diff --git a/README.md b/README.md
index 0cdb203d..2912ff31 100644
--- a/README.md
+++ b/README.md
@@ -51,13 +51,13 @@ python compute_mean_std.py --help
 For GPU Training:
 
 ```
-CUDA_VISIBLE_DEVICES=0,1,2,3 python train.py --trainer_count 4
+CUDA_VISIBLE_DEVICES=0,1,2,3,4,5,6,7 python train.py
 ```
 
 For CPU Training:
 
 ```
-python train.py --trainer_count 8 --use_gpu False
+python train.py --use_gpu False
 ```
 
 More help for arguments:
diff --git a/data_utils/audio.py b/data_utils/audio.py
index 5d02feb6..d55fae1e 100644
--- a/data_utils/audio.py
+++ b/data_utils/audio.py
@@ -66,6 +66,54 @@ class AudioSegment(object):
         samples, sample_rate = soundfile.read(file, dtype='float32')
         return cls(samples, sample_rate)
 
+    @classmethod
+    def slice_from_file(cls, file, start=None, end=None):
+        """Loads a small section of an audio without having to load
+        the entire file into the memory which can be incredibly wasteful.
+
+        :param file: Input audio filepath or file object.
+        :type file: basestring|file
+        :param start: Start time in seconds. If start is negative, it wraps
+                      around from the end. If not provided, this function 
+                      reads from the very beginning.
+        :type start: float
+        :param end: End time in seconds. If end is negative, it wraps around
+                    from the end. If not provided, the default behvaior is
+                    to read to the end of the file.
+        :type end: float
+        :return: AudioSegment instance of the specified slice of the input
+                 audio file.
+        :rtype: AudioSegment
+        :raise ValueError: If start or end is incorrectly set, e.g. out of
+                           bounds in time.
+        """
+        sndfile = soundfile.SoundFile(file)
+        sample_rate = sndfile.samplerate
+        duration = float(len(sndfile)) / sample_rate
+        start = 0. if start is None else start
+        end = 0. if end is None else end
+        if start < 0.0:
+            start += duration
+        if end < 0.0:
+            end += duration
+        if start < 0.0:
+            raise ValueError("The slice start position (%f s) is out of "
+                             "bounds." % start)
+        if end < 0.0:
+            raise ValueError("The slice end position (%f s) is out of bounds." %
+                             end)
+        if start > end:
+            raise ValueError("The slice start position (%f s) is later than "
+                             "the slice end position (%f s)." % (start, end))
+        if end > duration:
+            raise ValueError("The slice end position (%f s) is out of bounds "
+                             "(> %f s)" % (end, duration))
+        start_frame = int(start * sample_rate)
+        end_frame = int(end * sample_rate)
+        sndfile.seek(start_frame)
+        data = sndfile.read(frames=end_frame - start_frame, dtype='float32')
+        return cls(data, sample_rate)
+
     @classmethod
     def from_bytes(cls, bytes):
         """Create audio segment from a byte string containing audio samples.
@@ -105,6 +153,20 @@ class AudioSegment(object):
         samples = np.concatenate([seg.samples for seg in segments])
         return cls(samples, sample_rate)
 
+    @classmethod
+    def make_silence(cls, duration, sample_rate):
+        """Creates a silent audio segment of the given duration and sample rate.
+
+        :param duration: Length of silence in seconds.
+        :type duration: float
+        :param sample_rate: Sample rate.
+        :type sample_rate: float
+        :return: Silent AudioSegment instance of the given duration.
+        :rtype: AudioSegment
+        """
+        samples = np.zeros(int(duration * sample_rate))
+        return cls(samples, sample_rate)
+
     def to_wav_file(self, filepath, dtype='float32'):
         """Save audio segment to disk as wav file.
         
@@ -130,68 +192,6 @@ class AudioSegment(object):
             format='WAV',
             subtype=subtype_map[dtype])
 
-    @classmethod
-    def slice_from_file(cls, file, start=None, end=None):
-        """Loads a small section of an audio without having to load
-        the entire file into the memory which can be incredibly wasteful.
-
-        :param file: Input audio filepath or file object.
-        :type file: basestring|file
-        :param start: Start time in seconds. If start is negative, it wraps
-                      around from the end. If not provided, this function 
-                      reads from the very beginning.
-        :type start: float
-        :param end: End time in seconds. If end is negative, it wraps around
-                    from the end. If not provided, the default behvaior is
-                    to read to the end of the file.
-        :type end: float
-        :return: AudioSegment instance of the specified slice of the input
-                 audio file.
-        :rtype: AudioSegment
-        :raise ValueError: If start or end is incorrectly set, e.g. out of
-                           bounds in time.
-        """
-        sndfile = soundfile.SoundFile(file)
-        sample_rate = sndfile.samplerate
-        duration = float(len(sndfile)) / sample_rate
-        start = 0. if start is None else start
-        end = 0. if end is None else end
-        if start < 0.0:
-            start += duration
-        if end < 0.0:
-            end += duration
-        if start < 0.0:
-            raise ValueError("The slice start position (%f s) is out of "
-                             "bounds." % start)
-        if end < 0.0:
-            raise ValueError("The slice end position (%f s) is out of bounds." %
-                             end)
-        if start > end:
-            raise ValueError("The slice start position (%f s) is later than "
-                             "the slice end position (%f s)." % (start, end))
-        if end > duration:
-            raise ValueError("The slice end position (%f s) is out of bounds "
-                             "(> %f s)" % (end, duration))
-        start_frame = int(start * sample_rate)
-        end_frame = int(end * sample_rate)
-        sndfile.seek(start_frame)
-        data = sndfile.read(frames=end_frame - start_frame, dtype='float32')
-        return cls(data, sample_rate)
-
-    @classmethod
-    def make_silence(cls, duration, sample_rate):
-        """Creates a silent audio segment of the given duration and sample rate.
-
-        :param duration: Length of silence in seconds.
-        :type duration: float
-        :param sample_rate: Sample rate.
-        :type sample_rate: float
-        :return: Silent AudioSegment instance of the given duration.
-        :rtype: AudioSegment
-        """
-        samples = np.zeros(int(duration * sample_rate))
-        return cls(samples, sample_rate)
-
     def superimpose(self, other):
         """Add samples from another segment to those of this segment
         (sample-wise addition, not segment concatenation).
@@ -225,7 +225,7 @@ class AudioSegment(object):
         samples = self._convert_samples_from_float32(self._samples, dtype)
         return samples.tostring()
 
-    def apply_gain(self, gain):
+    def gain_db(self, gain):
         """Apply gain in decibels to samples.
 
         Note that this is an in-place transformation.
@@ -278,7 +278,7 @@ class AudioSegment(object):
                 "Unable to normalize segment to %f dB because the "
                 "the probable gain have exceeds max_gain_db (%f dB)" %
                 (target_db, max_gain_db))
-        self.apply_gain(min(max_gain_db, target_db - self.rms_db))
+        self.gain_db(min(max_gain_db, target_db - self.rms_db))
 
     def normalize_online_bayesian(self,
                                   target_db,
@@ -319,7 +319,7 @@ class AudioSegment(object):
         rms_estimate_db = 10 * np.log10(mean_squared_estimate)
         # Compute required time-varying gain.
         gain_db = target_db - rms_estimate_db
-        self.apply_gain(gain_db)
+        self.gain_db(gain_db)
 
     def resample(self, target_sample_rate, quality='sinc_medium'):
         """Resample the audio to a target sample rate.
@@ -366,6 +366,31 @@ class AudioSegment(object):
             raise ValueError("Unknown value for the sides %s" % sides)
         self._samples = padded._samples
 
+    def shift(self, shift_ms):
+        """Shift the audio in time. If `shift_ms` is positive, shift with time
+        advance; if negative, shift with time delay. Silence are padded to
+        keep the duration unchanged.
+
+        Note that this is an in-place transformation.
+
+        :param shift_ms: Shift time in millseconds. If positive, shift with
+                         time advance; if negative; shift with time delay.
+        :type shift_ms: float
+        :raises ValueError: If shift_ms is longer than audio duration.
+        """
+        if abs(shift_ms) / 1000.0 > self.duration:
+            raise ValueError("Absolute value of shift_ms should be smaller "
+                             "than audio duration.")
+        shift_samples = int(shift_ms * self._sample_rate / 1000)
+        if shift_samples > 0:
+            # time advance
+            self._samples[:-shift_samples] = self._samples[shift_samples:]
+            self._samples[-shift_samples:] = 0
+        elif shift_samples < 0:
+            # time delay
+            self._samples[-shift_samples:] = self._samples[:shift_samples]
+            self._samples[:-shift_samples] = 0
+
     def subsegment(self, start_sec=None, end_sec=None):
         """Cut the AudioSegment between given boundaries.
 
@@ -505,7 +530,7 @@ class AudioSegment(object):
         noise_gain_db = min(self.rms_db - noise.rms_db - snr_dB, max_gain_db)
         noise_new = copy.deepcopy(noise)
         noise_new.random_subsegment(self.duration, rng=rng)
-        noise_new.apply_gain(noise_gain_db)
+        noise_new.gain_db(noise_gain_db)
         self.superimpose(noise_new)
 
     @property
diff --git a/data_utils/augmentor/augmentation.py b/data_utils/augmentor/augmentation.py
index abe1a0ec..0d60bbdb 100644
--- a/data_utils/augmentor/augmentation.py
+++ b/data_utils/augmentor/augmentation.py
@@ -6,6 +6,7 @@ from __future__ import print_function
 import json
 import random
 from data_utils.augmentor.volume_perturb import VolumePerturbAugmentor
+from data_utils.augmentor.shift_perturb import ShiftPerturbAugmentor
 
 
 class AugmentationPipeline(object):
@@ -76,5 +77,7 @@ class AugmentationPipeline(object):
         """Return an augmentation model by the type name, and pass in params."""
         if augmentor_type == "volume":
             return VolumePerturbAugmentor(self._rng, **params)
+        elif augmentor_type == "shift":
+            return ShiftPerturbAugmentor(self._rng, **params)
         else:
             raise ValueError("Unknown augmentor type [%s]." % augmentor_type)
diff --git a/data_utils/augmentor/volume_perturb.py b/data_utils/augmentor/volume_perturb.py
index a5a9f6ca..62631fb0 100644
--- a/data_utils/augmentor/volume_perturb.py
+++ b/data_utils/augmentor/volume_perturb.py
@@ -36,5 +36,5 @@ class VolumePerturbAugmentor(AugmentorBase):
         :param audio_segment: Audio segment to add effects to.
         :type audio_segment: AudioSegmenet|SpeechSegment
         """
-        gain = self._rng.uniform(min_gain_dBFS, max_gain_dBFS)
+        gain = self._rng.uniform(self._min_gain_dBFS, self._max_gain_dBFS)
         audio_segment.apply_gain(gain)
diff --git a/data_utils/data.py b/data_utils/data.py
index 44af7ffa..d01ca8cc 100644
--- a/data_utils/data.py
+++ b/data_utils/data.py
@@ -45,6 +45,9 @@ class DataGenerator(object):
     :types max_freq: None|float
     :param specgram_type: Specgram feature type. Options: 'linear'.
     :type specgram_type: str
+    :param use_dB_normalization: Whether to normalize the audio to -20 dB
+                                 before extracting the features.
+    :type use_dB_normalization: bool
     :param num_threads: Number of CPU threads for processing data.
     :type num_threads: int
     :param random_seed: Random seed.
@@ -61,6 +64,7 @@ class DataGenerator(object):
                  window_ms=20.0,
                  max_freq=None,
                  specgram_type='linear',
+                 use_dB_normalization=True,
                  num_threads=multiprocessing.cpu_count(),
                  random_seed=0):
         self._max_duration = max_duration
@@ -73,7 +77,8 @@ class DataGenerator(object):
             specgram_type=specgram_type,
             stride_ms=stride_ms,
             window_ms=window_ms,
-            max_freq=max_freq)
+            max_freq=max_freq,
+            use_dB_normalization=use_dB_normalization)
         self._num_threads = num_threads
         self._rng = random.Random(random_seed)
         self._epoch = 0
diff --git a/data_utils/featurizer/audio_featurizer.py b/data_utils/featurizer/audio_featurizer.py
index 9f9d4e50..4b4d02c6 100644
--- a/data_utils/featurizer/audio_featurizer.py
+++ b/data_utils/featurizer/audio_featurizer.py
@@ -24,26 +24,64 @@ class AudioFeaturizer(object):
                      corresponding to frequencies between [0, max_freq] are
                      returned.
     :types max_freq: None|float
+    :param target_sample_rate: Audio are resampled (if upsampling or
+                               downsampling is allowed) to this before
+                               extracting spectrogram features.
+    :type target_sample_rate: float
+    :param use_dB_normalization: Whether to normalize the audio to a certain
+                                 decibels before extracting the features.
+    :type use_dB_normalization: bool
+    :param target_dB: Target audio decibels for normalization.
+    :type target_dB: float
     """
 
     def __init__(self,
                  specgram_type='linear',
                  stride_ms=10.0,
                  window_ms=20.0,
-                 max_freq=None):
+                 max_freq=None,
+                 target_sample_rate=16000,
+                 use_dB_normalization=True,
+                 target_dB=-20):
         self._specgram_type = specgram_type
         self._stride_ms = stride_ms
         self._window_ms = window_ms
         self._max_freq = max_freq
+        self._target_sample_rate = target_sample_rate
+        self._use_dB_normalization = use_dB_normalization
+        self._target_dB = target_dB
 
-    def featurize(self, audio_segment):
+    def featurize(self,
+                  audio_segment,
+                  allow_downsampling=True,
+                  allow_upsamplling=True):
         """Extract audio features from AudioSegment or SpeechSegment.
 
         :param audio_segment: Audio/speech segment to extract features from.
         :type audio_segment: AudioSegment|SpeechSegment
+        :param allow_downsampling: Whether to allow audio downsampling before
+                                   featurizing.
+        :type allow_downsampling: bool
+        :param allow_upsampling: Whether to allow audio upsampling before
+                                 featurizing.
+        :type allow_upsampling: bool
         :return: Spectrogram audio feature in 2darray.
         :rtype: ndarray
+        :raises ValueError: If audio sample rate is not supported.
         """
+        # upsampling or downsampling
+        if ((audio_segment.sample_rate > self._target_sample_rate and
+             allow_downsampling) or
+            (audio_segment.sample_rate < self._target_sample_rate and
+             allow_upsampling)):
+            audio_segment.resample(self._target_sample_rate)
+        if audio_segment.sample_rate != self._target_sample_rate:
+            raise ValueError("Audio sample rate is not supported. "
+                             "Turn allow_downsampling or allow up_sampling on.")
+        # decibel normalization
+        if self._use_dB_normalization:
+            audio_segment.normalize(target_db=self._target_dB)
+        # extract spectrogram
         return self._compute_specgram(audio_segment.samples,
                                       audio_segment.sample_rate)
 
diff --git a/data_utils/featurizer/speech_featurizer.py b/data_utils/featurizer/speech_featurizer.py
index 77020455..26283892 100644
--- a/data_utils/featurizer/speech_featurizer.py
+++ b/data_utils/featurizer/speech_featurizer.py
@@ -29,6 +29,15 @@ class SpeechFeaturizer(object):
                      corresponding to frequencies between [0, max_freq] are
                      returned.
     :types max_freq: None|float
+    :param target_sample_rate: Speech are resampled (if upsampling or
+                               downsampling is allowed) to this before
+                               extracting spectrogram features.
+    :type target_sample_rate: float
+    :param use_dB_normalization: Whether to normalize the audio to a certain
+                                 decibels before extracting the features.
+    :type use_dB_normalization: bool
+    :param target_dB: Target audio decibels for normalization.
+    :type target_dB: float
     """
 
     def __init__(self,
@@ -36,9 +45,18 @@ class SpeechFeaturizer(object):
                  specgram_type='linear',
                  stride_ms=10.0,
                  window_ms=20.0,
-                 max_freq=None):
-        self._audio_featurizer = AudioFeaturizer(specgram_type, stride_ms,
-                                                 window_ms, max_freq)
+                 max_freq=None,
+                 target_sample_rate=16000,
+                 use_dB_normalization=True,
+                 target_dB=-20):
+        self._audio_featurizer = AudioFeaturizer(
+            specgram_type=specgram_type,
+            stride_ms=stride_ms,
+            window_ms=window_ms,
+            max_freq=max_freq,
+            target_sample_rate=target_sample_rate,
+            use_dB_normalization=use_dB_normalization,
+            target_dB=target_dB)
         self._text_featurizer = TextFeaturizer(vocab_filepath)
 
     def featurize(self, speech_segment):
diff --git a/infer.py b/infer.py
index ca18569d..069b9e3e 100644
--- a/infer.py
+++ b/infer.py
@@ -58,7 +58,7 @@ parser.add_argument(
     help="Manifest path for decoding. (default: %(default)s)")
 parser.add_argument(
     "--model_filepath",
-    default='./params.tar.gz',
+    default='checkpoints/params.latest.tar.gz',
     type=str,
     help="Model filepath. (default: %(default)s)")
 parser.add_argument(
diff --git a/setup.sh b/setup.sh
index 1ae2a5ee..cdec34ff 100644
--- a/setup.sh
+++ b/setup.sh
@@ -27,4 +27,7 @@ if [ $? != 0 ]; then
     exit 1
 fi
 
+# prepare ./checkpoints
+mkdir checkpoints
+
 echo "Install all dependencies successfully."
diff --git a/train.py b/train.py
index fc23ec72..3a2d0cad 100644
--- a/train.py
+++ b/train.py
@@ -17,10 +17,10 @@ import utils
 
 parser = argparse.ArgumentParser(description=__doc__)
 parser.add_argument(
-    "--batch_size", default=32, type=int, help="Minibatch size.")
+    "--batch_size", default=256, type=int, help="Minibatch size.")
 parser.add_argument(
     "--num_passes",
-    default=20,
+    default=200,
     type=int,
     help="Training pass number. (default: %(default)s)")
 parser.add_argument(
@@ -55,7 +55,7 @@ parser.add_argument(
     help="Use sortagrad or not. (default: %(default)s)")
 parser.add_argument(
     "--max_duration",
-    default=100.0,
+    default=27.0,
     type=float,
     help="Audios with duration larger than this will be discarded. "
     "(default: %(default)s)")
@@ -67,13 +67,13 @@ parser.add_argument(
     "(default: %(default)s)")
 parser.add_argument(
     "--shuffle_method",
-    default='instance_shuffle',
+    default='batch_shuffle_clipped',
     type=str,
     help="Shuffle method: 'instance_shuffle', 'batch_shuffle', "
     "'batch_shuffle_batch'. (default: %(default)s)")
 parser.add_argument(
     "--trainer_count",
-    default=4,
+    default=8,
     type=int,
     help="Trainer number. (default: %(default)s)")
 parser.add_argument(
@@ -110,7 +110,9 @@ parser.add_argument(
     "the existing model of this path. (default: %(default)s)")
 parser.add_argument(
     "--augmentation_config",
-    default='{}',
+    default='[{"type": "shift", '
+    '"params": {"min_shift_ms": -5, "max_shift_ms": 5},'
+    '"prob": 1.0}]',
     type=str,
     help="Augmentation configuration in json-format. "
     "(default: %(default)s)")
@@ -189,7 +191,7 @@ def train():
                 print("\nPass: %d, Batch: %d, TrainCost: %f" % (
                     event.pass_id, event.batch_id + 1, cost_sum / cost_counter))
                 cost_sum, cost_counter = 0.0, 0
-                with gzip.open("params.tar.gz", 'w') as f:
+                with gzip.open("checkpoints/params.latest.tar.gz", 'w') as f:
                     parameters.to_tar(f)
             else:
                 sys.stdout.write('.')
@@ -202,6 +204,9 @@ def train():
                 reader=test_batch_reader, feeding=test_generator.feeding)
             print("\n------- Time: %d sec,  Pass: %d, ValidationCost: %s" %
                   (time.time() - start_time, event.pass_id, result.cost))
+            with gzip.open("checkpoints/params.pass-%d.tar.gz" % event.pass_id,
+                           'w') as f:
+                parameters.to_tar(f)
 
     # run train
     trainer.train(