Cirrus Logic CS6422 - Manual (Page 18)

CS6422
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3.4.1 THDET - TRANSMIT HALF-DUPLEX DETECTION THRESHOLD
The sensitivity of the speech detector controls channel switching and ownership in half-duplex mode.
The transmit speech detector registers speech if the transmit channel signal power is THDet above
the noise floor of the transmit channel.
3.4.2 TAPS - AEC/NEC TAP ALLOCATION
The CS6422 has a total of 63.5 ms of echo canceller taps that it can partition for use by the network
and acoustic echo cancellers. By default, the CS6422 allocates 39.5 ms for the AEC and 24 ms for
the NEC. See NErle, NFNse, AErle, and AFNse in Register 4, and AECD and NECD in Register 5 for
more options when an echo path is nonexistent.
3.4.3 TVOL - TRANSMIT VOLUME CONTROL
Volume in the transmit path is controlled by TVol. Like receive volume, the transmit volume is con-
trolled by an AGC. See RVol in Register 0 for more details. The default setting for TVol is +0 dB.
3.4.4 RSD - RECEIVE SUPPRESSION DISABLE
The Receive Supplementary Echo Suppression function is a non-linear echo control mechanism.
Supplementary Echo Suppression attenuates signals in the receive direction by 24 dB when far-end
speech is absent in the receive path. The attenuation is released only when the receive channel is
active. By default, the receive suppression function is enabled.
3.4.5 NCC - NETWORK COEFFICIENT CONTROL
The NEC adaptive filter’s coefficients are controlled by NCC. See ACC in Register 0 for more details.
The default setting for NCC is Normal mode.
3.4.6 AUNECD - AUTO RE-ENGAGE NEC DISABLE
AuNECD works in conjunction with NFNse in the determination of whether the Network Echo Cancel-
ler should be enabled or disabled. If the CS6422 determines that a network coupling path does not
exist and disables the NEC (which can occur only if NFNse is set to a non-zero value), then AuNECD
allows the DSP to re-enable the NEC if at some point during the call a network path appears.
An example occurs in a digital PBX environment. Initially, a 4-wire ‘intercom’ call is placed between
two stations. The CS6422 at the near-end determines that a network path is not present and disables
the NEC. During the call, one of the stations conferences in a call from an external analog line. A
network coupling path is introduced by the addition of the analog line due to the impedance mismatch
at the 2-to-4 wire converter. If AuNECD is enabled, the CS6422 at the near-end will detect the pres-
ence of the network coupling path and re-enable the NEC automatically, drop to half-duplex, and re-
train.
CS6422
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