Delete melbank.py
This commit is contained in:
not-matt
GitHub
parent
d9fcf1ec14
commit
0853caa8d9
@ -1,152 +0,0 @@
|
|||||||
"""This module implements a Mel Filter Bank.
|
|
||||||
In other words it is a filter bank with triangular shaped bands
|
|
||||||
arnged on the mel frequency scale.
|
|
||||||
An example ist shown in the following figure:
|
|
||||||
.. plot::
|
|
||||||
from pylab import plt
|
|
||||||
import melbank
|
|
||||||
f1, f2 = 1000, 8000
|
|
||||||
melmat, (melfreq, fftfreq) = melbank.compute_melmat(6, f1, f2, num_fft_bands=4097)
|
|
||||||
fig, ax = plt.subplots(figsize=(8, 3))
|
|
||||||
ax.plot(fftfreq, melmat.T)
|
|
||||||
ax.grid(True)
|
|
||||||
ax.set_ylabel('Weight')
|
|
||||||
ax.set_xlabel('Frequency / Hz')
|
|
||||||
ax.set_xlim((f1, f2))
|
|
||||||
ax2 = ax.twiny()
|
|
||||||
ax2.xaxis.set_ticks_position('top')
|
|
||||||
ax2.set_xlim((f1, f2))
|
|
||||||
ax2.xaxis.set_ticks(melbank.mel_to_hertz(melfreq))
|
|
||||||
ax2.xaxis.set_ticklabels(['{:.0f}'.format(mf) for mf in melfreq])
|
|
||||||
ax2.set_xlabel('Frequency / mel')
|
|
||||||
plt.tight_layout()
|
|
||||||
fig, ax = plt.subplots()
|
|
||||||
ax.matshow(melmat)
|
|
||||||
plt.axis('equal')
|
|
||||||
plt.axis('tight')
|
|
||||||
plt.title('Mel Matrix')
|
|
||||||
plt.tight_layout()
|
|
||||||
Functions
|
|
||||||
---------
|
|
||||||
"""
|
|
||||||
|
|
||||||
from numpy import abs, append, arange, insert, linspace, log10, round, zeros
|
|
||||||
|
|
||||||
|
|
||||||
def hertz_to_mel(freq):
|
|
||||||
"""Returns mel-frequency from linear frequency input.
|
|
||||||
Parameter
|
|
||||||
---------
|
|
||||||
freq : scalar or ndarray
|
|
||||||
Frequency value or array in Hz.
|
|
||||||
Returns
|
|
||||||
-------
|
|
||||||
mel : scalar or ndarray
|
|
||||||
Mel-frequency value or ndarray in Mel
|
|
||||||
"""
|
|
||||||
return 2595.0 * log10(1 + (freq / 700.0))
|
|
||||||
|
|
||||||
|
|
||||||
def mel_to_hertz(mel):
|
|
||||||
"""Returns frequency from mel-frequency input.
|
|
||||||
Parameter
|
|
||||||
---------
|
|
||||||
mel : scalar or ndarray
|
|
||||||
Mel-frequency value or ndarray in Mel
|
|
||||||
Returns
|
|
||||||
-------
|
|
||||||
freq : scalar or ndarray
|
|
||||||
Frequency value or array in Hz.
|
|
||||||
"""
|
|
||||||
return 700.0 * (10**(mel / 2595.0)) - 700.0
|
|
||||||
|
|
||||||
|
|
||||||
def melfrequencies_mel_filterbank(num_bands, freq_min, freq_max, num_fft_bands):
|
|
||||||
"""Returns centerfrequencies and band edges for a mel filter bank
|
|
||||||
Parameters
|
|
||||||
----------
|
|
||||||
num_bands : int
|
|
||||||
Number of mel bands.
|
|
||||||
freq_min : scalar
|
|
||||||
Minimum frequency for the first band.
|
|
||||||
freq_max : scalar
|
|
||||||
Maximum frequency for the last band.
|
|
||||||
num_fft_bands : int
|
|
||||||
Number of fft bands.
|
|
||||||
Returns
|
|
||||||
-------
|
|
||||||
center_frequencies_mel : ndarray
|
|
||||||
lower_edges_mel : ndarray
|
|
||||||
upper_edges_mel : ndarray
|
|
||||||
"""
|
|
||||||
|
|
||||||
mel_max = hertz_to_mel(freq_max)
|
|
||||||
mel_min = hertz_to_mel(freq_min)
|
|
||||||
delta_mel = abs(mel_max - mel_min) / (num_bands + 1.0)
|
|
||||||
frequencies_mel = mel_min + delta_mel * arange(0, num_bands + 2)
|
|
||||||
lower_edges_mel = frequencies_mel[:-2]
|
|
||||||
upper_edges_mel = frequencies_mel[2:]
|
|
||||||
center_frequencies_mel = frequencies_mel[1:-1]
|
|
||||||
return center_frequencies_mel, lower_edges_mel, upper_edges_mel
|
|
||||||
|
|
||||||
|
|
||||||
def compute_melmat(num_mel_bands=12, freq_min=64, freq_max=8000,
|
|
||||||
num_fft_bands=513, sample_rate=16000):
|
|
||||||
"""Returns tranformation matrix for mel spectrum.
|
|
||||||
Parameters
|
|
||||||
----------
|
|
||||||
num_mel_bands : int
|
|
||||||
Number of mel bands. Number of rows in melmat.
|
|
||||||
Default: 24
|
|
||||||
freq_min : scalar
|
|
||||||
Minimum frequency for the first band.
|
|
||||||
Default: 64
|
|
||||||
freq_max : scalar
|
|
||||||
Maximum frequency for the last band.
|
|
||||||
Default: 8000
|
|
||||||
num_fft_bands : int
|
|
||||||
Number of fft-frequenc bands. This ist NFFT/2+1 !
|
|
||||||
number of columns in melmat.
|
|
||||||
Default: 513 (this means NFFT=1024)
|
|
||||||
sample_rate : scalar
|
|
||||||
Sample rate for the signals that will be used.
|
|
||||||
Default: 44100
|
|
||||||
Returns
|
|
||||||
-------
|
|
||||||
melmat : ndarray
|
|
||||||
Transformation matrix for the mel spectrum.
|
|
||||||
Use this with fft spectra of num_fft_bands_bands length
|
|
||||||
and multiply the spectrum with the melmat
|
|
||||||
this will tranform your fft-spectrum
|
|
||||||
to a mel-spectrum.
|
|
||||||
frequencies : tuple (ndarray <num_mel_bands>, ndarray <num_fft_bands>)
|
|
||||||
Center frequencies of the mel bands, center frequencies of fft spectrum.
|
|
||||||
"""
|
|
||||||
center_frequencies_mel, lower_edges_mel, upper_edges_mel = \
|
|
||||||
melfrequencies_mel_filterbank(
|
|
||||||
num_mel_bands,
|
|
||||||
freq_min,
|
|
||||||
freq_max,
|
|
||||||
num_fft_bands
|
|
||||||
)
|
|
||||||
|
|
||||||
center_frequencies_hz = mel_to_hertz(center_frequencies_mel)
|
|
||||||
lower_edges_hz = mel_to_hertz(lower_edges_mel)
|
|
||||||
upper_edges_hz = mel_to_hertz(upper_edges_mel)
|
|
||||||
freqs = linspace(0.0, sample_rate / 2.0, num_fft_bands)
|
|
||||||
melmat = zeros((num_mel_bands, num_fft_bands))
|
|
||||||
|
|
||||||
for imelband, (center, lower, upper) in enumerate(zip(
|
|
||||||
center_frequencies_hz, lower_edges_hz, upper_edges_hz)):
|
|
||||||
|
|
||||||
left_slope = (freqs >= lower) == (freqs <= center)
|
|
||||||
melmat[imelband, left_slope] = (
|
|
||||||
(freqs[left_slope] - lower) / (center - lower)
|
|
||||||
)
|
|
||||||
|
|
||||||
right_slope = (freqs >= center) == (freqs <= upper)
|
|
||||||
melmat[imelband, right_slope] = (
|
|
||||||
(upper - freqs[right_slope]) / (upper - center)
|
|
||||||
)
|
|
||||||
|
|
||||||
return melmat, (center_frequencies_mel, freqs)
|
|
||||||
Loading…
Reference in New Issue
Block a user