Also even if you program your Litchi flight to maintain the drone's altitudes above each waypoint as it is crossed, meaning above the terrain at the drone's current position along the flight path, as opposed to having altitudes referenced to the launch point, the audio altitude callouts will always be referenced to the launch point, and not to the current location of the drone along its waypoint flight path.
This means if, for example, you set a fixed altitude of 150 feet above terrain level, flying the drone over land that lies below the launch point will mean that those periodic altitude callouts will be LESS than the pre-programmed 150 feet AGL. Litchi tends to fly the drone a tad higher than specified when the flight path is vectored over lower-lying terrain than the launch point.
It is well worth mentioning also that if the drone's waypoint mission takes it over terrain whose altitude is higher than the launch point, Litchi tends to fly the drone significantly LOWER than the altitude that was specified in creating the waypoint mission, which could result in the drone hitting a tree or building if that margin of error is not factored in during the creation of such a flight path.
But for the saving grace of my Mavic Pro's collision avoidance safety net, I would have lost that drone to a palm tree looming just 50 feet high during a waypoint mission flown some time ago, despite my having set the altitude to be 150 feet above ground level at the drone's position along the flight path. Had I flown my Phantom 3 Standard along that same route, it would have careened into that tree for sure, since that old drone has no obstacle avoidance features.