音频压缩和编解码（Audio (Voice) Compression and Codec）
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51Testing软件测试网+}\%w;Uh5A AG.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+P]:B"n!W-{0i
r.uO"K9B sO e \SG0G.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:
P"{!I]x0U j9T{ U0G.711 - Pulse code modulation (PCM) of voice frequencies on an 64 kbps channel.51Testing软件测试网&mx M R8Bd*Ld
51Testing软件测试网[C5z\SG.721 - 32 kbit/s adaptive differential pulse code modulation (ADPCM)51Testing软件测试网i-T4sf wU
G.722 - 7 kHz audio-coding within 64 kbit/s
0Xs;p.P!P3C!I0G.722.1 - Coding at 24 and 32 kbit/s for hands-free operation in systems with low frame loss51Testing软件测试网L.e;i:s'G1[7w Qm
G.722.2 - Wideband coding of speech at around 16 kbit/s using adaptive multi-rate wideband (AMR-WB)
3`N A%~3Et!y]0G.726 - 40, 32, 24, 16 kbit/s adaptive differential pulse code modulation (ADPCM)
H6p]%dmE)H0G.727 - 5-, 4-, 3- and 2-bit/sample embedded adaptive differential pulse code modulation (ADPCM)
_0c Z8Z*n;@l)B0G.728 - Coding of speech at 16 kbit/s using low-delay code excited linear prediction
:o^*o7n N&a0G.729 - Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP)
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yu^051Testing软件测试网({@$~/l(aQ8[`8}针对音频压缩不同标准组织和公司有很多不同技术和标准可用，在下列表格中，主要的被列举如下：
#{e a KVck051Testing软件测试网 g+X6P4Z8F-\,W#NName | Standardized by | Modulate | Bit rate (kb/s) | Sample rate (kHz) | Frame size (ms) | 压缩延迟 | 平均主观评分(MOS) | Remarks |
(ADPCM) DVI | | ADPCM | 32 | 8 | Sample | | | |
G.711 | | PCM | 64 | 8 | Sample (0.125) | 0.75 | 4.1 | mu-law (US, Japan) and A-law (Europe) |
| G.721 | ITU-T | ADPCM | 32 | 8 | Sample | | | 被G.726替代 |
| G.722 | ITU-T | ADPCM | 64 | 16 | Sample | | | 分波段编解码器，其将16 kHz波段分为两个分波段，每个编码使用 ADPCM |
G.722.1 | | 基于交换的 | 24/32 | 16 | 20 | 40 | | |
| G.722.2 | ITU-T | AMR-WB (Adaptive Multi-Rate Wideband) | 6.60, 8.85, 12.65, 14.25, 15.85, 18.25, 19.85, 23.05, 23.85 | | Sample | | | AMR-WB 是在网络中使用而标准化的，例如UMTS。 |
| G.723 | ITU-T | DPCM | 24/40 | 8 | Sample | 30 | | 被G.726替代了，它相对G.723.1是完全不同的编解码器。 |
G.723.1 | | MPC-MLQ 或ACELP51Testing软件测试网 r@9h r s p8t!x|
Dual rate, 5.3 and 6.3 kbit/s | 5.6/6.3 | 8 | 30 | 30 | 3.7~3.9 | For the high rate coder is MP-MLQ and for the low rate coder is ACELP. H.324视频会议的一部分 |
G.726 | | 40, 32, 24, 16 kbit/s ADPCM | 16/24/32/40 | 8 | sample (0.125) | 1 | 3.9 | 被G.721和 G.723替代? |
| G.727 | ITU-T | ADPCM | 5-, 4-, 3- and 2 | | 采样 | | | 与G.726相关 |
| G.728 | ITU-T | LDCELP | 16 | 8 | 0.625 | 0.625 | 3.6 | |
G.729 | | CS-ACELP | 8 | 8 | 10 | 15 | 3.9 | Low delay (15 ms). VOIP应用程序 |
| GSM 06.10 | ETSI | RPE-LTP | 13 | 8 | 22.5 | | | 用在GSM蜂窝电话上。 |
| LPC10 | USA Government DOD / NATO | LPC | 2.4 | 8 | 22.5 | | | 也叫做FS-1015或STANAG 4198 |
| Speex | 自由软件 | CELP | 8, 16, 32 | 2.15-24.6 (NB)
ZY,P9T |*I*v6ey#v04-44.2 (WB) | 30 ( NB )51Testing软件测试网3|+y/L'm M5I&z#VJR!J
34 ( WB ) | 30 – 34 | | VOIP |
| iLBC(因特网低比特率声音合成器) | IETF RFC 3951自由软件 | LPC | 8, 16 | 13.3 | 30 | 30 | 4 | VOIP |
| LPC | 8, 16 | 15.2 | 20 | 20 | 4 |
| DoD CELP | 美国国防部门 | CELP | 4.8 | | 30 | | | |
| EVRC | 3GPP2 | 增强型可变率编解码器 | 9.6/4.8/1.2 | 8 | 20 | | | 用在CDMA网络上。 |
| L16 | IETF RFC 3551 | 非压缩音频数据压缩 | 128 | 变量 | 采样 | | | |
9N YC:D#g/xoG07MzxxA*` yt5u0Reference:
FOo| G*z q)Q0:F$LJP rQ0http://www.networkdictionary.cn/Software/Audio-Compression-and-Codec.php51Testing软件测试网Y)hC9B2IB1R
http://www.javvin.com/protocolG7xx.html
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