diff --git a/codes/models/gpt_voice/gpt_asr_hf.py b/codes/models/gpt_voice/gpt_asr_hf.py
index 9b487441..41121d09 100644
--- a/codes/models/gpt_voice/gpt_asr_hf.py
+++ b/codes/models/gpt_voice/gpt_asr_hf.py
@@ -13,10 +13,10 @@ class ResBlock(nn.Module):
         super().__init__()
         self.net = nn.Sequential(
             nn.Conv1d(chan, chan, kernel_size=3, padding=1),
-            nn.BatchNorm1d(chan),
+            nn.GroupNorm(chan//8, chan),
             nn.ReLU(),
             nn.Conv1d(chan, chan, kernel_size=3, padding=1),
-            nn.BatchNorm1d(chan)
+            nn.GroupNorm(chan//8, chan)
         )
 
     def forward(self, x):
@@ -31,11 +31,13 @@ class MelEncoder(nn.Module):
                                      ResBlock(channels//4),
                                      ResBlock(channels//4),
                                      nn.Conv1d(channels//4, channels//2, kernel_size=3, stride=2, padding=1),
-                                     nn.BatchNorm1d(channels//2),
+                                     nn.GroupNorm(channels//16, channels//2),
                                      nn.ReLU(),
                                      ResBlock(channels//2),
                                      ResBlock(channels//2),
                                      nn.Conv1d(channels//2, channels, kernel_size=3, stride=2, padding=1),
+                                     nn.GroupNorm(channels//8, channels),
+                                     nn.ReLU(),
                                      ResBlock(channels),
                                      ResBlock(channels)
                                      )
@@ -48,7 +50,7 @@ class GptAsrHf(nn.Module):
     NUMBER_SYMBOLS = len(symbols)
     NUMBER_TEXT_TOKENS = NUMBER_SYMBOLS+1
 
-    def __init__(self, layers=8, model_dim=512, heads=8, max_symbols_per_phrase=200, max_mel_frames=1000):
+    def __init__(self, layers=8, model_dim=512, heads=8, max_symbols_per_phrase=200, max_mel_frames=1000, checkpointing=True):
         super().__init__()
         self.max_mel_frames = max_mel_frames // 4  # Mel frames are reduced by a factor of 4 during encoding.
         self.max_symbols_per_phrase = max_symbols_per_phrase
@@ -64,7 +66,9 @@ class GptAsrHf(nn.Module):
                                         n_ctx=seq_length,
                                         n_embd=model_dim,
                                         n_layer=layers,
-                                        n_head=heads))
+                                        n_head=heads,
+                                        gradient_checkpointing=checkpointing,
+                                        use_cache=not checkpointing))
         self.final_norm = nn.LayerNorm(model_dim)
         self.text_head = nn.Linear(model_dim, self.NUMBER_TEXT_TOKENS)
 
diff --git a/codes/trainer/injectors/spec_augment.py b/codes/trainer/injectors/spec_augment.py
new file mode 100644
index 00000000..fa03ec71
--- /dev/null
+++ b/codes/trainer/injectors/spec_augment.py
@@ -0,0 +1,65 @@
+# Original source: https://github.com/SeanNaren/deepspeech.pytorch/blob/master/deepspeech_pytorch/loader/sparse_image_warp.py
+# Removes the time_warp augmentation and only implements masking.
+
+import numpy as np
+import random
+import torchvision.utils
+
+from trainer.inject import Injector
+from utils.util import opt_get
+
+
+def spec_augment(mel_spectrogram, frequency_masking_para=27, time_masking_para=70, frequency_mask_num=1, time_mask_num=1):
+
+    v = mel_spectrogram.shape[1]
+    tau = mel_spectrogram.shape[2]
+
+    # Step 2 : Frequency masking
+    for i in range(frequency_mask_num):
+        f = np.random.uniform(low=0.0, high=frequency_masking_para)
+        f = int(f)
+        if v - f < 0:
+            continue
+        f0 = random.randint(0, v-f)
+        mel_spectrogram[:, f0:f0+f, :] = 0
+
+    # Step 3 : Time masking
+    for i in range(time_mask_num):
+        t = np.random.uniform(low=0.0, high=time_masking_para)
+        t = int(t)
+        if tau - t < 0:
+            continue
+        t0 = random.randint(0, tau-t)
+        mel_spectrogram[:, :, t0:t0+t] = 0
+
+    return mel_spectrogram
+
+class MelMaskInjector(Injector):
+    def __init__(self, opt, env):
+        super().__init__(opt, env)
+        self.freq_mask_sz = opt_get(opt, ['frequency_mask_size_high'], 27)
+        self.n_freq_masks = opt_get(opt, ['frequency_mask_count'], 1)
+        self.time_mask_sz = opt_get(opt, ['time_mask_size_high'], 5)
+        self.n_time_masks = opt_get(opt, ['time_mask_count'], 3)
+
+    def forward(self, state):
+        h = state[self.input]
+        return {self.output: spec_augment(h, self.freq_mask_sz, self.time_mask_sz, self.n_freq_masks, self.n_time_masks)}
+
+def visualization_spectrogram(spec, title):
+    # Turns spec into an image and outputs it to the filesystem.
+    spec = spec.unsqueeze(dim=1)
+    # Normalize so spectrogram is easier to view.
+    spec = (spec - spec.mean()) / spec.std()
+    spec = ((spec + 1) / 2).clip(0, 1)
+    torchvision.utils.save_image(spec, f'{title}.png')
+
+if __name__ == '__main__':
+    from data.audio.unsupervised_audio_dataset import load_audio
+    from trainer.injectors.base_injectors import MelSpectrogramInjector
+    spec_maker = MelSpectrogramInjector({'in': 'audio', 'out': 'spec'}, {})
+    a = load_audio('D:\\data\\audio\\libritts\\test-clean\\61\\70970\\61_70970_000007_000001.wav', 22050).unsqueeze(0)
+    s = spec_maker({'audio': a})['spec']
+    visualization_spectrogram(s, 'original spec')
+    saug = spec_augment(s, 50, 5, 1, 3)
+    visualization_spectrogram(saug, 'modified spec')