ITU-TG.723.1语音编码算法的分析及优化

G.723.1是国际电信联盟（ITU）于1996年推出的低码率语音编码标准,针对ITU-T G.723.1语言编码算法中的两个关键模块进行了分析和优化以减小算法复杂度和节约内存空间,使得算法有可能在DSP上实时实现。     

基于DSP的音频信号压缩通信系统的设计与实现

针对数据采集系统中语音传输受传输距离、成本等方面限制的问题,设计了一种低成本的语音信号压缩实时通信系统。采用模块化的方法进行硬件设计,通过将精简的TCP/IP协议移植到以太网控制芯片中来实现局域网通信,在DSP上优化实现了G.723.1语音编码算法,编码后的语音数据通过socket传送到PC端,PC端接收解码并实时播放。实验结果表明在语音质量略有退化的情况下,算法复杂度降低了,系统实现了语音信号远距离的实时传输。     

G.723.1语音编解码的DSP实时实现

本文介绍了 G.723.1语音编解码算法及 LSI Logic 公司推出的一种基于 ZSP400内核的定点 DSP(LSI402ZX)，设计了一个用于可视电话的语音编解码子系统，并描述了 G.723.1算法在 LSI402ZX 上的实时实现方法，从而实现了实时语音传输的功能。     

一种基于CK嵌入式CPU的G.729A语音编解码器

参考传统的语音压缩编码器的实现方法,提出一种基于CK嵌入式CPU的G.729A语音编解码器.介绍了G.729A语音算法的基本原理,并详细讨论了G.729A算法在国产嵌入式CPU CK510E上实时实现的算法和代码优化方法,实验结果证明优化后算法性能得到了很大地提高,平均编解码一帧语音数据时间小于10 ms,满足实际应用的要求.这些优化的思想也适用于G.729A算法在其他类似CPU平台上的实现.     

G.718宽带语音编解码器的DSP实现及优化

G.718是ITU-T最新提出的一种嵌入式可变速率宽带语音和音频编解码标准,该算法将语音信号进行分类编码,算法复杂度大大增加,但可以在窄带和宽带均达到极佳的语音质量.在分析其算法原理和关键技术的基础上,结合TMS320C55x系列DSP平台和G.718算法特点,提出了合理的汇编优化实现方案,在TMS320C5505EVM上完成了实时宽带语音编解码器.实验测试表明,G.718算法的语音质量优于同类型其他算法的宽带语音编解码器.     

G.723.1编译码算法的DSP实现

介绍了ITU－T G.723.1标准语音编译码器的算法及其在ADSP－2181芯片上的实现，软硬件结合实现了语音信号的采样和实时编译码，安全符合ITU－T G.723.1标准的定点算法，通过了ITU－T的所有测试向量。     

基于VC5409的双速率语音编译码器的实现

ITU-T.G.723.1为国际电信联盟(ITU)制定的5·3bit/s和6.3kbit/s双速率语音编码建议,分别采用代数码激励线性预测(ACELP)算法和多脉冲最大似然量化(MP-MLQ)算法。在阐述G.723.1建议编译码算法的原理和实现的基础上,重点介绍了在开发基于TMS320VC5409实时实现该建议的全双工编译器过程中所做的工作。该语音编译码器通过了G.723.1所有测试矢量的验证。     

一种G.729ab和G.723.1联合多通道声码器设计

以TMS320C6203为硬件平台,设计了一种高效率的G.729ab和G.723.1联合多通道声码器.该声码器的不同通道可同时实现G.729ab和G.723.1两种语音压缩算法.通过使用纯汇编指令与C语言结合优化编程,提高核心编解码算法效率,可实时最大支持31个话路语音的G.729ab编解码,或22个话路语音的G.723.1编解码.利用TMS320C6203在片外设McBSP提供声码器连接PSFN的标准E1接口;利用TMS320C6203的HPI接口提供声码器和连接数据网的RTP协议接口,使该联合声码器可灵活应用于媒体网关.     

基于DSP的多功能数字语音记录系统

介绍了一种基于ADSP_2181并应用ITU-T的G.723.1标准进行语音编解码的多功能数字语音系统。首先给出系统硬件框图，对各模块功能进行了阐述；还介绍了IUP-T的G.723.1标准算法原理；重点论述了控制及接口的软件设计思想，并给出主程序流程图。实现语音信息的采集与播放，主观测评合成语音达到通信质量。     

基于TMS320VC5416的G.723.1语音编码算法的实现

G．723．1标准是一种针对语音的极低码率编解码算法，该标准提供了6．3kb／s和5．3kb／s两种码率的编码算法，两种码率都能提供较好的语音质量。本文从G．723．1编码算法和解码算法2方面介绍了G．723．1极低码率编解码器算法，并从硬件实现方面对TMS320VC5416的性能参数和技术指标进行了简要的介绍，最后从实时语音信号采集、实时语音编码模块、实时语音解码模块、语音输出模块等几个方面描述了G．723．1编解码算法在TMS320VC5416上的实现过程。研究结果表明。在TMS320VC5416DSK可以实现对语音信号的实时编解码。     

U.H.F. low-noise GaAs m.e.s.f.e.t. amplifier for colour t.v. broadcasting translator

Low-noise amplifiers for u.h.f. colour t.v. broadcasting translator use have been successfully developed by using 1 ?m gate GaAs m.e.s.f.e.t.s. The obtained performances revealed that a GaAs m.e.s.f.e.t. has low-noise and low intermodulation distortion characteristics, even in the 500?800 MHz frequency range, compared with a Si bipolar transistor.     

Current-kink noise of n-channel enhancement e.s.f.i.-m.o.s. s.o.s. transistors

An experimental study of the low-frequency-noise properties of n-channel epitaxial silicon films on insulator m.o.s. s.o.s. transistors has been performed. The measurements show an excessive noise contribution at drain voltages corresponding to the current-kink effect for temperatures ranging from 4.2 to 300 K.     

Switching in m.i.s.m. and m.i.s.i.m. structures

Switching has been observed in metal?thin-insulator?n-p+ structures, where the thin insulator is SiO2, or polycrystalline silicon. In this letter two alternative structures are discussed in which the n-p+ junction is replaced by a Schottky barrier. In the second device proposed two thin-insulator structures back-to-back are shown to exhibit bidirectional switching.     

Noise behaviour of the m.o.s.f.e.t. at v.h.f. and u.h.f.

The optimum noise figures of an m.o.s.f.e.t. at u.h.f. and at pinch-off are calculated using a simplified equivalent circuit. The noise parameters are also determined experimentally. Theory and experiment are shown to be in good agreement. Noise parameters of the m.o.s.f.e.t. for the frequency range 0.1?0.8 GHz are given.     

Power m.o.s.f.e.t. linear h.f. amplifiers

N-channel silicon m.o.s. transistors for h.f. power applications have been fabricated which are optimised for linear amplification. These devices exhibit 2 W output power and 11 dB power gain at 630 MHz in class-A operation. The intercept point for third-order intermodulation distortion is 48dBm, which is considerably more than the same data obtainable with bipolar transistors.     

Wide-range monolithic bipolar?j.f.e.t. c.c.o.

A new monolithic current-controlled oscillator (c.c.o.) has been realised in a j.f.e.t.-bipolar technology. Its main advantages are a highly-linear seven decade frequency range and easy temperature compensation for frequency and output voltage.     

GaAs m.a.o.s.f.e.t. memory transistor

A new non-volatile memory device is reported. This device is a GaAs m.o.s.f.e.t. with charge storage in the gate in which is a double oxide structure of aluminium oxide and GaAs native oxide, both oxides are grown anodically. The fabrication of the device is described and the results of initial measurements on the charging and charge retention properties are presented.     

Subthreshold behaviour of e.s.f.i.-s.o.s. transistors

Theoretical and experimental results are presented which illustrate the influence of various parameters on the subthreshold behaviour of e.s.f.i.-s.o.s. transistors. The numerical analysis accounts for the thin silicon film and the existence of a second interface. A comparison is made with a corresponding bulk transistor, furthermore, between a two- and a one-dimensional analysis of e.s.f.i.-s.o.s. m.o.s.t. The agreement for real cases is found to be excellent.     

n-channel inversion-mode InP m.i.s.f.e.t.

Capacitance/voltage and m.i.s.f.e.t. inversion-mode f.e.t. data are reported for p-type InP. It is shown that the surface of this material appears to be inverted at zero gate bias and that good inversion-mode (normally-off) device behaviour is possible.     

I.C.-compatible completely planar GaAs m.e.s.f.e.t.s. by selective diffusion

Completely planar GaAs m.e.s.f.e.t.s were produced by selective open tube diffusion from tin-doped spin-on SiO2 films. After the diffusion process no change in the surface morphology was observed in the doped regions. The evaluation of saturation currents of the m.e.s.f.e.t.s show very good homogeneity. Isolation between doped areas was excellent. Sample preparation and device results are presented; possible applications are outlined.