What is an AAC file?
AAC (Advanced Audio Coding) is a standardized digital audio coding technology designed for lossy audio compression. Officially defined in the MPEG-2 Part 7 (ISO/IEC 13818-7) and later enhanced in MPEG-4 Part 3 (ISO/IEC 14496-3) standards, it was developed to succeed the older MP3 file format. A key driver for its creation was to overcome the technical limitations of MP3, which hindered the implementation of new, more efficient audio encoding and data compression methods. This advanced foundation allows the AAC format to deliver superior sound quality compared to MP3 at an identical bit rate. Due to this efficiency and quality, it has been widely adopted as the default media format by major platforms including YouTube, iPhone, iPod, iPad, and Apple iTunes. To support its broad use, a wide array of software applications and developer APIs are available to convert AAC files to other popular formats like MP3, WMA, M4A, WAV and many others.
Brief History of AAC File
AAC file format is an enhanced version of MP3 with some improvements. Contributed by several companies including the Fraunhofer Institute (Fraunhofer IIS - developers of MP3), Nokia, Dolby, AT&T and Sony, the format was declared as an international standard by Moving Picture Experts Group (MPEG) in Apr, 1997. Later in 1999, the MPEG-2 Part 7 was updated and included in the MPEG-4 family of standards. It was known as MPEG-4 Part 3, identified as ISO/IEC 14496-3: 1999 or MPEG-4 Audio.
Key Characteristics of 8SVX Files
- Full Name: Advanced Audio Coding
- File Extensions: .aac, .m4a, .mp4 (when containing audio)
- Audio Encoding: Lossy Compression
- Standardized Under: MPEG-2 Part 7 (ISO/IEC 13818-7) and MPEG-4 Part 3 (ISO/IEC 14496-3)
- Primary Goal: To be the successor to MP3, offering better sound quality at the same bitrate
- Sampling Rate: 8 Hz to 96 kHz (wider range than MP3)
AAC File Format Specifications
The AAC file format specifications allow more flexibility to design codec than MP3 does, resulting in more concurrent encoding strategies and efficient compression. The format has been choice of selection by a number of hardware platforms for its improvements over MP3 in terms of providing support for more options even at less bitrates. The AAC file format specifications are available as MPEG-2 Part 7 and MPEG-4 Part 3 (not free to download). The format uses following media types:
- audio/aac
- audio/aacp
- audio/3gpp
- audio/3gpp2
- audio/mp4
- audio/mp4a-latm
- audio/mpeg4-generic
AAC vs MP3 - Improvements
The main differences between AAC and MP3 in terms of improvements are as follow:
- AAC supports a wider range of channels (up to 48) and sampling rates (from 8 kHz to 96 kHz)
- AAC has better coding frequencies above 16 kHz
- AAC has wider limits of variation in the frequency-time resolution of a bank of filters that have lead to improved coding of transients and stationary parts of the audio signal
- More efficient and simple bank of filters: a hybrid filter bank has been replaced by the standard MDCT (modified discrete cosine transform)
- Supports enhanced effectiveness of compression usingTemporal Noise Shaping (TNS), the prediction coefficients of MDCT-time (long term prediction), parametric stereo, perceptual noise substitution, spectral band replication (SBR).
- more flexible joint stereo (different methods can be used in different frequency ranges);
Superior Sound Quality at Lower Bitrates
This is AAC’s most significant advantage. It achieves better performance through several key improvements:
- Increased Filter Banks: AAC uses a Modified Discrete Cosine Transform (MDCT) with a finer frequency resolution (1024 points vs. MP3’s 576). This allows it to represent audio signals more accurately, especially at frequencies above 16 kHz, leading to clearer and brighter sound.
- Efficient Handling of Transients: For sudden, sharp sounds (like a drum hit or clap), AAC can switch to a shorter 128-point window to minimize pre-echo artifacts, a common issue in MP3s.
FAQ
Q1: Is AAC better than MP3?
A: Yes, AAC generally provides better sound quality than MP3 at the same bitrate, making it a more efficient and advanced format.
Q2: Does AAC mean lossless audio?
A: No, AAC is a lossy compression format, meaning some audio data is discarded to reduce file size, though it does so more efficiently than MP3.
Q3: What’s the difference between .m4a and .aac files?
A: Both contain AAC audio data. An .m4a file is an MP4 container with AAC audio, while a pure .aac file typically uses the ADTS stream format without a container.
Q4: Can all devices play AAC files?
A: AAC is universally supported across all modern devices, including iPhones, Android phones, Windows, macOS, smart TVs, and gaming consoles.
Q5: Is AAC good for storing music?
A: Absolutely. AAC is an excellent format for storing music due to its high quality and efficient compression, which saves storage space without a noticeable loss in fidelity for most listeners.
