Fix inconsistency between amp_to_db and db_to_amp

hopefully helps #43

Author: r9y9

audio.py

@@ -76,11 +76,11 @@ def _build_mel_basis():
 
 
 def _amp_to_db(x):
-    return 20 * np.log10(np.maximum(1e-5, x + 0.01))
+    return 20 * np.log10(x + 0.01)
 
 
 def _db_to_amp(x):
-    return np.power(10.0, x * 0.05)
+    return np.maximum(np.power(10.0, x * 0.05) - 0.01, 0.0)
 
 
 def _normalize(S):

tests/test_audio.py

@@ -0,0 +1,20 @@
+# coding: utf-8
+from __future__ import with_statement, print_function, absolute_import
+
+import sys
+from os.path import dirname, join
+sys.path.insert(0, join(dirname(__file__), ".."))
+
+import numpy as np
+from nose.plugins.attrib import attr
+
+import logging
+logging.getLogger('tensorflow').disabled = True
+
+
+@attr("local_only")
+def test_amp_to_db():
+    import audio
+    x = np.random.rand(10)
+    x_hat = audio._db_to_amp(audio._amp_to_db(x))
+    assert np.allclose(x, x_hat)