science

Unified Speech and Audio Coding

Unified Speech and 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 Unified Speech and Audio Coding rather than just read about it. In short: Unified Speech and Audio Coding (USAC) is an audio compression format and codec for both music and speech or any mix of speech and audio using very low bit rates between 12 and 64 kbit/s. It was developed by Moving Picture Experts Group (MPEG) and was published as an international standard ISO/IEC 23003-3 (a.k.a.

Key takeaways

Unified Speech and 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 Unified Speech and Audio Coding to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Unified Speech and Audio Coding from memory before moving on to harder problems.

Reference excerpt

Unified Speech and Audio Coding (USAC) is an audio compression format and codec for both music and speech or any mix of speech and audio using very low bit rates between 12 and 64 kbit/s. It was developed by Moving Picture Experts Group (MPEG) and was published as an international standard ISO/IEC 23003-3 (a.k.a. MPEG-D Part 3) and also as an MPEG-4 Audio Object Type in ISO/IEC 14496-3:2009/Amd 3 in 2012. It uses time-domain linear prediction and residual coding tools (ACELP-like techniques) for speech signal segments and transform coding tools (MDCT-based techniques) for music signal segments and it is able to switch between the tool sets dynamically in a signal-responsive manner. It is being developed with the aim of a single, unified coder with performance that equals or surpasses that of dedicated speech coders and dedicated music coders over a broad range of bitrates. Enhanced variations of the MPEG-4 Spectral Band Replication (SBR) and MPEG-D MPEG Surround parametric coding tools are integrated into the USAC codec.

Extended HE-AAC The MPEG-D USAC standard (ISO/IEC 23003-3) defines the Extended High Efficiency AAC profile, which contains all of the tools of the HE-AAC v2 profile plus the mono/stereo capabilities of the Baseline USAC profile. As a result, a decoder built according to the Extended High Efficiency AAC profile is able to also decode the bit streams created for the previous AAC family profiles. The Extended High Efficiency AAC profile was designed for applications relying on a consistent performance at low data rates while being able to decode all existing AAC-LC, HE-AAC and HE-AACv2 content.

xHE-AAC

Fraunhofer has defined the xHE-AAC codec as the combination of the Extended High Efficiency AAC profile and appropriate parts of the MPEG-D DRC Loudness Control Profile or Dynamic Range Control Profile. xHE-AAC extends the operating range of the codec from 12 to 300 kbit/s for stereo signals and allows seamless switching between bitrates over this range for adaptive bitrate delivery (using standards such as MPEG-DASH or HLS for example). xHE-AAC also includes MPEG-D DRC mandatory loudness control to playback content at a consistent volume and offers new dynamic range control profiles for listening in noisy situations. While xHE-AAC decoders will be able to decode the bit streams created for the previous AAC family profiles, xHE-AAC encoders are typically intended for encoding of MPEG-D USAC audio object type (AOT 42) with MPEG-D DRC loudness metadata, though some may support encoding legacy AAC object types. xHE-AAC is a mandatory audio codec in the Digital Radio Mondiale standard and is a trademark of Fraunhofer. In April 2016, Via Licensing announced the launch of a xHE-AAC patent pool licensing program for 2016. In 2018, xHE-AAC was included in Via Licensing's AAC patent pool at no additional cost. In January 2021, Fraunhofer announced a test service and trademark program for xHE-AAC and announced that the codec is being used by Netflix. Netflix reported that users switched from speakers to headphones 16% less often (due to poor sound quality or inadequate volume) on high dynamic range content when using xHE-AAC instead of HE-AAC. Netflix also explained that xHE-AAC allowed them to begin streaming with adaptive audio bitrates to Android devices. Fraunhofer also announced xHE-AAC licenses to MainConcept, Poikosoft, and LG. xHE-AAC is supported by the Bento4 DASH/HLS packager. In January 2022, MainConcept established a web encoding service to test xHE-AAC. In October 2022, xHE-AAC decoding was added to Windows 11 and Xbox devices.

Compatibility xHE-AAC is supported in Android since Android Pie and in iOS since iOS 13. It has been announced that it will be added to watchOS 7 and has been licensed to Microsoft. Playing xHE-AAC audio files is supported in foobar2000 from version 2.25 onwards. In October 2022, Windows 11 added support for xHE-AAC in the 22H2 update.

See also Opus (codec) – a royalty free alternative, low latency codec for a similar usage

References

External links Fraunhofer xHE-AAC Website Fraunhofer AAC Audio Playback Test Site xHE-AAC encoder for Windows 7/8/10/11 Fraunhofer xHE-AAC Trademark Program Fraunhofer xHE-AAC Codec Test Service Netflix Tech Blog: Optimizing the Aural Experience on Android Devices with xHE-AAC

Worked examples

Example 1 — a first encounter with Unified Speech and Audio Coding

Start with the simplest possible case. Write down what Unified Speech and 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 Unified Speech and 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 Unified Speech and 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 Unified Speech and Audio Coding

In research: Unified Speech and 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 Unified Speech and 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: Unified Speech and Audio Coding is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audio codecs, MPEG, Open standards covered by patents, so understanding it makes those chapters shorter.
In everyday life: Look for Unified Speech and 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 Unified Speech and Audio Coding in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Unified Speech and 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 Unified Speech and Audio Coding out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Unified Speech and Audio Coding in simple terms?

Why does Unified Speech and 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 Unified Speech and 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 Unified Speech and Audio Coding.