class_docstr: Add isotropic noise
class_docstr_tok: ["Add","isotropic","noise"]
code: def __init__(
      self,
      utt2noise=None,
      lower=-20,
      upper=-5,
      utt2ratio=None,
      filetype="list",
      dbunit=True,
      seed=None,
  ):
      self.utt2noise_file = utt2noise
      self.utt2ratio_file = utt2ratio
      self.filetype = filetype
      self.dbunit = dbunit
      self.lower = lower
      self.upper = upper
      self.state = numpy.random.RandomState(seed)
  
      if utt2ratio is not None:
          # Use the scheduled ratio for each utterances
          self.utt2ratio = {}
          with open(utt2noise, "r") as f:
              for line in f:
                  utt, snr = line.rstrip().split(None, 1)
                  snr = float(snr)
                  self.utt2ratio[utt] = snr
      else:
          # The ratio is given on runtime randomly
          self.utt2ratio = None
  
      if utt2noise is not None:
          self.utt2noise = {}
          if filetype == "list":
              with open(utt2noise, "r") as f:
                  for line in f:
                      utt, filename = line.rstrip().split(None, 1)
                      signal, rate = soundfile.read(
                          filename, dtype="int16"
                      )
                      # Load all files in memory
                      self.utt2noise[utt] = (signal, rate)
  
          elif filetype == "sound.hdf5":
              self.utt2noise = SoundHDF5File(utt2noise, "r")
          else:
              raise ValueError(filetype)
      else:
          self.utt2noise = None
  
      if utt2noise is not None and utt2ratio is not None:
          if set(self.utt2ratio) != set(self.utt2noise):
              raise RuntimeError(
                  "The uttids mismatch between {} and {}".format(
                      utt2ratio, utt2noise
                  )
              )
  
imports: import librosa
  import numpy
  import scipy
  import soundfile
  from espnet.utils.io_utils import SoundHDF5File
label_desc: Use image node_id 1 to create a new NoiseInjection object from inherited base classes: object with example: obj = NoiseInjection(utt2noise, lower, upper, utt2ratio, filetype, dbunit, seed)