Digital Voice Systems VC-20-ATC-10B Especificaciones descargar pdf (Pagina 76)

FAA20 Embedded NEXCOM Vocoder

Board Manual

This manual has been prepared for the Federal Aviation Administration.

FA100-00107 (March 2004) – Rev 1.0.0 Page 70

8.3.6 CLKREF

The CLKREF command sets the port which will be used to control timing for

the linear voice processor (LVP) task. The LVP is called after 5 samples

are received on the reference port.

Table 17: CLKREF Command Syntax

ATTRIBUTE DESCRIPTION

SYNTAX CLKREF [port]

PARAMETERS port PCM = Digital Data Port

AUD = Audio Port (default).

FLASH YES

Print current clock reference setting.

COM1: clkref

> CLKREF AUD

EXAMPLES

Set clock reference to PCM port.

COM1: clkref pcm

> CLKREF PCM

For best vocoder results, this reference should be set equal to the primary

port being used with the vocoder. For example, when the PCM port is

routed to the vocoder, the CLKREF parameter should be set to PCM.

If this setting is not configured properly, timing differences may cause the

FAA20 to insert or delete samples in the primary voice data path. For

example, if the FAA20 is configured to receive voice data on the PCM port

(in external timing mode) and the CLKREF parameter is set to AUD, the

LVP will be timed to the AUD interface (internal timing). With two different

timing references, samples will be accumulated or depleted eventually

causing an insert or drop on a periodic basis that is related to the timing

difference.

This setting does not affect FAA20 operation when the TEST BITEXACT

parameter is set. When this parameter is set, the vocoder does not operate

in real time; thus, adjustments for timing differences are not required.

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Digital Voice Systems VC-20-ATC-10B Especificaciones Pagina 76