Improving audio quality.

General rules.

• output gain - try to set as low as possible.
• microphone gain - try to set as low as possible.
• echo cancellation - turn off if possible.
• noise suprpression - turn off if possible.
• sidetone - turn off or set to minimum.

See also: Sending AT commands via socat and chat.

Quectel EC25-E.

AT+QRXGAIN=16384
AT+QMIC=16384,1024
AT+QAUDMOD=3
AT+QSIDET=0

AT Command	Description
AT+QRXGAIN	Set downlink gain
AT+QMIC	Set uplink gain
AT+QAUDMOD	Set audio mode
AT+QSIDET	Set the side tone gain
AT+QAUDCFG="fns"	Enable/Disable noise suppression

SimCOM SIM7600X-H.

AT+COUTGAIN=8
AT+CMICGAIN=3
AT+CECM=0

Basic AT commands.

AT Command	Description
AT+COUTGAIN	Adjust out gain (0-8)
AT+CMICGAIN	Adjust mic gain (0-8)
AT+CECM	Adjust echo canceller

Additional AT commands.

These commands may be executed during a call only.

AT Command	Description
AT+CRXVOL	Adjust RX voice output speaker volume
AT+CTXVOL	Adjust TX voice mic volume
AT+CTXMICGAIN	Adjust TX voice mic gain
AT+CNSN	Mic noise suppression
AT+CNSLIM	Mic noise suppression
AT+CECH	Inhibit far-end echo
AT+CECDT	Inhibit echo during doubletalk
AT+CECWB	Inhibit echo in the high band
AT+CECRX	Enable or disable VOICE_MOD_ENABLE

SimCOM SIM900.

AT+CLVL=100
AT+CMIC=0,0
AT+ECHO=0,0,0,0
AT+SIDET=0,0

AT Command	Description
AT+CLVL	Loud speaker volume level
AT+CMIC	Change the microphone gain level
AT+SIDET	Change the side tone gain level
AT+ECHO	Echo cancellation control

See also: Using chan_quectel with SIM900 board with analog input/output.

SimCOM A7670X.

This module has a simplified audio path - no echo cacellation, no noise supression. Only output and input gains may be adjusted.

AT+COUTGAIN=4
AT+CMICGAIN=2

Basic AT commands.

AT Command	Description
AT+COUTGAIN	Adjust out gain (0-7)
AT+CMICGAIN	Adjust mic gain (0-7)