Solved by JuanFMontesinos in post #3 
              
              
                __getitem__ is the process which is spawn with multiprocess. 
The workload should be there (mainly the spectrograms) 
As @hash-ir mentions, any other task can be performed in the __init__ function (or even outside the dataset class) 
It’s all about how many RAM do you have. 
Do you need to read audi…