Microchip Technology dsPICDEM MCLV-2 Manual de usuario descargar pdf (Pagina 27)

16-bit Embedded Control Solutions

Noise Suppression Library

This application library suppresses the noise interference

in a speech signal, such as ambient noise picked up by

a microphone while capturing speech. This algorithm

is particularly useful for systems such as hands-free

phones, speakerphones, intercoms and headsets where

an isolated noise reference is not available. The algorithm

handles 0–4 kHz audio bandwidth and provides adjustable

noise reduction up to 44 dB.

Acoustic Echo Cancellation Library

This library provides a function to eliminate the echo

generated in the acoustic path between a speaker and a

microphone, such as in a speakerphone or an intercom

system. This library is compatible with the G.167

standard and provides 16, 32, 64 or 128 ms echo delays.

It handles 0–4 kHz audio bandwidth and provides echo

cancellation of 40–-50 dB. It also includes some sample

rate conversion functions.

Line Echo Cancellation Library

This library provides a function to cancel electrical line

echoes caused by 2- to 4-wire conversion hybrids in

telephone lines. The library can be used in long distance

voice communication applications, especially in links

involving satellite networks and intercontinental long haul

networks, as well as digital networks, such as Voice over

IP (VoIP). This library is compatible with the ITU-T G.168

recommendation. The library can be used for full-duplex

operation. It handles 0-4 kHz audio bandwidth (8 kHz

sampling of 16-bit speech data).

Equalizer Library

The Equalizer library allows applications to change

the tonal properties of a signal by offering an 8-band

frequency band amplitude control. The library processes

an 8 kHz sampled signal. The library works readily with

the rest of Microchip’s dsPIC DSC Speech and Audio

Processing Algorithms.

Libraries for Speech and Audio Applications

Speech Encoding/Decoding Libraries

Three options exist for a variety of speech compression/encoding and decompression/decoding applications:

■ The library is an implementation of the ITU-T G.711 standard which uses A-law or μ-law companding to

achieve 2: 1 compression.

■ G.726A is an implementation of the ITU-T G.726 Annex A standard which uses Adaptive Differential Pulse Code

Modulation (ADPCM) encoding algorithm. It can achieve up to an 8:1 compression ratio depending on output bit

rate selected.

■ Speex is a popular standard in the open source software community which has been adapted for the dsPIC DSC.

It uses Code Excited Linear Prediction (CELP) algorithm. It can achieve a 26:1 compression ratio.

Vocoder

Incoming Data

Rate (16-bit)

Output Rate

Speech Quality

(MOS)

MIPS

(1)

Flash (KB) RAM (RB) Target

G.711 8 kHz 64 kbps 4.3–4.5 1 3 3.6

PIC12/dsPIC®

DSC

G.726A 8 kHz 16–40 kbps 4.3–4.5 15 6 4 dsPIC DSC

Speex 8/16 kHz 8–12.8 kbps 3.7–4.2 20/24 24/38 7.6/12 dsPIC DSC

Note 1: Includes both encoder and decoder processing in full duplex.

dsPIC DSC Automatic Gain Control Library

The dsPIC DSC Automatic Gain Control Library

automatically adjusts the amplitude of a speech signal to

match a set level. This is useful in speech applications

where the distance between the speech source and the

microphone is not fixed. The Automatic Gain Control

Library can be used readily with Microchip’s Speech and

Audio Solutions for speech signal pre-processing.

Speech and Audio Fast Forward (SAFF)

The dsPIC DSC Speech and Audio Fast Forward tool

provides user’s with real-time control of Microchip’s Speech

and Audio Processing Algorithms as they are running in a

embedded system application. This PC GUI tool facilitates

code generation and easy tuning of Microchip’s Noise

Suppression, Acoustic Echo Cancellation, Line Echo

Cancellation and Equalizer algorithms in speech and audio

applications by simplifying parametric tuning of algorithms.

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