Rewritten the delta calculation in a more vectorial form

janluke · janluke · commit ce1febb1cbc9 · 2017-02-03T14:45:58.000+01:00
diff --git a/python_speech_features/base.py b/python_speech_features/base.py
@@ -179,10 +179,12 @@ def delta(feat, N):
     :param N: For each frame, calculate delta features based on preceding and following N frames
     :returns: A numpy array of size (NUMFRAMES by number of features) containing delta features. Each row holds 1 delta feature vector.
     """
+    if N < 1:
+        raise ValueError('N must be an integer >= 1')
     NUMFRAMES = len(feat)
     denominator = 2 * sum([i**2 for i in range(1, N+1)])
     delta_feat = numpy.empty_like(feat)
     padded = numpy.pad(feat, ((N, N), (0, 0)), mode='edge')   # padded version of feat
     for t in range(NUMFRAMES):
-        delta_feat[t] = numpy.sum([n * padded[N+t + n] for n in range(-N, N+1)], axis=0) / denominator
+        delta_feat[t] = numpy.dot(numpy.arange(-N, N+1), padded[t : t+2*N+1]) / denominator   # [t : t+2*N+1] == [(N+t)-N : (N+t)+N+1]
     return delta_feat
