Speech Data Compression for Embedded Systems

The main concern of this paper is speech data compression for low-cost embedded systems such as voice-related toys or devices with interactive sound-responses. We use a PC to generate and compress 8-bit-speech-data that has various features such as human speech, symphony and animal songs; the compressed data are then transferred to a masked-ROM. An Intel 8051 embedded chip is employed to expand the compressed speech data stored in a masked-ROM with size ranging from 1 8 Mega Bytes. No RAM ( read/write memory ) is available in the system ( to reduce production cost 1. The ROM also stores the program that is responsible for expanding the compressed data. Since the compression is done off-line, we use simple vectorquantization techniques to perform a first stage lossy compression of the data; the lossy-compressed data are then treated by a second stage lossless compression. Because of the the lack of RAM in the expansion stage, an LZ compression technique cannot be applied. Instead, we use a runlengthHuffman encoding scheme coupled with a unary-code to perform the lossless compression. Also, because of the slow processing speed of the processor in the expansion stage, a length-limited Huffman code must be used. Instead of using the common package-merge[ll algorithm to obtain the lengthlimited code, we develop a technique that uses splaying to achieve the goal.