Адаптивная дифференциальная импульсно-кодовая модуляция / G7xx audio codecs
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Ориентировочная полоса пропускания в среде IP для одного разговора VoIP:
G.711 |
64 kbps |
85,6 kbps |
G.723.1 |
6,3 kbps |
20,8 kbps |
G.729 |
8 kbps |
29,6 kbps Предпочтителен ! |
G.7xx: Audio (Voice) Compression Protocols (CODEC) (G.711, G.721, G.722, G.726, G.727, G.728, G.729)
G.7xx, including G.711, G.721, G.722, G.726, G.727, G.728, G.729, is a suite of ITU-T standards for audio compression and de-commpression. It is primarily used in telephony. In telephony, there are 2 main algorithms defined in the standard, mu-law algorithm (used in America) and a-law algorithm (used in Europe and the rest of the world). Both are logarithmic, but the later a-law was specifically designed to be simpler for a computer to process. The G.7xx protocol suite compose the following protocols:
G.711 - Pulse code modulation (PCM) of voice frequencies on an 64 kbps channel. G.721 - 32 kbit/s adaptive differential pulse code modulation (ADPCM)
G.722 - 7 kHz audio-coding within 64 kbit/s
G.722.1 - Coding at 24 and 32 kbit/s for hands-free operation in systems with low frame loss
G.722.2 - Wideband coding of speech at around 16 kbit/s using adaptive multi-rate wideband (AMR-WB) G.726 - 40, 32, 24, 16 kbit/s adaptive differential pulse code modulation (ADPCM)
G.727 - 5-, 4-, 3- and 2-bit/sample embedded adaptive differential pulse code modulation (ADPCM) G.728 - Coding of speech at 16 kbit/s using low-delay code excited linear prediction
G.729 - Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP)
Protocol Structure - G.7xx: Audio (Voice) Compression Protocols (CODEC) (G.711, G.721, G.722, G.726, G.727, G.728, G.729)
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Comparison of major Audio Codec: |
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standardized |
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bit rate |
sampling |
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description |
rate |
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(kHz) |
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(ADPCM) |
Intel, IMA |
ADPCM |
32 |
8 |
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DVI |
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G.711 |
ITU-T |
Pulse code modulation (PCM) |
64 |
8 |
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G.721 |
ITU-T |
Adaptive differential pulse code modulation (ADPCM) |
32 |
8 |
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G.722 |
ITU-T |
7 kHz audio-coding within 64 kbit/s |
64 |
16 |
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G.722.1 |
ITU-T |
Coding at 24 and 32 kbit/s for hands-free operation in systems |
24/32 |
16 |
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with low frame loss |
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Extensions of Recommendation G.721 adaptive differential pulse |
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G.723 |
ITU-T |
code modulation to 24 and 40 kbit/s for digital circuit |
24/40 |
8 |
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multiplication equipment application |
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G.723.1 |
ITU-T |
Dual rate speech coder for multimedia communications |
5.6/6.3 |
8 |
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transmitting at 5.3 and 6.3 kbit/s |
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G.726 |
ITU-T |
40, 32, 24, 16 kbit/s adaptive differential pulse code modulation |
16/24/32/40 |
8 |
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(ADPCM) |
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G.727 |
ITU-T |
5-, 4-, 3- and 2-bit/sample embedded adaptive differential pulse |
var. |
? |
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code modulation (ADPCM) |
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G.728 |
ITU-T |
Coding of speech at 16 kbit/s using low-delay code excited linear |
16 |
8 |
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prediction |
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G.729 |
ITU-T |
Coding of speech at 8 kbit/s using conjugate-structure algebraic- |
8 |
8 |
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code-excited linear-prediction (CS-ACELP) |
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GSM |
ETSI |
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Regular Pulse Excitation Long Term Predictor (RPE-LTP) |
13 |
8 |
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06.10 |
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Related Protocols |
: RTSP , RTP , RTCP , H.323 , H.245 , H.263 |
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Sponsor Source |
: G.7xx is a suite of ITU-T (http://www.itu.int/ITU-T/ ) standard. |
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