What you hear is what was recorded in On April 27, 1935 in the Ludwigshaven Theater using the pictured AEG Magnetophon prototype. Four different prototypes were built between 1932 and 1934, and this is the last one. It should have been exposed in the 1934 Berlin Radio Fair, but still had some troubles, especially a major design issue where the tape would break if you did not wait until the reels stop before playing/rewinding. There was no fast forward and the capstan motor was asynchronous, hence audible pitch variation. Its improved successor became the Magnetophon K1 (which is a visually different machine).
The cuts, pitch variations and other sound "defects" are authentic. The tape used was the early gray Carbonyl Iron type, quickly replaced by black Fe3O4 tapes in 1936. The tape speed was 1 meter per second (100cm/s).
Source and Credit :- https://www.youtube.com/watch?v=OA1oDxRo_lI&feature=youtu.be