diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation.py
index 5c8126bb28..8faa4e2652 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation.py
@@ -6,21 +6,119 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+import os
+
+from . import data_access
+
 class NoiseGenerator(object):
+  """Abstract class responsible for the generation of noisy signals.
+
+  Given a clean signal, it generates two streams named noisy signal and
+  reference.  The former is the clean signal deteriorated by the noise source,
+  the latter goes trhough the same deterioration process, but more "gently".
+  Noisy signal and reference are produced so that the reference is the signal
+  expected at the output of the APM module when the latter is fed with the nosiy
+  signal.
+
+  This is useful since it is not realistic to expect that APM will remove all
+  the background noise or all the echo. Hence, the process that generates the
+  reference signal is responsible for setting realistic expectations.
+
+  Finally, note that a noise source can generate multiple input-reference pairs.
+  """
 
   NAME = None
   REGISTERED_CLASSES = {}
 
   def __init__(self):
-    pass
+    # Input
+    self._noisy_signal_filepaths = None
+    self._output_paths = None
+    self._reference_signal_filepaths = None
+    self.clear()
 
   @classmethod
   def register_class(cls, class_to_register):
-    """
-    Decorator to automatically register the classes that extend NoiseGenerator.
+    """ Decorator to automatically register the classes that extend
+        NoiseGenerator.
     """
     cls.REGISTERED_CLASSES[class_to_register.NAME] = class_to_register
 
+  @property
+  def config_names(self):
+    return self._noisy_signal_filepaths.keys()
+
+  @property
+  def noisy_signal_filepaths(self):
+    return self._noisy_signal_filepaths
+
+  @property
+  def output_paths(self):
+    return self._output_paths
+
+  @property
+  def reference_signal_filepaths(self):
+    return self._reference_signal_filepaths
+
+  def generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    self.clear()
+    return self._generate(
+        input_signal_filepath, input_noise_cache_path, base_output_path)
+
+  def clear(self):
+    self._noisy_signal_filepaths = {}
+    self._output_paths = {}
+    self._reference_signal_filepaths = {}
+
+  def _generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    raise NotImplementedError()
+
+  def _add_noise_snr_pairs(self, base_output_path, noisy_mix_filepaths,
+                           snr_value_pairs):
+    """ Add noisy-reference signal pairs.
+
+    Args:
+      base_output_path: noisy tracks base output path.
+      noisy_mix_filepaths: nested dictionary of noisy signal paths organized
+                           by noisy track name and SNR level.
+      snr_value_pairs: list of SNR pairs.
+    """
+    for noise_track_name in noisy_mix_filepaths:
+      for snr_noisy, snr_refence in snr_value_pairs:
+        config_name = '{0}_{1:d}_{2:d}_SNR'.format(
+            noise_track_name, snr_noisy, snr_refence)
+        output_path = self._make_dir(base_output_path, config_name)
+        self._add_noise_reference_files_pair(
+            config_name=config_name,
+            noisy_signal_filepath=noisy_mix_filepaths[
+                noise_track_name][snr_noisy],
+            reference_signal_filepath=noisy_mix_filepaths[
+                noise_track_name][snr_refence],
+            output_path=output_path)
+
+  def _add_noise_reference_files_pair(self, config_name, noisy_signal_filepath,
+                                      reference_signal_filepath, output_path):
+    assert config_name not in self._noisy_signal_filepaths
+    self._noisy_signal_filepaths[config_name] = os.path.abspath(
+        noisy_signal_filepath)
+    self._output_paths[config_name] = os.path.abspath(output_path)
+    self._reference_signal_filepaths[config_name] = os.path.abspath(
+        reference_signal_filepath)
+
+    # Save noisy and reference file paths.
+    data_access.Metadata.save_audio_in_ref_paths(
+        output_path=output_path,
+        audio_in_filepath=self._noisy_signal_filepaths[config_name],
+        audio_ref_filepath=self._reference_signal_filepaths[config_name])
+
+  @classmethod
+  def _make_dir(cls, base_output_path, noise_generator_config_name):
+    output_path = os.path.join(base_output_path, noise_generator_config_name)
+    data_access.make_directory(output_path)
+    return output_path
+
 
 # Identity generator.
 @NoiseGenerator.register_class
@@ -35,8 +133,19 @@ class IdentityGenerator(NoiseGenerator):
   def __init__(self):
     NoiseGenerator.__init__(self)
 
+  def _generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    CONFIG_NAME = 'default'
+    output_path = self._make_dir(base_output_path, CONFIG_NAME)
+    self._add_noise_reference_files_pair(
+        config_name=CONFIG_NAME,
+        noisy_signal_filepath=input_signal_filepath,
+        reference_signal_filepath=input_signal_filepath,
+        output_path=output_path)
 
-@NoiseGenerator.register_class
+
+# TODO(alessiob): remove comment when class implemented.
+# @NoiseGenerator.register_class
 class WhiteNoiseGenerator(NoiseGenerator):
   """
   Additive white noise generator.
@@ -47,8 +156,14 @@ class WhiteNoiseGenerator(NoiseGenerator):
   def __init__(self):
     NoiseGenerator.__init__(self)
 
+  def _generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    # TODO(alessiob): implement.
+    pass
 
-@NoiseGenerator.register_class
+
+# TODO(alessiob): remove comment when class implemented.
+# @NoiseGenerator.register_class
 class NarrowBandNoiseGenerator(NoiseGenerator):
   """
   Additive narrow-band noise generator.
@@ -59,8 +174,14 @@ class NarrowBandNoiseGenerator(NoiseGenerator):
   def __init__(self):
     NoiseGenerator.__init__(self)
 
+  def _generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    # TODO(alessiob): implement.
+    pass
 
-@NoiseGenerator.register_class
+
+# TODO(alessiob): remove comment when class implemented.
+# @NoiseGenerator.register_class
 class EnvironmentalNoiseGenerator(NoiseGenerator):
   """
   Additive environmental noise generator.
@@ -71,8 +192,14 @@ class EnvironmentalNoiseGenerator(NoiseGenerator):
   def __init__(self):
     NoiseGenerator.__init__(self)
 
+  def _generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    # TODO(alessiob): implement.
+    pass
 
-@NoiseGenerator.register_class
+
+# TODO(alessiob): remove comment when class implemented.
+# @NoiseGenerator.register_class
 class EchoNoiseGenerator(NoiseGenerator):
   """
   Echo noise generator.
@@ -82,3 +209,8 @@ class EchoNoiseGenerator(NoiseGenerator):
 
   def __init__(self):
     NoiseGenerator.__init__(self)
+
+  def _generate(
+      self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    # TODO(alessiob): implement.
+    pass