33FJ128GP708 datasheet(57/90 Pages) MICROCHIP

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Preliminary

DS70155C-page 55

dsPIC33F

11.13 Speech Encoding/Decoding

Library

The Speech Encoding/Decoding Library performs toll-

quality voice compression and voice decompression.

The library is based on a modified version of the Speex

speech encoder/decoder source code and features a

16:1 compression ratio. It samples speech at 8 kHz and

compresses it to a data rate of 8 kbps. Storing

compressed

speech

for

playback

requires

approximately 1 KB of memory for each second of

speech. The library is especially suitable for the

following voice-based applications:

• Answering Machines

• Building and Home Safety Systems

•Intercoms

• Smart Appliances

• Voice Recorders

• Walkie-Talkies

• Any Application using Message Playback

A PC-based speech encoder utility program allows you

to create your own encoded speech files for playback.

Encoded speech files are made from either a PC

microphone or existing WAV file. Once you create the

encoded speech files, they are added to your MPLAB

C30 project, just like a regular source file, and built into

your application. The speech encoder utility allows you to

select four target memory areas to store your speech file:

program Flash memory, RAM and external Flash

memory. External Flash memory allows you to store

many minutes of speech (1 minute of speech requires

60 KB) and it is supported through a general purpose I/O

port.

Key features of the Speech Encoding/Decoding Library

include:

• PESQ-based Mean Opinion Score: 3.7-4.2

(out of 5.0)

• Code Excited Linear Prediction (CELP) based

coding

• 2 Analog Input Interfaces – codec or on-chip ADC

• 2 Analog Output Interfaces – codec or

on-chip PWM

• Optional Voice Activity Detection

• Storing compressed speech requires 1 KB of

memory per second of speech

• Royalty-free (only one-time license fee)

• Full compliance with Microchip MPLAB C30

C Compiler Language Tools

•

“dsPIC30F Speech Encoding/Decoding Library

User’s Guide”

• Designed to run on dsPICDEM 1.1 General

Purpose Development Board (DM300014)

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