code: def transform_first(self, fn, lazy=False):
          
          return super(AudioFolderDataset, self).transform_first(fn, lazy=lazy)
docs: Returns a new dataset with the first element of each sample
          transformed by the transformer function `fn`.
  
          This is useful, for example, when you only want to transform data
          while keeping label as is.
          lazy=False is passed to transform_first for dataset so that all tramsforms could be performed in
          one shot and not during training. This is a performance consideration.
  
          Parameters
          ----------
          fn : callable
              A transformer function that takes the first element of a sample
              as input and returns the transformed element.
          lazy : bool, default False
              If False, transforms all samples at once. Otherwise,
              transforms each sample on demand. Note that if `fn`
              is stochastic, you must set lazy to True or you will
              get the same result on all epochs.
  
          Returns
          -------
          Dataset
              The transformed dataset.