encoders at the same bit rate.

Q2. Is AAC a good audio format?

ANSWER- At the same bitrate, AAC offers greater sound quality than MP3. Several platforms and devices support it, including iTunes, iOS, and Android. AAC files are good for streaming because they are smaller than other lossless codecs.

Q3. What is the AAC file type format?

ANSWER- The AAC extension is short for “Advanced Audio Coding”, which is a standard audio container format for compressed digital audio and music data.

Q4. What are AAC file disadvantages?

ANSWER- One of the main disadvantages of the AAC audio file format is that it is not compatible with all media players and devices. Additionally, AAC files are generally larger in size than MP3 files, which can take up more storage space.

Q5. Is AAC higher quality than MP3?

ANSWER- The general consensus is that AAC files are, in fact, better than MP3s in terms of quality, even at the same bit rate (more on that in the conclusion). AAC's advanced compression algorithm is thought of as more “efficient” than an MP3's, and thus, of higher quality.

Q6. Is AAC better than FLAC?

ANSWER- Compared with AAC, FLAC offers better audio quality. Compared with FLAC, AAC has more devices and media players support, including Apple devices and media players, like iPhone, iPad, iPod, etc, and many non-Apple devices and media players, like Zune, PS3, Android, Blackberry, Wii, etc.

Q7. Which audio format is the best quality?

ANSWER- WAV (Waveform Audio File) retains all the original data, which makes it the ideal format for sound engineers. WAV has greater dynamic range and greater bit depth.

Q8. Is AAC a lossless format?

ANSWER- AAC is a lossy compressed format for digital audio. Advanced Audio Coding (AAC) is a standard for lossy digital audio compression originally designed as a successor to the MP3 format.

Q9. Which format has better sound quality?

ANSWER- The best audio formats for sound quality are uncompressed or lossless compression files think WAV, FLAC, and M4A. That's because these formats retain the original sound quality, though you'll have to put up with the fact these files will be large.

Q10. Which audio format is loudest?

ANSWER- The WAV offers an uncompressed format. The easiest way to envision this concept is by thinking of ocean waves. The water is loudest, fullest, and strongest when the wave is high. The same holds true for the waveform in the WAV.

Q11. Is AAC faster than MP3?

ANSWER- AAC and HE-AAC are better than MP3 at low bit rates (typically less than 128 kilobits per second). This is especially true at very low bit rates where the superior stereo coding, pure MDCT, and more optimal transform window sizes leave MP3 unable to compete.