diff --git a/lib/diffext.py b/lib/diffext.py
deleted file mode 100644
index 442d755..0000000
--- a/lib/diffext.py
+++ /dev/null
@@ -1,87 +0,0 @@
-import os
-import sys
-import random
-import glob
-import soundfile as sf
-import librosa
-import numpy as np
-
-def align(file1, file2, file2_aligned, file_subtracted):
-  def get_diff(a, b):
-    corr = np.correlate(a, b, "full")
-    diff = corr.argmax() - (b.shape[0] - 1)
-    return diff
-  
-  def get_diff_val(a, b):
-    d = np.abs(a - b)
-    return np.mean(d) / max(min(np.max(d), 0.1), 1e-6)
-  
-
-  if os.path.splitext(file1)[1] == '.mp3': 
-    wav1, sr1 = librosa.load(file1, sr=None, mono=False)
-    wav2, sr2 = librosa.load(file2, sr=None, mono=False)
-    wav1 = wav1.transpose()
-    wav2 = wav2.transpose()
-  else:
-    wav1, sr1 = sf.read(file1, dtype='float32')
-    wav2, sr2 = sf.read(file2, dtype='float32')
-  assert(sr1 == sr2)
-  wav2_org = wav2.copy()
-  
-
-  counts = {}
-  for i in range(64):
-    index = int(random.uniform(44100 * 2, min(wav1.shape[0], wav2.shape[0]) - 44100 * 2))
-    shift = int(random.uniform(-22050,+22050))
-    samp1 = wav1[index      :index      +44100, 0] 
-    samp2 = wav2[index+shift:index+shift+44100, 0]
-    diff = get_diff(samp1, samp2)
-    diff -= shift
-    if abs(diff) < 22050:
-      if not diff in counts:
-        counts[diff] = 0
-      counts[diff] += 1
-  
-  max_count = 0
-  est_diff  = 0
-  for diff in counts.keys():
-    if counts[diff] > max_count:
-      max_count = counts[diff]
-      est_diff = diff
-  
-  if est_diff > 0:
-    wav2_aligned = np.append(np.zeros((est_diff, 2)), wav2_org, axis=0)
-  elif est_diff < 0:
-    wav2_aligned = wav2_org[-est_diff:]
-  elif est_diff == 0:
-    wav2_aligned = wav2_org[-est_diff:]
-  
-  min_len = min(wav1.shape[0], wav2_aligned.shape[0])
-  wav_sub = wav1[:min_len] - wav2_aligned[:min_len]
-  wav_sub = np.clip(wav_sub, -1, +1)
-  sf.write(file_subtracted, wav_sub, sr2, subtype='PCM_16')
-  
-def align_files(pat1, pat2):
-  files1 = glob.glob(pat1)
-  files2 = glob.glob(pat2)
-  files1.sort()
-  files2.sort()
-  for file1, file2 in zip(files1, files2):
-    base_name = os.path.basename(os.path.splitext(file2)[0])
-    aligned_file    = base_name + '_aligned.wav'
-    subtracted_file = base_name + '_sub.wav'
-    align(file1, file2, aligned_file, subtracted_file)
-    
-if __name__ == '__main__':
-  args = sys.argv
-  
-  if len(args) == 3:
-    align_files(args[1], args[2])
-  elif len(args) == 5:
-    align(args[1], args[2], args[3], args[4])
-  else:
-    print("align two tracks\n:" +
-          "    python align_tracks.py file-1 file-2 aligned-file-2-to-save subtracted-file-to-save" +
-          "align all track\n:" +
-          "    python align_tracks.py pattern-1 pattern-2\n" +
-          "        saved to '*_aligned.wav' and '*_sub.wav' in the current dir.")