| Summary: | 碩士 === 國立高雄第一科技大學 === 電腦與通訊工程所 === 90 === In this thesis, a prototyped digital voice recorder system is designed and implemented. The entire system is realized as a fully stand-alone system. The system is designed with modules, which consists of a AT89C51 microprocessor for human-machine interface control, a low cost 16 bits fixed-point ADSP-2181 DSP for real time speech analysis and synthesis, a low power dissipation LCD module for display, and a non-volatile storage media SmartMediaTM CARD for mass storage. The system has been interfaced to a PC through the RS232 serial port for speech parameters storage. Two types of speech coders are implemented a - law compander puts emphasis on the reconstructed speech quality, and a LPC coder provides the long-time speech parameters storage.
In the system, several techniques are used to fulfill requirements in a real time LPC speech coder. First, we fully utilize the Autobuffering mode of ADSP-2181 DSP’s serial port and dual buffer system in real-time implementation. Second, we apply a single chip microcontroller to coordinate high speed DSP with a low speed memory card to avoid lost of speech parameters. Finally, the technique of modified autocorrelation method is exploited to reduce computational complexity for pitch detection and the fixed-point LPC speech coder is coded by the assembly language of ADSP-2181 DSP in order to achieve real time speech compression.
Experimental results show that the fixed-point LPC speech coder can maintain a tolerable speech quality at 2.4Kbps bit rate. Integrated with a - law compander, the digital voice recorder system can execute in real time and hold excellent speech quality.
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