science

High-Efficiency Advanced Audio Coding

High-Efficiency Advanced Audio Coding is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand High-Efficiency Advanced Audio Coding rather than just read about it. In short: High-Efficiency Advanced Audio Coding (HE-AAC) is an audio coding format for lossy data compression of digital audio as part of the MPEG-4 standards. It is an extension of Low Complexity AAC (AAC-LC) optimized for low-bitrate applications such as streaming audio.

Key takeaways

High-Efficiency Advanced Audio Coding belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect High-Efficiency Advanced Audio Coding to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of High-Efficiency Advanced Audio Coding from memory before moving on to harder problems.

Reference excerpt

High-Efficiency Advanced Audio Coding (HE-AAC) is an audio coding format for lossy data compression of digital audio as part of the MPEG-4 standards. It is an extension of Low Complexity AAC (AAC-LC) optimized for low-bitrate applications such as streaming audio. The usage profile HE-AAC v1 uses spectral band replication (SBR) to enhance the modified discrete cosine transform (MDCT) compression efficiency in the frequency domain. The usage profile HE-AAC v2 couples SBR with Parametric Stereo (PS) to further enhance the compression efficiency of stereo signals. HE-AAC is defined as an MPEG-4 Audio profile in ISO/IEC 14496–3. HE-AAC is used in digital radio standards like HD Radio, DAB+ and Digital Radio Mondiale.

History The progenitor of HE-AAC was developed by Coding Technologies by combining MPEG-2 AAC-LC with a proprietary mechanism for spectral band replication (SBR), to be used by XM Radio for their satellite radio service. Subsequently, Coding Technologies submitted their SBR mechanism to MPEG as a basis of what ultimately became HE-AAC. HE-AAC v1 was standardized as a profile of MPEG-4 Audio in 2003 by MPEG and published as part of the ISO/IEC 14496-3:2001/Amd 1:2003 specification. The HE-AAC v2 profile was standardized in 2006 as per ISO/IEC 14496-3:2005/Amd 2:2006. Parts of the HE-AAC specification had previously been standardized and published by various bodies in 3GPP TS 26.401 , ETSI TS 126 401 V6.1.0 , ISO/IEC 14496-3:2001/Amd.1:2003 and ISO/IEC 14496-3:2001/Amd 2:2004.

At the time, Coding Technologies had already begun using the trade names AAC+ and aacPlus for what is now known as HE-AAC v1, and aacPlus v2 and eAAC+ for what is now known as HE-AAC v2.

Perceived quality Testing indicates that material decoded from 64 kbit/s HE-AAC does not quite have similar audio quality to material decoded from MP3 at 128 kbit/s using high quality encoders. The test, taking bitrate distribution and RMSD into account, is a tie between mp3PRO, HE-AAC and Ogg Vorbis. Further controlled testing by 3GPP during their revision 6 specification process indicates that HE-AAC and HE-AAC v2 provide "Good" audio quality for music at low bit rates (e.g., 24 kbit/s). In 2011, a public listening test comparing the two best-rated HE-AAC encoders at the time to Opus and Ogg Vorbis indicated that Opus had statistically significant superiority at 64 kbit/s over all other contenders. Apple's implementation of HE-AAC was ranked second. Ogg Vorbis and Nero HE-AAC tied for third place. MPEG-2 and MPEG-4 AAC-LC decoders without SBR support will decode the AAC-LC part of the audio, resulting in audio output with only half the sampling frequency, thereby reducing the audio bandwidth. This usually results in the high-end, or treble, portion of the audio signal missing from the audio product.

Support

Encoding Orban Opticodec-PC Streaming and File Encoders were the first commercially available encoders supporting AAC-LC/HE-AAC back in 2003. They are now deprecated and replaced with StreamS Encoders from StreamS/Modulation Index with many more features, including support xHE-AAC/Unified Speech and Audio Coding. They are now in use at some of the largest content providers, and are considered to be the standard of the industry for live encoding. Sony supports HE-AAC encoding since SonicStage version 4. iTunes 9 supports HE-AAC encoding and playback. Nero has released a free-of-charge command line HE-AAC encoder, Nero AAC Codec, and also supports HE-AAC inside the Nero software suite. Sorenson Media's Squeeze Compression Suite includes an HE-AACv1 encoder and is available for macOS as well as Windows. The 3GPP consortium released source code of a reference HE-AACv2 encoder that appears to offer competitive quality. Winamp Pro also supports ripping music to HE-AAC. Using a transcoding plugin for Winamp's media library, any file can be transcoded to HE-AAC. XLD, a macOS audio encoding program, offers encoding from any of its supported formats to HE-AAC. Nokia PC Suite may encode audiofiles to eAAC+ format before transmitting them to mobile phone. HE-AAC v1 and v2 encoders are provided by the Fraunhofer FDK AAC library in Android 4.1 and later versions.

Decoding HE-AAC is supported in the open source FAAD/FAAD2 decoding library and all players incorporating it, such as VLC media player, Winamp, foobar2000, Audacious Media Player and SonicStage. The Nero AAC Codec supports decoding HE and HEv2 AAC. HE-AAC is also used by AOL Radio and Pandora Radio clients to deliver high-fidelity music at low bitrates. iTunes 9.2 and iOS 4 include full decoding of HE-AAC v2 parametric stereo streams.

iTunes 9 thru 9.1, iPhone OS 3.1 and Fall 2009 iPods have support for HE-AAC playback for version 1 with no parametric stereo. Older versions of Apple iTunes, iPod Touch, and iPhone will play HE-AAC files at reduced fidelity because they ignore the spectral-band replication and parametric stereo information, instead playing them as though they were standard AAC-LC files without the high-frequency, or "treble," information that is only present in the SBR part of the signal. These will report the track length as twice its actual length. Dolby released Dolby Pulse decoders and encoders in September 2008. HE-AAC v2 is the core of Dolby Pulse so files and streams encoded in Dolby Pulse will playback on AAC, HE-AAC v1 and v2 decoders. Conversely files and streams encoded in AAC, HE-AAC v1 or v2 will playback on Dolby Pulse decoders. Dolby Pulse provides the following additional capabilities beyond HE-AAC v2:

Ability to intelligently generate and insert reversible loudness normalization and dynamic range metadata into the encoded file/stream; this metadata can then be used to optimize the playback experience based on application and/or device. Ability to insert custom metadata into the encoded file, and extract this metadata on playback Dolby has additionally released a PC decoder as an SDK suitable for integration into PC applications requiring Dolby Pulse, HE-AAC or AAC playback capabilities. HE-AAC v2 decoders are provided in all versions of Android. Decoding is handled by Fraunhofer FDK AAC since Android version 4.1.

Clients

Promotion aspects

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Illustrations

Hierarchical structure of AAC profile, HE-AAC profile and HE-AAC v2 profile, and compatibility between them. The HE-AAC profile decoder is fully capable of decoding any AAC profile stream. Similarly, The HE-AAC v2 decoder can handle all HE-AAC profile streams as well as all AAC profile streams. Based on the MPEG-4 Part 3 technical specification.[1]

Evolution from MPEG-2 AAC-LC (Low Complexity) Profile and MPEG-4 AAC-LC Object Type to HE-AAC v2 Profile[2]

Worked examples

Example 1 — a first encounter with High-Efficiency Advanced Audio Coding

Start with the simplest possible case. Write down what High-Efficiency Advanced Audio Coding claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to High-Efficiency Advanced Audio Coding before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about High-Efficiency Advanced Audio Coding ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of High-Efficiency Advanced Audio Coding

In research: High-Efficiency Advanced Audio Coding appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses High-Efficiency Advanced Audio Coding in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: High-Efficiency Advanced Audio Coding is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audio codecs, IEC standards, ISO standards, so understanding it makes those chapters shorter.
In everyday life: Look for High-Efficiency Advanced Audio Coding outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study High-Efficiency Advanced Audio Coding in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what High-Efficiency Advanced Audio Coding means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain High-Efficiency Advanced Audio Coding out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is High-Efficiency Advanced Audio Coding in simple terms?

Why does High-Efficiency Advanced Audio Coding matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study High-Efficiency Advanced Audio Coding?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on High-Efficiency Advanced Audio Coding.