diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/BUILD.gn b/webrtc/modules/audio_processing/test/py_quality_assessment/BUILD.gn
index 38863ce251..383b107b7b 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/BUILD.gn
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/BUILD.gn
@@ -37,9 +37,11 @@ copy("lib") {
     "quality_assessment/audioproc_wrapper.py",
     "quality_assessment/data_access.py",
     "quality_assessment/eval_scores.py",
+    "quality_assessment/eval_scores_factory.py",
     "quality_assessment/eval_scores_unittest.py",
     "quality_assessment/evaluation.py",
     "quality_assessment/noise_generation.py",
+    "quality_assessment/noise_generation_factory.py",
     "quality_assessment/noise_generation_unittest.py",
     "quality_assessment/signal_processing.py",
     "quality_assessment/signal_processing_unittest.py",
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.py b/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.py
index ca7e2c3e93..7ba0028a8c 100755
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.py
@@ -63,6 +63,12 @@ def _instance_arguments_parser():
                             'are saved'),
                       default='output')
 
+  parser.add_argument('--polqa_path', required=True,
+                      help='path to the POLQA tool')
+
+  parser.add_argument('--air_db_path', required=True,
+                      help='path to the Aechen IR database')
+
   return parser
 
 
@@ -73,7 +79,9 @@ def main():
   parser = _instance_arguments_parser()
   args = parser.parse_args()
 
-  simulator = simulation.ApmModuleSimulator()
+  simulator = simulation.ApmModuleSimulator(
+      aechen_ir_database_path=args.air_db_path,
+      polqa_tool_path=args.polqa_path)
   simulator.run(
       config_filepaths=args.config_files,
       input_filepaths=args.input_files,
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.sh b/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.sh
index 84330d0d16..91cdce6750 100755
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.sh
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/apm_quality_assessment.sh
@@ -7,6 +7,30 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+# Path to the POLQA tool.
+if [ -z ${POLQA_PATH} ]; then  # Check if defined.
+  # Default location.
+  export POLQA_PATH='/var/opt/PolqaOem64'
+fi
+if [ -d "${POLQA_PATH}" ]; then
+  echo "POLQA found in ${POLQA_PATH}"
+else
+  echo "POLQA not found in ${POLQA_PATH}"
+  exit 1
+fi
+
+# Path to the Aechen IR database.
+if [ -z ${AECHEN_IR_DATABASE_PATH} ]; then  # Check if defined.
+  # Default location.
+  export AECHEN_IR_DATABASE_PATH='/var/opt/AIR_1_4'
+fi
+if [ -d "${AECHEN_IR_DATABASE_PATH}" ]; then
+  echo "AIR database found in ${AECHEN_IR_DATABASE_PATH}"
+else
+  echo "AIR database not found in ${AECHEN_IR_DATABASE_PATH}"
+  exit 1
+fi
+
 # Customize probing signals, noise sources and scores if needed.
 PROBING_SIGNALS=(probing_signals/*.wav)
 NOISE_SOURCES=( \
@@ -44,7 +68,9 @@ for probing_signal_filepath in "${PROBING_SIGNALS[@]}" ; do
     echo "Starting ${probing_signal_name} ${noise_source_name} "`
          `"(see ${LOG_FILE})"
     ./apm_quality_assessment.py \
-        -i ${probing_signal_filepath}\
+        --polqa_path ${POLQA_PATH}\
+        --air_db_path ${AECHEN_IR_DATABASE_PATH}\
+        -i ${probing_signal_filepath} \
         -o ${OUTPUT_PATH} \
         -n ${noise_source_name} \
         -c "${APM_CONFIGS[@]}" \
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/audioproc_wrapper.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/audioproc_wrapper.py
index ba46c579d0..843a84f14a 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/audioproc_wrapper.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/audioproc_wrapper.py
@@ -6,6 +6,9 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Class implementing a wrapper for audioproc_f.
+"""
+
 import cProfile
 import logging
 import os
@@ -13,7 +16,10 @@ import subprocess
 
 from .data_access import AudioProcConfigFile
 
+
 class AudioProcWrapper(object):
+  """Wrapper for audioproc_f.
+  """
 
   OUTPUT_FILENAME = 'output.wav'
   _AUDIOPROC_F_BIN_PATH = os.path.abspath('audioproc_f')
@@ -31,6 +37,14 @@ class AudioProcWrapper(object):
     return self._output_signal_filepath
 
   def run(self, config_filepath, input_filepath, output_path):
+    """Run audioproc_f.
+
+    Args:
+      config_filepath: path to the configuration file specifing the arguments
+                       for audioproc_f.
+      input_filepath: path to the audio track input file.
+      output_path: path of the audio track output file.
+    """
     # Init.
     self._input_signal_filepath = input_filepath
     self._output_signal_filepath = os.path.join(
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/data_access.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/data_access.py
index acbe03f9af..aeee74746c 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/data_access.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/data_access.py
@@ -6,12 +6,18 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Data access utility functions and classes.
+"""
+
 import json
 import os
 
+
 def make_directory(path):
-  """
-  Recursively make a directory without rising exceptions if it already exists.
+  """Recursively make a directory without rising exceptions if already existing.
+
+  Args:
+    path: path to the directory to be created.
   """
   if os.path.exists(path):
     return
@@ -19,8 +25,7 @@ def make_directory(path):
 
 
 class Metadata(object):
-  """
-  Data access class to save and load metadata.
+  """Data access class to save and load metadata.
   """
 
   def __init__(self):
@@ -30,8 +35,12 @@ class Metadata(object):
 
   @classmethod
   def load_audio_in_ref_paths(cls, metadata_path):
-    """
-    Metadata loader for input and reference audio track paths.
+    """Metadata loader for input and reference audio track paths.
+
+    Args:
+      metadata_path: path to the directory containing the metadata file.
+
+    Returns: pair of metadata file paths for the input and output audio tracks.
     """
     metadata_filepath = os.path.join(metadata_path, cls._AUDIO_IN_REF_FILENAME)
     with open(metadata_filepath) as f:
@@ -42,8 +51,7 @@ class Metadata(object):
   @classmethod
   def save_audio_in_ref_paths(cls, output_path, audio_in_filepath,
                               audio_ref_filepath):
-    """
-    Metadata saver for input and reference audio track paths.
+    """Metadata saver for input and reference audio track paths.
     """
     output_filepath = os.path.join(output_path, cls._AUDIO_IN_REF_FILENAME)
     with open(output_filepath, 'w') as f:
@@ -51,9 +59,9 @@ class Metadata(object):
 
 
 class AudioProcConfigFile(object):
-  """
-  Data access class to save and load audioproc_f argument lists to control
-  the APM flags.
+  """Data access to load/save audioproc_f argument lists.
+
+  The arguments stored in the config files are used to control the APM flags.
   """
 
   def __init__(self):
@@ -71,8 +79,7 @@ class AudioProcConfigFile(object):
 
 
 class ScoreFile(object):
-  """
-  Data access class to save and load float scalar scores.
+  """Data access class to save and load float scalar scores.
   """
 
   def __init__(self):
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores.py
index 6787850f23..202a3b73a1 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores.py
@@ -6,11 +6,15 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Evaluation score abstract class and implementations.
+"""
+
 import logging
 import os
 
-from .data_access import ScoreFile
-from .signal_processing import SignalProcessingUtils
+from . import data_access
+from . import signal_processing
+
 
 class EvaluationScore(object):
 
@@ -27,10 +31,12 @@ class EvaluationScore(object):
 
   @classmethod
   def register_class(cls, class_to_register):
-    """
+    """Register an EvaluationScore implementation.
+
     Decorator to automatically register the classes that extend EvaluationScore.
     """
     cls.REGISTERED_CLASSES[class_to_register.NAME] = class_to_register
+    return class_to_register
 
   @property
   def output_filepath(self):
@@ -41,28 +47,28 @@ class EvaluationScore(object):
     return self._score
 
   def set_reference_signal_filepath(self, filepath):
-    """
-    Set the path to the audio track used as reference signal.
+    """ Set the path to the audio track used as reference signal.
     """
     self._reference_signal_filepath = filepath
 
   def set_tested_signal_filepath(self, filepath):
-    """
-    Set the path to the audio track used as test signal.
+    """ Set the path to the audio track used as test signal.
     """
     self._tested_signal_filepath = filepath
 
   def _load_reference_signal(self):
     assert self._reference_signal_filepath is not None
-    self._reference_signal = SignalProcessingUtils.load_wav(
+    self._reference_signal = signal_processing.SignalProcessingUtils.load_wav(
         self._reference_signal_filepath)
 
   def _load_tested_signal(self):
     assert self._tested_signal_filepath is not None
-    self._tested_signal = SignalProcessingUtils.load_wav(
+    self._tested_signal = signal_processing.SignalProcessingUtils.load_wav(
         self._tested_signal_filepath)
 
   def run(self, output_path):
+    """Extracts the score for the set input-reference pair.
+    """
     self._output_filepath = os.path.join(output_path, 'score-{}.txt'.format(
         self.NAME))
     try:
@@ -79,16 +85,15 @@ class EvaluationScore(object):
     raise NotImplementedError()
 
   def _load_score(self):
-    return ScoreFile.load(self._output_filepath)
+    return data_access.ScoreFile.load(self._output_filepath)
 
   def _save_score(self):
-    return ScoreFile.save(self._output_filepath, self._score)
+    return data_access.ScoreFile.save(self._output_filepath, self._score)
 
 
 @EvaluationScore.register_class
 class AudioLevelScore(EvaluationScore):
-  """
-  Compute the difference between the average audio level of the tested and
+  """Compute the difference between the average audio level of the tested and
   the reference signals.
 
   Unit: dB
@@ -109,8 +114,7 @@ class AudioLevelScore(EvaluationScore):
 
 @EvaluationScore.register_class
 class PolqaScore(EvaluationScore):
-  """
-  Compute the POLQA score.
+  """Compute the POLQA score.
 
   Unit: MOS
   Ideal: 4.5
@@ -119,8 +123,9 @@ class PolqaScore(EvaluationScore):
 
   NAME = 'polqa'
 
-  def __init__(self):
+  def __init__(self, polqa_tool_path):
     EvaluationScore.__init__(self)
+    self._polqa_tool_path = polqa_tool_path
 
   def _run(self, output_path):
     # TODO(alessio): implement.
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_factory.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_factory.py
new file mode 100644
index 0000000000..b33d3f96b2
--- /dev/null
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_factory.py
@@ -0,0 +1,37 @@
+# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+"""EvaluationScore factory class.
+"""
+
+import logging
+
+from . import eval_scores
+
+
+class EvaluationScoreWorkerFactory(object):
+  """Factory class used to instantiate evaluation score workers.
+
+  It can be used by instanciating a factory, passing parameters to the
+  constructor. These parameters are used to instantiate evaluation score
+  workers.
+  """
+
+  def __init__(self, polqa_tool_path):
+    self._polqa_tool_path = polqa_tool_path
+
+  def GetInstance(self, evaluation_score_class):
+    """Creates an EvaluationScore instance given a class object.
+    """
+    logging.debug(
+        'factory producing a %s evaluation score', evaluation_score_class)
+    if evaluation_score_class == eval_scores.PolqaScore:
+      return eval_scores.PolqaScore(self._polqa_tool_path)
+    else:
+      # By default, no arguments in the constructor.
+      return evaluation_score_class()
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_unittest.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_unittest.py
index 7ac7dd3615..1abe786a50 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_unittest.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/eval_scores_unittest.py
@@ -6,10 +6,14 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Unit tests for the evaluation scores.
+"""
+
 import unittest
 
 from . import eval_scores
 
+
 class TestEvalScores(unittest.TestCase):
 
   def test_registered_classes(self):
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/evaluation.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/evaluation.py
index 78446a1e18..016690a2c4 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/evaluation.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/evaluation.py
@@ -6,8 +6,12 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Evaluator of the APM module.
+"""
+
 import logging
 
+
 class ApmModuleEvaluator(object):
 
   def __init__(self):
@@ -16,6 +20,10 @@ class ApmModuleEvaluator(object):
   @classmethod
   def run(cls, evaluation_score_workers, apm_output_filepath,
           reference_input_filepath, output_path):
+    """Runs the evaluation.
+
+    Iterates over the given evaluation score workers.
+    """
     # Init.
     scores = {}
 
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 ef1eec99aa..a6a8a0653c 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
@@ -7,25 +7,32 @@
 # be found in the AUTHORS file in the root of the source tree.
 
 """Noise generators producing pairs of signals intended to be used to test the
-   APM module. Each pair consists of a noisy and a reference signal. The former
-   is used as input for APM, and it is generated by adding noise to a signal.
-   The reference is the expected APM output when using the generated input.
+ APM module. Each pair consists of a noisy and a reference signal. The former
+ is used as input for APM, and it is generated by adding noise to a signal.
+ The reference is the expected APM output when using the generated input.
 
-   Throughout this file, the following naming convention is used:
-    - input signal: the clean signal (e.g., speech),
-    - noise signal: the noise to be summed up to the input signal (e.g., white
-      noise, Gaussian noise),
-    - noisy signal: input + noise.
-   The noise signal may or may not be a function of the clean signal. For
-   instance, white noise is independently generated, whereas reverberation is
-   obtained by convolving the input signal with an impulse response.
+ Throughout this file, the following naming convention is used:
+  - input signal: the clean signal (e.g., speech),
+  - noise signal: the noise to be summed up to the input signal (e.g., white
+    noise, Gaussian noise),
+  - noisy signal: input + noise.
+ The noise signal may or may not be a function of the clean signal. For
+ instance, white noise is independently generated, whereas reverberation is
+ obtained by convolving the input signal with an impulse response.
 """
 
 import logging
 import os
+import sys
+
+try:
+  import scipy.io
+except ImportError:
+  logging.critical('Cannot import the third-party Python package scipy')
+  sys.exit(1)
 
 from . import data_access
-from .signal_processing import SignalProcessingUtils
+from . import signal_processing
 
 class NoiseGenerator(object):
   """Abstract class responsible for the generation of noisy signals.
@@ -52,10 +59,12 @@ class NoiseGenerator(object):
 
   @classmethod
   def register_class(cls, class_to_register):
-    """ Decorator to automatically register the classes that extend
-        NoiseGenerator.
+    """Register an NoiseGenerator implementation.
+
+    Decorator to automatically register the classes that extend NoiseGenerator.
     """
     cls.REGISTERED_CLASSES[class_to_register.NAME] = class_to_register
+    return class_to_register
 
   @property
   def config_names(self):
@@ -76,8 +85,9 @@ class NoiseGenerator(object):
   def generate(
       self, input_signal_filepath, input_noise_cache_path, base_output_path):
     """Generate a set of noisy input and reference audiotrack file pairs.
-       This method initializes an empty set of pairs and calls the _generate()
-       method implemented in a concrete class.
+
+    This method initializes an empty set of pairs and calls the _generate()
+    method implemented in a concrete class.
     """
     self.clear()
     return self._generate(
@@ -96,7 +106,7 @@ class NoiseGenerator(object):
 
   def _add_noise_snr_pairs(self, base_output_path, noisy_mix_filepaths,
                            snr_value_pairs):
-    """ Add noisy-reference signal pairs.
+    """Adds noisy-reference signal pairs.
 
     Args:
       base_output_path: noisy tracks base output path.
@@ -142,9 +152,9 @@ class NoiseGenerator(object):
 # Identity generator.
 @NoiseGenerator.register_class
 class IdentityGenerator(NoiseGenerator):
-  """
-  Generator that adds no noise, therefore both the noisy and the reference
-  signals are the input signal.
+  """Generator that adds no noise.
+
+  Both the noisy and the reference signals are the input signal.
   """
 
   NAME = 'identity'
@@ -165,8 +175,7 @@ class IdentityGenerator(NoiseGenerator):
 
 @NoiseGenerator.register_class
 class WhiteNoiseGenerator(NoiseGenerator):
-  """
-  Additive white noise generator.
+  """Additive white noise generator.
   """
 
   NAME = 'white'
@@ -189,12 +198,16 @@ class WhiteNoiseGenerator(NoiseGenerator):
   def _generate(
       self, input_signal_filepath, input_noise_cache_path, base_output_path):
     # Load the input signal.
-    input_signal = SignalProcessingUtils.load_wav(input_signal_filepath)
-    input_signal = SignalProcessingUtils.normalize(input_signal)
+    input_signal = signal_processing.SignalProcessingUtils.load_wav(
+        input_signal_filepath)
+    input_signal = signal_processing.SignalProcessingUtils.normalize(
+      input_signal)
 
     # Create the noise track.
-    noise_signal = SignalProcessingUtils.generate_white_noise(input_signal)
-    noise_signal = SignalProcessingUtils.normalize(noise_signal)
+    noise_signal = signal_processing.SignalProcessingUtils.generate_white_noise(
+        input_signal)
+    noise_signal = signal_processing.SignalProcessingUtils.normalize(
+        noise_signal)
 
     # Create the noisy mixes (once for each unique SNR value).
     noisy_mix_filepaths = {}
@@ -207,11 +220,12 @@ class WhiteNoiseGenerator(NoiseGenerator):
       # Create and save if not done.
       if not os.path.exists(noisy_signal_filepath):
         # Create noisy signal.
-        noisy_signal = SignalProcessingUtils.mix_signals(
+        noisy_signal = signal_processing.SignalProcessingUtils.mix_signals(
             input_signal, noise_signal, snr)
 
         # Save.
-        SignalProcessingUtils.save_wav(noisy_signal_filepath, noisy_signal)
+        signal_processing.SignalProcessingUtils.save_wav(
+            noisy_signal_filepath, noisy_signal)
 
       # Add file to the collection of mixes.
       noisy_mix_filepaths[snr] = noisy_signal_filepath
@@ -230,8 +244,7 @@ class WhiteNoiseGenerator(NoiseGenerator):
 # TODO(alessiob): remove comment when class implemented.
 # @NoiseGenerator.register_class
 class NarrowBandNoiseGenerator(NoiseGenerator):
-  """
-  Additive narrow-band noise generator.
+  """Additive narrow-band noise generator.
   """
 
   NAME = 'narrow_band'
@@ -247,8 +260,7 @@ class NarrowBandNoiseGenerator(NoiseGenerator):
 
 @NoiseGenerator.register_class
 class EnvironmentalNoiseGenerator(NoiseGenerator):
-  """
-  Additive environmental noise generator.
+  """Additive environmental noise generator.
   """
 
   NAME = 'environmental'
@@ -258,6 +270,7 @@ class EnvironmentalNoiseGenerator(NoiseGenerator):
   _NOISE_TRACKS_PATH = os.path.join(os.getcwd(), 'noise_tracks')
 
   # TODO(alessiob): allow the user to have custom noise tracks.
+  # TODO(alessiob): exploit NoiseGeneratorFactory.GetInstance().
   _NOISE_TRACKS = [
       'city.wav'
   ]
@@ -277,12 +290,26 @@ class EnvironmentalNoiseGenerator(NoiseGenerator):
 
   def _generate(
       self, input_signal_filepath, input_noise_cache_path, base_output_path):
+    """Generate environmental noise.
+
+    For each noise track and pair of SNR values, the following 2 audio tracks
+    are created: the noisy signal and the reference signal. The former is
+    obtained by mixing the (clean) input signal to the corresponding noise
+    track enforcing the target SNR.
+
+    Args:
+      input_signal_filepath: (clean) input signal file path.
+      input_noise_cache_path: path for the cached noise track files.
+      base_output_path: base output path.
+    """
     # Init.
     snr_values = set([snr for pair in self._SNR_VALUE_PAIRS for snr in pair])
 
     # Load the input signal.
-    input_signal = SignalProcessingUtils.load_wav(input_signal_filepath)
-    input_signal = SignalProcessingUtils.normalize(input_signal)
+    input_signal = signal_processing.SignalProcessingUtils.load_wav(
+        input_signal_filepath)
+    input_signal = signal_processing.SignalProcessingUtils.normalize(
+        input_signal)
 
     noisy_mix_filepaths = {}
     for noise_track_filename in self._NOISE_TRACKS:
@@ -294,8 +321,10 @@ class EnvironmentalNoiseGenerator(NoiseGenerator):
         logging.error('cannot find the <%s> noise track', noise_track_filename)
         continue
 
-      noise_signal = SignalProcessingUtils.load_wav(noise_track_filepath)
-      noise_signal = SignalProcessingUtils.normalize(noise_signal)
+      noise_signal = signal_processing.SignalProcessingUtils.load_wav(
+          noise_track_filepath)
+      noise_signal = signal_processing.SignalProcessingUtils.normalize(
+          noise_signal)
 
       # Create the noisy mixes (once for each unique SNR value).
       noisy_mix_filepaths[noise_track_name] = {}
@@ -307,11 +336,12 @@ class EnvironmentalNoiseGenerator(NoiseGenerator):
         # Create and save if not done.
         if not os.path.exists(noisy_signal_filepath):
           # Create noisy signal.
-          noisy_signal = SignalProcessingUtils.mix_signals(
+          noisy_signal = signal_processing.SignalProcessingUtils.mix_signals(
               input_signal, noise_signal, snr)
 
           # Save.
-          SignalProcessingUtils.save_wav(noisy_signal_filepath, noisy_signal)
+          signal_processing.SignalProcessingUtils.save_wav(
+              noisy_signal_filepath, noisy_signal)
 
         # Add file to the collection of mixes.
         noisy_mix_filepaths[noise_track_name][snr] = noisy_signal_filepath
@@ -321,19 +351,128 @@ class EnvironmentalNoiseGenerator(NoiseGenerator):
         base_output_path, noisy_mix_filepaths, self._SNR_VALUE_PAIRS)
 
 
-# TODO(alessiob): remove comment when class implemented.
-# @NoiseGenerator.register_class
+@NoiseGenerator.register_class
 class EchoNoiseGenerator(NoiseGenerator):
-  """
-  Echo noise generator.
+  """Echo noise generator.
   """
 
   NAME = 'echo'
 
-  def __init__(self):
+  _IMPULSE_RESPONSES = {
+      'lecture': 'air_binaural_lecture_0_0_1.mat',  # Long echo.
+      'booth': 'air_binaural_booth_0_0_1.mat',  # Short echo.
+  }
+  _MAX_IMPULSE_RESPONSE_LENGTH = None
+
+  # Each pair indicates the clean vs. noisy and reference vs. noisy SNRs.
+  # The reference (second value of each pair) always has a lower amount of noise
+  # - i.e., the SNR is 5 dB higher.
+  _SNR_VALUE_PAIRS = [
+      [3, 8],  # Smallest noise.
+      [-3, 2],  # Largest noise.
+  ]
+
+  _NOISE_TRACK_FILENAME_TEMPLATE = '{0}.wav'
+  _NOISY_SIGNAL_FILENAME_TEMPLATE = '{0}_{1:d}_SNR.wav'
+
+  def __init__(self, aechen_ir_database_path):
     NoiseGenerator.__init__(self)
+    self._aechen_ir_database_path = aechen_ir_database_path
 
   def _generate(
       self, input_signal_filepath, input_noise_cache_path, base_output_path):
-    # TODO(alessiob): implement.
-    pass
+    """Generates echo noise.
+
+    For each impulse response, one noise track is created. For each impulse
+    response and pair of SNR values, the following 2 audio tracks are
+    created: the noisy signal and the reference signal. The former is
+    obtained by mixing the (clean) input signal to the corresponding noise
+    track enforcing the target SNR.
+
+    Args:
+      input_signal_filepath: (clean) input signal file path.
+      input_noise_cache_path: path for the cached noise track files.
+      base_output_path: base output path.
+    """
+    # Init.
+    snr_values = set([snr for pair in self._SNR_VALUE_PAIRS for snr in pair])
+
+    # Load the input signal.
+    input_signal = signal_processing.SignalProcessingUtils.load_wav(
+        input_signal_filepath)
+
+    noisy_mix_filepaths = {}
+    for impulse_response_name in self._IMPULSE_RESPONSES:
+      noise_track_filename = self._NOISE_TRACK_FILENAME_TEMPLATE.format(
+          impulse_response_name)
+      noise_track_filepath = os.path.join(
+          input_noise_cache_path, noise_track_filename)
+      noise_signal = None
+      try:
+        # Load noise track.
+        noise_signal = signal_processing.SignalProcessingUtils.load_wav(
+            noise_track_filepath)
+      except IOError:  # File not found.
+        # Generate noise track by applying the impulse response.
+        impulse_response_filepath = os.path.join(
+            self._aechen_ir_database_path,
+            self._IMPULSE_RESPONSES[impulse_response_name])
+        noise_signal = self._generate_noise_track(
+            noise_track_filepath, input_signal, impulse_response_filepath)
+      assert noise_signal is not None
+
+      # Create the noisy mixes (once for each unique SNR value).
+      noisy_mix_filepaths[impulse_response_name] = {}
+      for snr in snr_values:
+        noisy_signal_filepath = os.path.join(
+            input_noise_cache_path,
+            self._NOISY_SIGNAL_FILENAME_TEMPLATE.format(
+                impulse_response_name, snr))
+
+        # Create and save if not done.
+        if not os.path.exists(noisy_signal_filepath):
+          # Create noisy signal.
+          noisy_signal = signal_processing.SignalProcessingUtils.mix_signals(
+              input_signal, noise_signal, snr, bln_pad_shortest=True)
+
+          # Save.
+          signal_processing.SignalProcessingUtils.save_wav(
+              noisy_signal_filepath, noisy_signal)
+
+        # Add file to the collection of mixes.
+        noisy_mix_filepaths[impulse_response_name][snr] = noisy_signal_filepath
+
+    # Add all the noise-SNR pairs.
+    self._add_noise_snr_pairs(base_output_path, noisy_mix_filepaths,
+                              self._SNR_VALUE_PAIRS)
+
+  def _generate_noise_track(self, noise_track_filepath, input_signal,
+                            impulse_response_filepath):
+    """Generates noise track.
+
+    Generate a signal by convolving input_signal with the impulse response in
+    impulse_response_filepath; then save to noise_track_filepath.
+
+    Args:
+      noise_track_filepath: output file path for the noise track.
+      input_signal: (clean) input signal samples.
+      impulse_response_filepath: impulse response file path.
+    """
+    # Load impulse response.
+    data = scipy.io.loadmat(impulse_response_filepath)
+    impulse_response = data['h_air'].flatten()
+    if self._MAX_IMPULSE_RESPONSE_LENGTH is not None:
+      logging.info('truncating impulse response from %d to %d samples',
+                   len(impulse_response), self._MAX_IMPULSE_RESPONSE_LENGTH)
+      impulse_response = impulse_response[:self._MAX_IMPULSE_RESPONSE_LENGTH]
+
+    # Apply impulse response.
+    processed_signal = (
+        signal_processing.SignalProcessingUtils.apply_impulse_response(
+            input_signal, impulse_response))
+
+    # Save.
+    signal_processing.SignalProcessingUtils.save_wav(
+        noise_track_filepath, processed_signal)
+
+    return processed_signal
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_factory.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_factory.py
new file mode 100644
index 0000000000..acb9f07675
--- /dev/null
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_factory.py
@@ -0,0 +1,37 @@
+# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+"""NoiseGenerator factory class.
+"""
+
+import logging
+
+from . import noise_generation
+
+
+class NoiseGeneratorFactory(object):
+  """Factory class used to instantiate noise generator workers.
+
+     It can be used by instanciating a factory, passing parameters to the
+     constructor. These parameters are used to instantiate noise generator
+     workers.
+  """
+
+  def __init__(self, aechen_ir_database_path):
+    self._aechen_ir_database_path = aechen_ir_database_path
+
+  def GetInstance(self, noise_generator_class):
+    """Creates an NoiseGenerator instance given a class object.
+    """
+    logging.debug(
+        'factory producing a %s noise generator', noise_generator_class)
+    if noise_generator_class == noise_generation.EchoNoiseGenerator:
+      return noise_generation.EchoNoiseGenerator(self._aechen_ir_database_path)
+    else:
+      # By default, no arguments in the constructor.
+      return noise_generator_class()
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_unittest.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_unittest.py
index 55fd1fd2a8..2b750913ac 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_unittest.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/noise_generation_unittest.py
@@ -6,14 +6,19 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Unit tests for the noise_generation module.
+"""
+
 import os
 import shutil
 import tempfile
 import unittest
 
 from . import noise_generation
+from . import noise_generation_factory
 from . import signal_processing
 
+
 class TestNoiseGen(unittest.TestCase):
 
   def setUp(self):
@@ -36,6 +41,13 @@ class TestNoiseGen(unittest.TestCase):
     self.assertIsInstance(registered_classes, dict)
     self.assertGreater(len(registered_classes), 0)
 
+    # Instance noise generator factory.
+    noise_generator_factory = noise_generation_factory.NoiseGeneratorFactory(
+        aechen_ir_database_path='')
+    # TODO(alessiob): Replace with a mock of NoiseGeneratorFactory that takes
+    # no arguments in the ctor. For those generators that need parameters, it
+    # will return a mock generator (see the first comment in the next for loop).
+
     # Use a sample input file as clean input signal.
     input_signal_filepath = os.path.join(
         os.getcwd(), 'probing_signals', 'tone-880.wav')
@@ -47,9 +59,17 @@ class TestNoiseGen(unittest.TestCase):
 
     # Try each registered noise generator.
     for noise_generator_name in registered_classes:
+      # Exclude EchoNoiseGenerator.
+      # TODO(alessiob): Mock EchoNoiseGenerator, the mock should rely on
+      # hard-coded impulse responses. This requires a mock for
+      # NoiseGeneratorFactory. The latter knows whether returning the actual
+      # generator or a mock object (as in the case of EchoNoiseGenerator).
+      if noise_generator_name == 'echo':
+        continue
+
       # Instance noise generator.
-      noise_generator_class = registered_classes[noise_generator_name]
-      noise_generator = noise_generator_class()
+      noise_generator = noise_generator_factory.GetInstance(
+          registered_classes[noise_generator_name])
 
       # Generate the noisy input - reference pairs.
       noise_generator.generate(
@@ -78,8 +98,14 @@ class TestNoiseGen(unittest.TestCase):
 
   def _CheckNoiseGeneratorPairsSignalDurations(
       self, noise_generator, input_signal):
-    """Checks that the noisy input and the reference tracks are audio files
-       with duration >= to that of the input signal.
+    """Check duration of the signals generated by a noise generator.
+
+    Checks that the noisy input and the reference tracks are audio files
+    with duration equal to or greater than that of the input signal.
+
+    Args:
+      noise_generator: NoiseGenerator instance.
+      input_signal: AudioSegment instance.
     """
     input_signal_length = (
         signal_processing.SignalProcessingUtils.count_samples(input_signal))
@@ -111,6 +137,9 @@ class TestNoiseGen(unittest.TestCase):
 
   def _CheckNoiseGeneratorPairsOutputPaths(self, noise_generator):
     """Checks that the output path created by the generator exists.
+
+    Args:
+      noise_generator: NoiseGenerator instance.
     """
     # Iterate over the noisy signal - reference pairs.
     for noise_config_name in noise_generator.config_names:
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing.py
index 1dbff3d581..76b103d091 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing.py
@@ -8,11 +8,27 @@
 
 import array
 import logging
+import sys
+
+try:
+  import numpy as np
+except ImportError:
+  logging.critical('Cannot import the third-party Python package numpy')
+  sys.exit(1)
+
+try:
+  import pydub
+  import pydub.generators
+except ImportError:
+  logging.critical('Cannot import the third-party Python package pydub')
+  sys.exit(1)
+
+try:
+  import scipy.signal
+except ImportError:
+  logging.critical('Cannot import the third-party Python package scipy')
+  sys.exit(1)
 
-import numpy as np
-import pydub
-import pydub.generators
-import scipy.signal
 
 class SignalProcessingException(Exception):
   pass
@@ -25,7 +41,8 @@ class SignalProcessingUtils(object):
 
   @classmethod
   def load_wav(cls, filepath, channels=1):
-    """
+    """Load wav file.
+
     Return:
       AudioSegment instance.
     """
@@ -34,7 +51,8 @@ class SignalProcessingUtils(object):
 
   @classmethod
   def save_wav(cls, output_filepath, signal):
-    """
+    """Save wav file.
+
     Args:
       output_filepath: string, output file path.
       signal: AudioSegment instance.
@@ -43,8 +61,7 @@ class SignalProcessingUtils(object):
 
   @classmethod
   def count_samples(cls, signal):
-    """
-    Number of samples per channel.
+    """Number of samples per channel.
 
     Args:
       signal: AudioSegment instance.
@@ -56,7 +73,8 @@ class SignalProcessingUtils(object):
 
   @classmethod
   def generate_white_noise(cls, signal):
-    """
+    """Generate white noise.
+
     Generate white noise with the same duration and in the same format as a
     given signal.
 
@@ -75,6 +93,8 @@ class SignalProcessingUtils(object):
 
   @classmethod
   def apply_impulse_response(cls, signal, impulse_response):
+    """Apply an impulse response to a signal.
+    """
     # Get samples.
     assert signal.channels == 1, (
         'multiple-channel recordings not supported')
@@ -128,7 +148,8 @@ class SignalProcessingUtils(object):
   @classmethod
   def mix_signals(cls, signal, noise, target_snr=0.0,
                   bln_pad_shortest=False):
-    """
+    """Mix two signals with a target SNR.
+
     Mix two signals up to a desired SNR by scaling noise (noise).
     If the target SNR is +/- infinite, a copy of signal/noise is returned.
 
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing_unittest.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing_unittest.py
index 82b138c4a4..1765a2c515 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing_unittest.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/signal_processing_unittest.py
@@ -6,6 +6,9 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""Unit tests for the signal_processing module.
+"""
+
 import unittest
 
 import numpy as np
@@ -13,6 +16,7 @@ import pydub
 
 from . import signal_processing
 
+
 class TestSignalProcessing(unittest.TestCase):
 
   def testMixSignals(self):
diff --git a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/simulation.py b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/simulation.py
index ac20edc9d7..f7962001b3 100644
--- a/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/simulation.py
+++ b/webrtc/modules/audio_processing/test/py_quality_assessment/quality_assessment/simulation.py
@@ -6,24 +6,42 @@
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
+"""APM module simulator.
+"""
+
 import logging
 import os
 
 from . import audioproc_wrapper
 from . import data_access
 from . import eval_scores
+from . import eval_scores_factory
 from . import evaluation
 from . import noise_generation
+from . import noise_generation_factory
+
 
 class ApmModuleSimulator(object):
+  """APM module simulator class.
+  """
 
   _NOISE_GENERATOR_CLASSES = noise_generation.NoiseGenerator.REGISTERED_CLASSES
   _EVAL_SCORE_WORKER_CLASSES = eval_scores.EvaluationScore.REGISTERED_CLASSES
 
-  def __init__(self):
+  def __init__(self, aechen_ir_database_path, polqa_tool_path):
+    # Init.
     self._audioproc_wrapper = audioproc_wrapper.AudioProcWrapper()
     self._evaluator = evaluation.ApmModuleEvaluator()
 
+    # Instance factory objects.
+    self._noise_generator_factory = (
+        noise_generation_factory.NoiseGeneratorFactory(
+            aechen_ir_database_path=aechen_ir_database_path))
+    self._evaluation_score_factory = (
+        eval_scores_factory.EvaluationScoreWorkerFactory(
+            polqa_tool_path=polqa_tool_path))
+
+    # Properties for each run.
     self._base_output_path = None
     self._noise_generators = None
     self._evaluation_score_workers = None
@@ -38,12 +56,15 @@ class ApmModuleSimulator(object):
     self._base_output_path = os.path.abspath(output_dir)
 
     # Instance noise generators.
-    self._noise_generators = [
-        self._NOISE_GENERATOR_CLASSES[name]() for name in noise_generator_names]
+    self._noise_generators = [self._noise_generator_factory.GetInstance(
+        noise_generator_class=self._NOISE_GENERATOR_CLASSES[name]) for name in (
+            noise_generator_names)]
 
     # Instance evaluation score workers.
     self._evaluation_score_workers = [
-        self._EVAL_SCORE_WORKER_CLASSES[name]() for name in eval_score_names]
+        self._evaluation_score_factory.GetInstance(
+            evaluation_score_class=self._EVAL_SCORE_WORKER_CLASSES[name]) for (
+                name) in eval_score_names]
 
     # Set APM configuration file paths.
     self._config_filepaths = self._get_paths_collection(config_filepaths)