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nt0 x\;X&E4B2~b,X0G.7xx: Audio (Voice) Compression Protocols (CODEC) (G.711, G.721, G.722, G.726, G.727, G.728, G.729)51Testing软件测试网5K"r9|+B'l
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QKIfG.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:51Testing软件测试网 `:` nI%uR!om
!O.Q&bN7\%r{+\0G.711 - Pulse code modulation (PCM) of voice frequencies on an 64 kbps channel.51Testing软件测试网(Eq/aL ~n t
t+|T7f;y9TK7W _0G.721 - 32 kbit/s adaptive differential pulse code modulation (ADPCM)
"uqD)W/y F0G.722 - 7 kHz audio-coding within 64 kbit/s
2u0l2^ E VF5t0G.722.1 - Coding at 24 and 32 kbit/s for hands-free operation in systems with low frame loss51Testing软件测试网 j iM_Y
G.722.2 - Wideband coding of speech at around 16 kbit/s using adaptive multi-rate wideband (AMR-WB)51Testing软件测试网4j!y#L2M/I
G.726 - 40, 32, 24, 16 kbit/s adaptive differential pulse code modulation (ADPCM)
h#g6x Wz0p0G.727 - 5-, 4-, 3- and 2-bit/sample embedded adaptive differential pulse code modulation (ADPCM)51Testing软件测试网{o9YB
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G.728 - Coding of speech at 16 kbit/s using low-delay code excited linear prediction51Testing软件测试网 V:yHVp w}$LD c
G.729 - Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP)51Testing软件测试网`4b%BP2x7z)t9q3l
O&y*Sd5j9k0针对音频压缩不同标准组织和公司有很多不同技术和标准可用，在下列表格中，主要的被列举如下：
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Oq"rGa051Testing软件测试网AdVT/f*V CSName | Standardized by | Modulate | Bit rate (kb/s) | Sample rate (kHz) | Frame size (ms) | 压缩延迟 | 平均主观评分(MOS) | Remarks |
(ADPCM) DVI | | ADPCM | 32 | 8 | Sample | | | |
G.711 | | PCM | 64 | 8 | Sample (0.125) | 0.75 | 4.1 | mu-law (US, Japan) and A-law (Europe) |
| G.721 | ITU-T | ADPCM | 32 | 8 | Sample | | | 被G.726替代 |
| G.722 | ITU-T | ADPCM | 64 | 16 | Sample | | | 分波段编解码器，其将16 kHz波段分为两个分波段，每个编码使用 ADPCM |
G.722.1 | | 基于交换的 | 24/32 | 16 | 20 | 40 | | |
| G.722.2 | ITU-T | AMR-WB (Adaptive Multi-Rate Wideband) | 6.60, 8.85, 12.65, 14.25, 15.85, 18.25, 19.85, 23.05, 23.85 | | Sample | | | AMR-WB 是在网络中使用而标准化的，例如UMTS。 |
| G.723 | ITU-T | DPCM | 24/40 | 8 | Sample | 30 | | 被G.726替代了，它相对G.723.1是完全不同的编解码器。 |
G.723.1 | | MPC-MLQ 或ACELP
9Bk"f*hT9] ~;U9b0Dual rate, 5.3 and 6.3 kbit/s | 5.6/6.3 | 8 | 30 | 30 | 3.7~3.9 | For the high rate coder is MP-MLQ and for the low rate coder is ACELP. H.324视频会议的一部分 |
G.726 | | 40, 32, 24, 16 kbit/s ADPCM | 16/24/32/40 | 8 | sample (0.125) | 1 | 3.9 | 被G.721和 G.723替代? |
| G.727 | ITU-T | ADPCM | 5-, 4-, 3- and 2 | | 采样 | | | 与G.726相关 |
| G.728 | ITU-T | LDCELP | 16 | 8 | 0.625 | 0.625 | 3.6 | |
G.729 | | CS-ACELP | 8 | 8 | 10 | 15 | 3.9 | Low delay (15 ms). VOIP应用程序 |
| GSM 06.10 | ETSI | RPE-LTP | 13 | 8 | 22.5 | | | 用在GSM蜂窝电话上。 |
| LPC10 | USA Government DOD / NATO | LPC | 2.4 | 8 | 22.5 | | | 也叫做FS-1015或STANAG 4198 |
| Speex | 自由软件 | CELP | 8, 16, 32 | 2.15-24.6 (NB)
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34 ( WB ) | 30 – 34 | | VOIP |
| iLBC(因特网低比特率声音合成器) | IETF RFC 3951自由软件 | LPC | 8, 16 | 13.3 | 30 | 30 | 4 | VOIP |
| LPC | 8, 16 | 15.2 | 20 | 20 | 4 |
| DoD CELP | 美国国防部门 | CELP | 4.8 | | 30 | | | |
| EVRC | 3GPP2 | 增强型可变率编解码器 | 9.6/4.8/1.2 | 8 | 20 | | | 用在CDMA网络上。 |
| L16 | IETF RFC 3551 | 非压缩音频数据压缩 | 128 | 变量 | 采样 | | | |
9@`.S7tr8LB@*F0 R p%{mn[i)l0Reference:51Testing软件测试网&L ]%t
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51Testing软件测试网0l1E }+YBhttp://www.networkdictionary.cn/Software/Audio-Compression-and-Codec.php51Testing软件测试网6]5];\ ?.?#b"A
http://www.javvin.com/protocolG7xx.html51Testing软件测试网/z"Hm*jqM;l U
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