CDB6420 Просмотр технического описания (PDF) - Cirrus Logic

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CDB6420

Full-Duplex Speakerphone Chip

Cirrus Logic 

CS6420

RHDet - Receive Half-Duplex Detection

Threshold

The sensitivity of the speech detector controls

channel switching and ownership in half-duplex

mode. The receive speech detector registers speech

if the receive channel signal power is RHDet above

the noise floor for the receive channel.

HDly - Half-Duplex Holdover Delay

After a channel goes idle in the half-duplex mode

of operation, a change of channel ownership is in-

hibited for HDly in order to prevent false switching

due to echoes. The half-duplex will be more im-

mune to false switching if this delay is longer, but

it will also prevent a fast response to legitimate

channel changes.

NseRmp - Background Noise Power Estimator

Ramp Rate

The background noise power estimators increase at

a rate of 3 dB/NseRmp until the background noise

power estimate equals the current input power esti-

mate. The background noise power estimators

quickly track drops in the current input power esti-

mate. Choose small values of NseRmp if the envi-

ronment is expected to have rapidly varying noise

levels. Choose large values of NseRmp if the envi-

ronment is expected to have relatively constant

noise power.

RSThd - Receive Suppression Threshold

This parameter sets the threshold for far-end

speech detection for disengaging receive suppres-

sion. The speech detector that disengages the re-

ceive suppression has its sensitivity controlled by

RSThd. The suppression is inserted into the receive

path unless signal from the far-end exceeds the re-

ceive channel noise power by RSThd, in which

case speech is assumed to be detected and the sup-

pression is defeated until speech is no longer de-

tected. Decreasing RSThd to make the speech

detector more sensitive could result in false detec-

tions due to spurious noise events which may cause

an unpleasant noise modulation at the near-end. In-

creasing RSThd to make it robust to spurious noise,

but may cause weak far-end talkers to not be heard.

RSThd does not affect the ability of the receive

suppressor to attenuate residual network echo.

PCSen- Path Change Sensitivity

The Acoustic Interface is likely to have many path

changes, for example, as people move about in the

room where the full-duplex speakerphone is being

used. The sensitivity of the path change detector

can be changed with the PCSen Bit. Set PCSen to 0

for high sensitivity and 1 for low sensitivity.

If PCSen is set to high, extended doubletalk may

cause the CS6420 to briefly drop into half-duplex.

When PCSen is set to low, brief echo may be heard

during path changes.

DS205PP2

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