5.5.2 Double-Talk Echo Tuning
If the single-talk echo is able to get suppressed effectively by the default settings of Double-Talk Threshold and AES Suppression, the double-talk performance can be increased further and fine tuned. The first recommended parameter for the double-talk performance is AES Suppression, which it is suggested to tune from 0x0F to 0x01 (no half-duplex). If the single-talk echo does not appear for the Double-Talk Threshold at 0x0F, the user must adjust the AES Suppression parameter from 0x0C to 0x01.
Increase the AEC MIC gain – To increase the MIC gain, both AES and AEC suppress the echo during double-talk near end speech. For more details, refer to 5.3 Set Send Path Level (Uplink) Step 3. Improving the double-talk performance involves raising the near-end speech energy to make it audible while eliminating the single-talk echo.
Adjust the frequency shaping (see Figure 5-3). If the speaker output level is very loud and echo-to-speech ratio at the microphone input is too high, the way to improve this is to further suppress the low-frequency part of the speaker output. As a result, the echo-to-speech ratio at the low frequency parts of the microphone input is further reduced and can have the better double-talk performance.
Use the handsets to support the full-duplex AEC – Some mobile phones do not support the full-duplex speech communication while connecting with the Bluetooth hand-free devices. In this way, the user cannot obtain a satisfactory full-duplex performance while using these handsets.
- Allow only one channel output (assuming for the stereo speakerphone case). If the distance between the microphone and one of the speaker channels is very close (< 4 cm), the AEC tuning for the full-duplexity becomes very difficult. One simple way is to turn off the closer speaker channel output and only allow the other speaker to output, so that the full-duplexity can be much easier to achieve.