G.729.1

{{short description|ITU-T Recommendation}}

{{Infobox technology standard

| title = G.729.1

| long_name = G.729-based embedded variable bit-rate coder: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729

| image = Pcm.svg

| caption =

| status = In force

| year_started = 2006

| version = (03/13)

| version_date = March 2013

| preview =

| preview_date =

| organization = ITU-T

| committee = ITU-T Study Group 16

| base_standards =

| related_standards = G.711, G.729

| abbreviation =

| domain = audio compression

| license = Non-free

| website = https://www.itu.int/rec/T-REC-G.729.1

}}

G.729.1 is an 8-32 kbit/s embedded speech and audio codec providing bitstream interoperability with G.729, G.729 Annex A and G.729 Annex B.{{Cite web|title=G.729.1: G.729-based embedded variable bit-rate coder: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729|url=https://www.itu.int/rec/T-REC-G.729.1|url-status=live|archive-url=https://web.archive.org/web/20210406195038/https://www.itu.int/rec/T-REC-G.729.1|archive-date=2021-04-06|access-date=2021-04-06|website=www.itu.int}} Its official name is G.729-based embedded variable bit rate codec: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729. It was introduced in 2006.{{cite book |last1=Nagireddi |first1=Sivannarayana |title=VoIP Voice and Fax Signal Processing |date=2008 |publisher=John Wiley & Sons |isbn=9780470377864 |page=69 |url=https://books.google.com/books?id=5AneeZFE71MC&pg=PA69}}

This codec has been designed to provide better quality and more flexibility than the existing ITU-T G.729 speech coding standard.

G.729.1 is scalable in bit rate, acoustic bandwidth and complexity.

In addition it offers various encoder and decoder modes, including the support of both 8 and 16 kHz input/output sampling frequency, compatibility with G.729B, and reduced algorithmic delay.

The bitstream of G.729.1 is structured into 12 hierarchical layers.

The first layer (or core layer) at 8 kbit/s follows the G.729 format.

The second layer (adds 4 kbit/s for a total of 12 kbit/s) is a narrowband enhancement layer. The third layer (2 kbit/s for a total of 14 kbit/s) is a bandwidth extension layer. Further layers (in 2 kbit/s steps) are wideband enhancement layers.

The G.729.1 output bandwidth is 50–4000 Hz at 8 and

12 kbit/s, and 50–7000 Hz from 14 to 32 kbit/s. G.729.1 is also known as G.729 Annex J and G.729EV where EV stands for Embedded Variable (bit rate).

The G.729.1 algorithm is based on a three-stage coding structure: embedded code-excited linear prediction (CELP) coding of the lower band (50–4000 Hz), parametric coding of the higher band (4000–7000 Hz) by Time-Domain Bandwidth Extension (TDBWE), and enhancement of the full band (50–7000 Hz) by a predictive transform coding technique referred to as time-domain aliasing cancellation (TDAC) or modified discrete cosine transform (MDCT) coding.