Solved by boto in post #7 
              
              
                Okay, I’ve found my error. There is nothing wrong with the DataLoader but with get_specs() function. The following lines were the troublemakers: 
...
if song0 == song1:
   spec1 = spec0
   offset1 = random.randint(0, spec0_x - duration)
   while abs(offset0 - offset1) < self.overlap:
         offset…