No sweep tone on smartphone output

[Viktor S]

DEXP - android10, Xiaomi - android10. There is no sweep-tone at the output of the smartphone, although the signal is visible on the screen. I would be very grateful if you could point out where to look for the cause?

[Carl Reinke]

The test signal is internal to the app; it is not audible.  It is meant to be used for trying out different processing settings on a signal without any external noise.