Cirrus Logic CS6422 - Manual (Page 2)

CS6422
2 DS295TB2
is not detected), and AuNECD should be set to
‘0’ (this allows the NEC to be enabled after it
has been disabled by NFNse).
3) Transmit Noise Guard. Transmit noise guard is
a noise squelch feature that introduces attenua-
tion (set by TSAtt) in the transmit channel
when the near-end is silent. This prevents un-
wanted noise (from a car or other noisy envi-
ronment) from being transmitted to the far-end
listener. Noise guard is enabled by default, and
is disabled by setting TSMde to a ‘1’.
4) Double-talk Attenuation. Double-talk Attenua-
tion introduces a programmable amount of loss
into the transmit and/or the receive path during
full-duplex double-talk. This feature enhances
system stability in hands-free full-duplex to
hands-free full-duplex conversations by limit-
ing the gain in the acoustic coupling loop, al-
lowing for higher volume levels at both ends of
the connection.
Two parameters (TDbtS and RDbtS) control
the amount of attenuation that is added to the
transmit and receive channels, respectively.
Double-talk attenuation is disabled by default
(both attenuators are set to 0 dB).
The decay rate of the attenuation is config-
urable through TDSRmp and RDSRmp for the
transmit and receive channels respectively.
Both of these parameters default to the ‘slow’
setting which provides a decay rate of about 1
second. Most implementations should use the
'normal' setting, which provides a decay rate of
about 250 ms.
5) Programmable Sidetones. The parameters ASdt
and NSdt allow for a digital path to be created
between AO and APO (ASdt) or NO and NI
(NSdt). These digital paths are superimposed
on the real acoustic or network paths and are
canceled by the appropriate echo canceller. In
certain environments, most notably the car en-
vironment where the acoustic path is weak, in-
consistent, or distorted, the presence of a strong
linear path can enhance system performance.
Both acoustic and network sidetones are dis-
abled by default.
6) Test features. The CS6422 contains a number
of features that are useful in the design and de-
bug stages of a system. Separate disable con-
trols (AECD and NECD) allow the acoustic
path and the network path to be debugged and
tested independently. HwlD and TD allow the
howl detector and tone detector to be disabled.
APCD and NPCD allow the acoustic and net-
work path change detectors to be disabled, forc-
ing each canceller to train out of a path change
rather than training from a cleared state on a
major path change. APFD and NPFD allow the
pre-emphasis filters on the acoustic and net-
work echo cancellers to be disabled. This en-
hances results when testing ERLE performance
with white noise.
REVISION HISTORY
Revision Date Changes
TB1 JAN 1999 Initial release.
TB2 MAR 2006 Update company contact information.