Mute the microphone in M66 module

Hello everyone.
I’m working on a M66 module using OpenCPU SDK.
Sometimes I need to mute the microphone completely. I used below command from RIL library, but still I can hear some voices over a phone call:

Moreover, I couldn’t find any AT command that fits the purpose.
Now, I’m searching for a solution, I’d appreciate any help.


Do you use an external amplifier circuit?

Is the channel of the first parameter in the “RIL_AUD_SetVolume” function set correctly?

No, I’ve not used external amplifier. My circuit is based on the hardware design document provided by Quectel:

And the first argument is also correct. It must be from this enum, defined in ril_audio.h:

typedef enum {
    VOL_TYPE_MIC      ,   /* microphone attribute */
    VOL_TYPE_SPH      ,   /* MMI can apply to associate volume; speech sound attribute */
    VOL_TYPE_MEDIA    ,   /* MMI can apply to associate volume; As MP3, Wave,... attribute */
    VOL_TYPE_SID      ,   //side tone attribute