title: What method does Librosa use to calculate Delta-MFCC?
body: <p>I am trying to generate the delta-MFCCs. Apparently there are several implementations. I found the "regression" formula <a href="http://www1.icsi.berkeley.edu/Speech/docs/HTKBook/node65_mn.html" rel="nofollow noreferrer">link here</a>. But I don't understand why Librosa uses Savitsky-Golay filter, which is a smoothing filter. I have not found any blog/article which shows the use of Sav-Gol filter for delta mfcc. And, obviously, the deltas returned by the two don't match. 
  Can someone elaborate on it?</p>