CS6422 Cirrus Logic, Inc., CS6422 Datasheet - Page 16

• Manufacturer Part Number: CS6422
• Description: Evaluation board
• Manufacturer: Cirrus Logic, Inc.

3.3.6
3.3.7
16
ACC - ACOUSTIC COEFFICIENT CONTROL
TSMDE - TRANSMIT SUPPRESSION MODE
The coefficients of the AEC adaptive filters in the CS6422 are controlled by ACC. The default position
(00) yields normal operation, which means the coefficients are free to adjust themselves to the echo
path in order to cancel echo. When set to the clear position (01), the adaptive filter coefficients are all
held at zero, so the echo canceller is effectively disabled. Note that unless the half-duplex mode is
disabled, this will force the CS6422 into half-duplex mode. The freeze position (10) causes the coef-
ficients to retain their current values and not change.
TSMde enables the Noise Guard feature of the CS6422. Noise Guard is a noise squelch feature that
operates in the transmit path (from the near-end microphone to the far-end speaker). In traditional
hands-free systems where the near-end talker is located in a noisy environment, the near-end system
will remain in transmit mode and send that noise to the far-end listener. This creates a real problem
if the listener is using a traditional half-duplex speakerphone because the far-end phone will stay in
receive mode, thus preventing the far-end talker from being heard. Noise Guard eliminates this prob-
lem by squelching the transmit channel at the near-end unless near-end speech is detected, permit-
ting the far-end speakerphone to switch normally during the conversation.
Noise Guard is also useful in cellular hands-free car applications because it prevents car noise from
reaching the far-end while the near-end talker is silent.
Noise Guard is usually disabled when “half-duplex Idle return-to-Transmit” is enabled. See the Reg-
ister 2 description for more information. Noise Guard is enabled by default.
CS6422