RC7620 audio distorted

Hi,
I have tested the audio of a Sierra Wireless RC7620 device mounted on a mangOH Yellow board.
The RC7620 device has been upgraded with the “RC76xx_Release8_GENERIC_GCF_7620_SWI9X07H_00.08.07.00” firmware.

Here below the response to the ATI command:
Manufacturer: Sierra Wireless, Incorporated
Model: RC7620
Revision: SWI9X07H_00.08.07.00 0ce4c1 jenkins 2021/03/17 02:18:20
IMEI: 353634110179750
IMEI SV: 17
FSN: 7Q1085702611B0
+GCAP: +CGSM

I have configured the audio with the following AT commands:
AT!AVCFG=0,0,1
AT!AVSETPROFILE=0,0,0,0,5,0
AT!AVRXG=0,2000
AT!AVTXG=0,2000
AT!AVEC=0,0

In order to test the audio:

  • I activate the audio loopback with the command AT!AVAUDIOLPBK=3
  • I transmit a 1 kHz sine wave to the audio input
  • I expect to receive from the audio output a signal identical to the signal transmitted to the audio input

In such a test, the signal received from the audio output is a distorted 1 kHz sine wave.
As you can see in the attached picture, there’s an interference overlaped to the sine wave.

RC7620_audio_issue

Note that I have acquired the audio using a 48 kHz sampling rate because my application requires wideband audio.

That interference reduces the audio quality, which is important for my application.

Please could you investigate this issue.
Thank you.