Speech library tackles tough quality and cost constraints - Embedded.com

Speech library tackles tough quality and cost constraints


Chandler, Ariz.—A speech encoding and decoding library geared for Microchip Technology Inc.'s dsPIC digital signal controller combines high compression ratio, toll-quality speech, and royalty-free purchasing. The library is a welcome addition for embedded system designers working with limited bandwidth or memory.

Specifically, the library, dubbed dsPIC30F, touts a 16-to-1 maximum compression ratio, which compared to lower compression methods lets you transmit more messages for a given time and bandwidth or store longer messages in a given amount of memory. As for sound quality and intelligibility, the library achieves a PESQ score (Perceptual Evaluation of Speech Quality) score of 3.7 to 4.2. And because the library is based on the Speex open source audio-compression format, it is offered royalty-free for a one-time licensing fee.

The library's speech encoder samples data at 8 kHz using either the dsPIC's on-chip 12-bit analog-to-digital converter or a 16-bit input from an external codec. The output of the encoder is a compressed 8-kbits/s stream. Encoding requires 19 MIPS (worst case), 33 kbytes of program memory, and 6.2 kbytes of RAM. One second of speech fills 1 kbyte of on-chip or external EEPROM, RAM, or flash memory. Decoding is achieved using the dsPIC's PWM technique or an external codec and requires 3 MIPS, 15 kbytes of program memory, and 3.2 kbytes of RAM.

The library includes a well-documented API for easy access by the application, as well as an optional ability to detect voice activity. For playback-only applications, the library also includes a PC-based utility that encodes speech files originating from a microphone or WAV file.

Among the dsPIC digital signal controller models having the resources to run the library are the dsPIC30F5011, dsPIC5013, and the dsPIC6011 to dsPIC6014.

A one-year evaluation and development version of the dsPIC30F sells for $5 and can be purchased online. Production versions of the library start at $2,500 for 5,000-unit productions. Contact the factory for addition pricing options. The library is available now.

Microchip Technology Inc. , 1-888-628-6247, www.microchip.com

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