science

G.722

G.722 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 G.722 rather than just read about it. In short: G.722 is an ITU-T standard 7 kHz wideband audio codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988.

Key takeaways

G.722 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect G.722 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of G.722 from memory before moving on to harder problems.

Reference excerpt

G.722 is an ITU-T standard 7 kHz wideband audio codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988. Technology of the codec is based on sub-band ADPCM (SB-ADPCM). The corresponding narrow-band codec based on the same technology is G.726. G.722 provides improved speech quality due to a wider speech bandwidth of 50–7000 Hz compared to narrowband speech coders like G.711 which in general are optimized for POTS wireline quality of 300–3400 Hz. G.722 sample audio data at a rate of 16 kHz (using 14 bits), double that of traditional telephony interfaces, which results in superior audio quality and clarity. Other ITU-T 7 kHz wideband codecs include G.722.1 and G.722.2. These codecs are not variants of G.722 and they use different patented compression technologies. G.722.1 is based on Siren codecs and offers lower bit-rate compressions (24 kbit/s or 32 kbit/s). It uses a modified discrete cosine transform (MDCT) audio coding data compression algorithm. A more recent G.722.2, also known as AMR-WB ("Adaptive Multirate Wideband") is based on ACELP and offers even lower bit-rate compressions (6.6 kbit/s to 23.85 kbit/s), as well as the ability to quickly adapt to varying compressions as the network topography mutates. In the latter case, bandwidth is automatically conserved when network congestion is high. When congestion returns to a normal level, a lower-compression, higher-quality bitrate is restored.

Applications G.722 is an ITU standard codec that provides 7 kHz wideband audio at data rates from 48, 56 and 64 kbit/s. This is useful for voice over IP applications, such as on a local area network where network bandwidth is readily available, and offers a significant improvement in speech quality over older narrowband codecs such as G.711, without an excessive increase in implementation complexity. Environments where bandwidth is more constrained may prefer one of the more bitrate-efficient codecs, such as G.722.1 (Siren7) or G.722.2 (AMR-WB). G.722 has also been widely used by radio broadcasters for sending commentary-grade audio over a single 56 or 64 kbit/s ISDN B-channel (the least significant bit is dropped on 56 kb circuits). G.722 works by having the inbound voice signal pass through a digital filter that splits the audio signal into 0 Hz-to-4 kHz and 4 kHz-to-8 kHz audio bands. These sub-bands are then encoded using sub-band ADPCM. Most of the human voice energy is concentrated in the lower half of the audio band (0–4 kHz), so 48 kbit/s of the bandwidth is dedicated to the lower sub-band and the other 16 kbit/s is allocated to the higher sub-band.

RTP encapsulation G.722 VoIP is typically carried in RTP payload type 9. Note that IANA records the clock rate for type 9 G.722 as 8 kHz (instead of 16 kHz), RFC 3551 clarifies that this is due to a historical error and is retained in order to maintain backward compatibility. Consequently, correct implementations represent the value 8,000 where required but encode and decode audio at 16 kHz. Whilst G.722 allows for bitrates of 64, 56 and 48 kbit/s, in practice, data is encoded at 64 kbit/s, with bits from the lower sub-band being used to encode auxiliary data. The greater the number of bits allocated to aux data, the lower the bit rate.

Licensing G.722 patents have expired, so it is freely available.

See also List of codecs Comparison of audio coding formats Wideband audio

References

External links ITU-T Recommendation G.722: 7 kHz audio-coding within 64 kbit/s- technical specification

Illustrations

Worked examples

Example 1 — a first encounter with G.722

Start with the simplest possible case. Write down what G.722 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 G.722 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 G.722 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 G.722

In research: G.722 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 G.722 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: G.722 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audio codecs, ITU-T G Series Recommendations, ITU-T recommendations, so understanding it makes those chapters shorter.
In everyday life: Look for G.722 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 G.722 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what G.722 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 G.722 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is G.722 in simple terms?

G.722 is an ITU-T standard 7 kHz wideband audio codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988.

Why does G.722 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 G.722?

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 G.722.