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# Copyright (c) 2006 Carnegie Mellon University
#
# You may copy and modify this freely under the same terms as
# Sphinx-III
"""Compute Sphinx-III 1s_c_d_dd features.
This module provides a compute() function to compute 39-dimensional
single-stream features consisting of cepstra and their first and
second time derivatives. This is the default feature type used for
Sphinx-III continuous density acoustic models.
"""
__author__ = "David Huggins-Daines <dhuggins@cs.cmu.edu>"
__version__ = "$Revision$"
from numpy import zeros, concatenate
def compute(mfcc):
"""Compute 39-dimensional single-stream features consisting of cepstra
and their first and second time derivatives."""
r, c = mfcc.shape
# Pad the features to compute dcep, ddcep
pad = concatenate((zeros((3,c)), mfcc, zeros((3,c))))
# Now create the output array
feat = zeros((r, c*3),'d')
# cep
feat[:, 0:13] = mfcc
# dcep = mfc[2] - mfc[-2]
feat[:, 13:26] = (pad[5:-1] - pad[1:-5])
# ddcep = (mfc[3] - mfc[-1]) - (mfc[1] - mfc[-3])
feat[:, 26:] = (pad[6:] - pad[2:-4]) - (pad[4:-2] - pad[0:-6])
return feat
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