The link. I've notice about the giant factory of 30.000 workers, Is it real? The voice of A. is different than what I'm used in the speeches. More calm, more charm.
There is nothing secret about it, you can't miss the microphones. It is also the only known recording of Hitler speaking in his "normal" voice...Not the "Stage" voice he used in his speeches. There have been a few videos that have examined this in detail.
The German soldiers removed the microphone as they noticed it. Also the Hitler´s voice was used for thre "downfall" movie as Bruno Ganz used the voice for his part as Hitler.
There was a doco many years ago that used Hitler's tape, computerized lipreading, and dubbing to put Hitler's voice onto some of the silent home movies of him. Pretty interesting stuff.