Microchip has introduced a speech encoding (compression) and decoding (decompression) library for its 16-bit dsPIC digital signal controllers (DSCs). The dsPIC30F Speech Encoder/Decoder Library enables embedded designers to transmit more messages over a given bandwidth or store longer amounts of speech in a given memory space, while maintaining superior sound quality and intelligibility.
This library is based on the Speex (www.speex.org/fsos.html) open source compression format and achieves a 16:1 compression ratio and toll quality speech (PESQ 3.7-4.2).
Many design engineers are seeking to add speech compression to their bandwidth or memory-constrained applications, but have opted for lower compression methodologies to avoid a stiff per-unit royalty for the intellectual property. Microchip says that the adoption of the open-source Speex audio compression format in the dsPIC30F library offers a significant cost reduction over competitive options and brings non-royalty bearing 8 Kbps encoding to the embedded world. Any embedded application that transmits voice over limited bandwidth or has memory constrained playback can benefit from this speech compression/decompression library.
Some product applications are, VoIP, tapeless answering machines, voice announcement systems, medical equipment, building and home safety systems, intercoms and proprietary communications equipment.
This library has a well-documented application programmer's interface (API) that makes it easy to incorporate speech functions into an application. It also supports optional voice activity detection. The speech encoder samples data at 8 kHz, using either the dsPIC DSC's on-chip 12-bit ADC or a 16-bit input obtained from an external codec, via the on-chip codec interface port. The encoder achieves up to a 16:1 compression ratio and generates a fixed 8 Kbps output rate.
Output of decoded speech can be accomplished using the dsPIC DSC's standard PWM or via the interface to an external Codec. The encoder requires 19 MIPS (worst case), 33 Kbytes of program memory and 6,2 Kbytes of RAM. The decoder requires 3 MIPS, 15 Kbytes of program memory and 3,2 Kbytes of RAM. Storing speech requires 1 Kbyte of memory for each second of speech.
The library permits the compressed speech data to be stored in on-chip memory (Flash, EEPROM or RAM) or to an external Flash memory. Playback-only applications can benefit from a PC-based speech encoder utility that is included on the library CD. This utility creates encoded speech files from a PC microphone or WAV files.
The following dsPIC DSCs have the on-chip resources needed for this library: dsPIC30F5011/3, dsPIC30F6011/2/3/4.
For more information contact Arrow Altech Distribution, +27 (0)11 923 9600, Avnet Kopp, +27 (0)11 809 6100, Memec SA, +27 (0)21 674 4103, or Tempe Technologies, +27 (0)11 452 0530.
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