Musicam Roadrunner Manual do Utilizador descarregar pdf (Página 22)

Prima LT USERS GUIDE

6-226-22

commands. In general, it is better to use scale factor protection if the

data channel is noisy (high BER). Scale factor protection (ESP) is used

for all ISO/MPEG Layer II types of bitstreams. Scale factors are the

levels of the digital audio signal within a sub-band. There are 32 sub-

bands and the scale factors change the level over a 120 dB range. An

error on any scale factor will cause a perceptible impairment in the

audio. To prevent this, scale factor protection can be inserted at the

encoder and if the decoder is capable of recognizing it, then the decoder

can perform a concealment operation to repair the damaged scale

factor. If the decoder does not know about scale factor protection, the

audio is decoded and any damaged scale factors cause an impairment.

Scale factor protection is not bi-directional, and must be enabled

independently for each direction. If ESP has enabled scale factor

protection, the far end decoder must enable scale factor correction

with the DSP command. If only one end has scale factor protection

enabled, audio may be muted. The Prima LT’s Scale factor protection

is not compatible with other manufacturers codecs. Scale factor

protection is compatible with MUSICAM USAs CDQ2001 and CDQPrima

line of codecs.

6.1.5.8 A/D And D/A Calibration

MENU NAVIGATION COMMAND WINDOWS RC DESCRIPTION

DDA N/A Calibrate D/A converter

EAD Calibrate A/D converter

The decoder Digital to Analog (D/A) converter can be calibrated by the

DDA command. This calibration process assures that the D/A converter

is operating optimally. The analog input A/D converter is calibrated by

the EAD command. This calibration is performed automatically at

power-up but can be manually performed at any time. The calibration

process removes the effect of any DC voltage offset present at the input

of the A/D converter. This has a minor positive effect on the audio

compression algorithm. It may be beneficial to re-calibrate after an

audio source has been changed.

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