Microchip Technology dsPIC33F Family Manual de usuario descargar pdf (Pagina 55)

dsPIC33F

11.9 Noise Suppression Library

The dsPIC DSC Noise Suppression Library provides a

function to suppress the effect of noise interfering with

a speech signal. This function is useful for microphone-

based applications which have a potential for incoming

speech getting corrupted by ambient noise captured by

a microphone. It is especially suitable for systems in

which an acoustically isolated noise reference is not

available, such as:

• Hands-Free Cell Phone Kits

• Speakerphones

•Intercoms

• Teleconferencing Systems

• Headsets

• As a front end to a Speech Recognition or Speech

Encoding system

• Any microphone-based application that needs to

eliminate undesired noise

• Any application that needs to eliminate noise

interference from signals received over a

communication channel

The Noise Suppression Library uses an 8 kHz sampling

rate. However, the library includes sample rate

conversion functions that ensure interoperability with

libraries and speech sampling peripherals configured for

higher sampling rates (9.6 kHz, 11.025 kHz or 12 kHz).

Key features of the Noise Suppression Library include:

• All functions can be called from either a ‘C’ or

assembly application program

• Full compliance with the Microchip C30

C Compiler, Assembler and Linker

• Precompiled library archive files

• Highly optimized assembly code, utilizing DSP

instructions and advanced addressing modes

• Audio Bandwidth: 0-4 kHz at 8 kHz sampling rate

• 10-20 dB noise reduction depending on type of

noise

• “dsPIC30F Noise Suppression Library User’s Guide”

• Demo application source code is provided

• Accessory Kit available for purchase includes:

audio cable, headset, oscillators, microphone,

speaker, DB9 M/F RS-232 cable, DB9M-DB9M

null modem adapter and can be used for library

evaluation

TABLE 11-5: RESOURCE REQUIREMENTS

11.10 Acoustic Echo Cancellation Library

The Acoustic Echo Cancellation (AEC) Library

provides a function to eliminate echo generated in the

acoustic path between a speaker and a microphone.

This function is useful for speech and telephony

applications in which a speaker and a microphone are

located in close proximity to each other and therefore,

susceptible to signals propagating from the speaker to

the microphone resulting in a perceptible and

distracting echo effect at the far end. It is especially

suitable for these applications:

• Hands-Free Cell Phone Kits

• Speakerphones

•Intercoms

• Teleconferencing Systems

For hands-free phones intended to be used in compact

environments, such as a car cabin, this library is fully

compliant with the G.167 standard for Acoustic Echo

Cancellation.

Like the Noise Suppression Library, the Acoustic Echo

Cancellation Library also includes sample rate

conversion functions.

Key features of the AEC Library include:

• All functions can be called from either a ‘C’ or

assembly application program

• Full compliance with the Microchip C30

C Compiler, Assembler and Linker

• Precompiled library archive files

• Highly optimized assembly code, utilizing DSP

instructions and advanced addressing modes

• Echo cancellation for 16, 32 or 64 ms echo delay

or ‘tail length’ (configurable)

• Fully tested for compliance with G.167

specifications for in-car applications

• Audio Bandwidth: 0-4 kHz at 8 kHz sampling rate

• Convergence Rate: up to 43 dB/sec.,

typically > 30 dB/sec.

• Echo Cancellation: Up to 50 dB, typically > 40 dB

• “dsPIC30F Acoustic Echo Cancellation Library

User’s Guide”

• Demo application source code is provided

• Accessory Kit available for purchase

TABLE 11-6: RESOURCE REQUIREMENTS

Algorithm MIPS Flash RAM

Noise Suppression 3.3 7 KB 1 KB

Sample Rate Conversion 1.0 2.6 KB 0.5 KB

Note: The user application might require an

additional 1 KB-1.5 KB for data buffering

(application-dependent).

Algorithm MIPS Flash RAM

AEC – 64 ms Echo Tail 16.5 6 KB 5.7 KB

AEC – 32 ms Echo Tail 10.5 6 KB 3.4 KB

AEC – 16 ms Echo Tail 7.5 6 KB 2.6 KB

Sample Rate Conversion 1.0 2.6 KB 0.5 KB

Note: The user application might require an

additional 2 KB-2.5 KB for data buffering

(application-dependent).

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