Study And Design On Multi-Band Excited Coder Based On FPGA

Directly digitizing of speech signals needs too much high bit rate in digital speech communication, thus compression and coding of the speech signals is essential in the process to increase the efficiency of transmission and storage, as well as the channel capacity. By reducing coding rate, more speech signals can be transferred in the same channel. So, Low Bit Rate Speech Coding has especially important significance when the transmission rate is limited very strictly.FPGA has become the best selection in the design of complex digital system in modern design process of digital system,especially in communication system, because of its merits like high integration, better reliability, short design period, less investment and agility. The usage efficiency of FPGA for communication system can be raised by designing low rate speech coder in FPGA.The research and design of multi-band excitation vocoder based in FPGA is expatiated in this thesis. Firstly, it introduces the development of speech coding, along with the significance of the low bit rate speech coding. It also compares the model of traditional dualistic excitation LPC vocoder and the multi-band excitation vocoder, and lucubrates the analytical method of frequency domain and time domain in the parameter extraction of multi-band excitation vocoding. Secondly, based on the parameter extraction operation of keynote cycle, it adopts time domain in rough estimate operation of keynote and frequency domain in fine estimate operation of keynote, in according to the immediacy required in practice, to minish operation amount. After having the keynote cycle, it separately processes harmonic waves of speech band; whereafter takes V/U judgement/verdict and amplitude estimate to each band. The speech can be composed by transmitting the information of keynote cycle, V/U judgment and amplitude estimate to decoder. We select FPGA of type xc3s200 as hardware to design the coder and display the hardware resources inside, moreover study the method and steps of designing DSP, based on FPGA, by using system generator,Finally, it emphasizes the design process of multi-band excitation vocoder. We can work out the module of high pass filter and the module of low pass filter, module of divide frame, module of keynote rough estimate, module of keynote fine estimate, module of band-separated V/U judgment/verdict and module of band-separated amplitude estimate, by using simulink, ISE and system generator...