In “Zoom G16” such characteristics: Input Level -50dBm to +4dBm continuously variable.
Also it has an attenuator which regulates the level of the input signal. I thought that they and regulated by the value of -50 dBm to 4 dBm.
The distortions have occurred even if the position of the handle to the left.
As far as I understand, value dBm and dBu not be converted into each other.