I used a phone that can record from a call. I called it with L5 and Samsung A50 playing the same song with strong speaking and low music. The files then are passed from sox to produce the spectrograms. It is clear that “someone” using a software cuts the sound sent over the phone at 4KHz. The cut for L5 is so uniform that I am sure it is not done by the hardware. Some software does this damage. On the contrary notice that the L5 mic behaves as superior to Samsung’s A50, as the latter does not pass the music which is lower than speech for this song at seconds around 10, 16, 22 etc. It produces silence. This is not observed with L5. Here are the spectrograms:
L5:
Samsung A50:
So @dos do you know what causes this behavior and how can be resolved improving L5’s audio perception on the other side?