Cirrus Logic CS6422 - Manual (Page 20)

CS6422
20
3.5.1 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.
3.5.2 RSTHD - RECEIVE SUPPRESSION THRESHOLD
This parameter sets the threshold for far-end speech detection for disengaging receive suppression.
The speech detector that disengages the receive suppression has its sensitivity controlled by RSThd.
The suppression is inserted into the receive path unless signal from the far-end exceeds the receive
channel noise power by RSThd, in which case speech is assumed to be detected and the suppression
is defeated until speech is no longer detected. Decreasing RSThd to make the speech detector more
sensitive could result in false detections due to spurious noise events which may cause an unpleasant
noise modulation at the near-end. Increasing RSThd makes it robust to spurious noise, but may sup-
press weak far-end talkers. RSThd does not affect the ability of the receive suppressor to attenuate
residual network echo.
3.5.3 NSERMP - NOISE ESTIMATOR RAMP RATE
The background noise power estimators increase at a programmable rate until the background noise
power estimate equals the current input power estimate. The background noise power estimators
quickly track drops in the current input power estimate. Choose large values of NseRmp if the envi-
ronment is expected to have rapidly varying noise levels. Choose small values of NseRmp if the en-
vironment is expected to have relatively constant noise power.
3.5.4 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-duplexor 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. Short values of HDly mimic a more full-duplex like behavior, but may be succepti-
ble to false switching due to echo.
3.5.5 HHOLD - HOLD IN HALF-DUPLEX ON HOWL
This is a control flag which, if enabled, holds the system in half-duplex when a howl event is detected.
The system may transition to full-duplex if the flag is subsequently cleared. The default state of HHold
is ‘disabled’, thus when a howl is detected, the CS6422 will temporarily drop into half-duplex, retrain,
and transition back into full-duplex on its own.
3.5.6 TDSRMP - TX DOUBLE-TALK SUPPRESSION RAMP RATE
When “Tx Double-talk Suppression attenuation” (TDbtS, Register 3) is set to a non-zero value, the
CS6422 will introduce a programmable amount of attenuation into the transmit path during a double-
talk event, that is, when the near-end talker and far-end talker are speaking simultaneously. TDSRmp
controls the decay rate of the transmit double-talk attenuation (the attack rate is ~40 ms).
The ‘slow’ setting of TDSRmp results in an attenuation decay rate of about 1 second. The ‘normal’
setting of TDSRmp results in an attenuation decay rate of about 100 ms.
CS6422
20 DS295F1