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spafe.features.mfcc#

Description : Mel and inverse Mel Features Cepstral Coefﬁcients (MFCCs and IMFCCs) extraction algorithm implementation.
Copyright (c) 2019-2023 Ayoub Malek. This source code is licensed under the terms of the BSD 3-Clause License. For a copy, see <https://github.com/SuperKogito/spafe/blob/master/LICENSE>.

spafe.features.mfcc.mel_spectrogram(sig, fs: int = 16000, pre_emph: bool = True, pre_emph_coeff: float = 0.97, window: Optional[SlidingWindow] = None, nfilts: int = 24, nfft: int = 512, low_freq: float = 0, high_freq: Optional[float] = None, scale: Literal['ascendant', 'descendant', 'constant'] = 'constant', fbanks: Optional[ndarray] = None, conversion_approach: Literal['Oshaghnessy', 'Lindsay'] = 'Oshaghnessy') → ndarray[source]#

Compute the mel scale spectrogram.

Parameters

sig (numpy.ndarray) – a mono audio signal (Nx1) from which to compute features.
fs (int) – the sampling frequency of the signal we are working with. (Default is 16000).
pre_emph (bool) – apply pre-emphasis if 1. (Default is True).
pre_emph_coeff (float) – pre-emphasis filter coefficient. (Default is 0.97).
window (SlidingWindow) – sliding window object. (Default is None).
nfilts (int) – the number of filters in the filter bank. (Default is 40).
nfft (int) – number of FFT points. (Default is 512).
low_freq (float) – lowest band edge of mel filters (Hz). (Default is 0).
high_freq (float) – highest band edge of mel filters (Hz). (Default is samplerate / 2).
scale (str) – monotonicity behavior of the filter banks. (Default is “constant”).
fbanks (numpy.ndarray) – filter bank matrix). (Default is None).
conversion_approach (str) – approach to use for conversion to the erb scale. (Default is “Oshaghnessy”).

Returns

the mel spectrogram (num_frames x nfilts). (numpy.ndarray) : the mel center frequencies.

Return type

(numpy.ndarray)

Tip

scale : can take the following options [“constant”, “ascendant”, “descendant”].
dct : can take the following options [1, 2, 3, 4].
normalize : can take the following options [“mvn”, “ms”, “vn”, “mn”].
conversion_approach : can take the following options [“Oshaghnessy”, “Beranek”, “Lindsay”]. Note that the use of different options than the default can lead to unexpected behavior/issues.

Note

../_images/mel_spectrogram.png — Architecture of Mel spectrogram extraction algorithm.#

Examples

from spafe.features.mfcc import mel_spectrogram
from spafe.utils.vis import show_spectrogram
from spafe.utils.preprocessing import SlidingWindow
from scipy.io.wavfile import read

# read audio
fpath = "../../../tests/data/test.wav"
fs, sig = read(fpath)

mSpec, _ = mel_spectrogram(sig,
                                fs=fs,
                                pre_emph=0,
                                pre_emph_coeff=0.97,
                                window=SlidingWindow(0.03, 0.015, "hamming"),
                                nfilts=128,
                                nfft=2048,
                                low_freq=0,
                                high_freq=fs/2)


show_spectrogram(mSpec.T,
                 fs,
                 xmin=0,
                 xmax=len(sig)/fs,
                 ymin=0,
                 ymax=(fs/2)/1000,
                 dbf=80.0,
                 xlabel="Time (s)",
                 ylabel="Frequency (kHz)",
                 title="Mel spectrogram (dB)",
                 cmap="jet")

spafe.features.mfcc.mfcc(sig: ndarray, fs: int = 16000, num_ceps: int = 13, pre_emph: bool = True, pre_emph_coeff: float = 0.97, window: Optional[SlidingWindow] = None, nfilts: int = 24, nfft: int = 512, low_freq: float = 0, high_freq: Optional[float] = None, scale: Literal['ascendant', 'descendant', 'constant'] = 'constant', dct_type: int = 2, use_energy=False, lifter: Optional[int] = None, normalize: Optional[Literal['mvn', 'ms', 'vn', 'mn']] = None, fbanks: Optional[ndarray] = None, conversion_approach: Literal['Oshaghnessy', 'Lindsay'] = 'Oshaghnessy') → ndarray[source]#

Compute MFCC features (Mel-frequency cepstral coefficients) from an audio signal. This function offers multiple approaches to features extraction depending on the input parameters. This MFCC implemenation is using FFT and can summarized in the following:

pre-empahsis

framing + Windowing

take the absolute value of the FFT

warp to a Mel frequency scale

take the DCT of the log-Mel-spectrum

return the first <num_ceps> components

Parameters

sig (numpy.ndarray) – a mono audio signal (Nx1) from which to compute features.
fs (int) – the sampling frequency of the signal we are working with. (Default is 16000).
num_ceps (int) – number of cepstra to return. (Default is 13).
pre_emph (bool) – apply pre-emphasis if 1. (Default is True).
pre_emph_coeff (float) – pre-emphasis filter coefficient. (Default is 0.97).
window (SlidingWindow) – sliding window object. (Default is None).
nfilts (int) – the number of filters in the filter bank. (Default is 40).
nfft (int) – number of FFT points. (Default is 512).
low_freq (float) – lowest band edge of mel filters (Hz). (Default is 0).
high_freq (float) – highest band edge of mel filters (Hz). (Default is samplerate / 2).
scale (str) – monotonicity behavior of the filter banks. (Default is “constant”).
dct_type (int) – type of DCT used. (Default is 2).
use_energy (bool) – overwrite C0 with true log energy. (Default is False).
lifter (int) – apply liftering if not None. (Default is None).
normalize (str) – apply normalization if approach specified. (Default is None).
fbanks (numpy.ndarray) – filter bank matrix. (Default is None).
conversion_approach (str) – approach to use for conversion to the erb scale. (Default is “Oshaghnessy”).

Returns

features - the MFFC features: num_frames x num_ceps

Return type

(numpy.ndarray)

Tip

scale : can take the following options [“constant”, “ascendant”, “descendant”].
dct : can take the following options [1, 2, 3, 4].
normalize : can take the following options [“mvn”, “ms”, “vn”, “mn”].
conversion_approach : can take the following options [“Oshaghnessy”, “Lindsay”]. Note that the use of different options than the default can lead to unexpected behavior/issues.

Note

../_images/mfccs.png — Architecture of Mel frequency cepstral coefﬁcients extraction.#

Examples

from scipy.io.wavfile import read
from spafe.features.mfcc import mfcc
from spafe.utils.preprocessing import SlidingWindow
from spafe.utils.vis import show_features

# read audio
fpath = "../../../tests/data/test.wav"
fs, sig = read(fpath)

# compute mfccs and mfes
mfccs  = mfcc(sig,
              fs=fs,
              pre_emph=1,
              pre_emph_coeff=0.97,
              window=SlidingWindow(0.03, 0.015, "hamming"),
              nfilts=128,
              nfft=2048,
              low_freq=0,
              high_freq=8000,
              normalize="mvn")

# visualize features
show_features(mfccs, "Mel Frequency Cepstral Coefﬁcients", "MFCC Index", "Frame Index")

spafe.features.mfcc.imfcc(sig: ndarray, fs: int = 16000, num_ceps=13, pre_emph: bool = True, pre_emph_coeff: float = 0.97, window: Optional[SlidingWindow] = None, nfilts: int = 24, nfft: int = 512, low_freq: float = 0, high_freq: Optional[float] = None, scale: Literal['ascendant', 'descendant', 'constant'] = 'constant', dct_type=2, use_energy=False, lifter=0, normalize=None, fbanks: Optional[ndarray] = None, conversion_approach: Literal['Oshaghnessy', 'Lindsay'] = 'Oshaghnessy') → ndarray[source]#

Compute Inverse MFCC features from an audio signal.

Parameters

sig (numpy.ndarray) – a mono audio signal (Nx1) from which to compute features.
fs (int) – the sampling frequency of the signal we are working with. (Default is 16000).
num_ceps (int) – number of cepstra to return. (Default is 13).
pre_emph (bool) – apply pre-emphasis if 1. (Default is True).
pre_emph_coeff (float) – pre-emphasis filter coefficient. (Default is 0.97).
window (SlidingWindow) – sliding window object. (Default is None).
nfilts (int) – the number of filters in the filter bank. (Default is 40).
nfft (int) – number of FFT points. (Default is 512).
low_freq (float) – lowest band edge of mel filters (Hz). (Default is 0).
high_freq (float) – highest band edge of mel filters (Hz). (Default is samplerate / 2).
scale (str) – monotonicity behavior of the filter banks. (Default is “constant”).
dct_type (int) – type of DCT used. (Default is 2).
use_energy (bool) – overwrite C0 with true log energy. (Default is False).
lifter (int) – apply liftering if not None. (Default is None).
normalize (str) – apply normalization approach specified. (Default is None).
fbanks (numpy.ndarray) – filter bank matrix. (Default is None).
conversion_approach (str) – approach to use for conversion to the erb scale. (Default is “Oshaghnessy”).

Returns

features - the inverse MFFC features: num_frames x num_ceps

Return type

(numpy.ndarray)

Tip

scale : can take the following options [“constant”, “ascendant”, “descendant”].
dct : can take the following options [1, 2, 3, 4].
normalize : can take the following options [“mvn”, “ms”, “vn”, “mn”].
conversion_approach : can take the following options [“Oshaghnessy”, “Lindsay”]. Note that the use of different options than the default can lead to unexpected behavior/issues.

Note

../_images/imfccs.png — Architecture of inverse Mel frequency cepstral coefﬁcients extraction algorithm.#

Examples

from scipy.io.wavfile import read
from spafe.features.mfcc import imfcc
from spafe.utils.preprocessing import SlidingWindow
from spafe.utils.vis import show_features

# read audio
fpath = "../../../tests/data/test.wav"
fs, sig = read(fpath)

# compute mfccs and mfes
imfccs  = imfcc(sig,
                fs=fs,
                pre_emph=1,
                pre_emph_coeff=0.97,
                window=SlidingWindow(0.03, 0.015, "hamming"),
                nfilts=128,
                nfft=2048,
                low_freq=0,
                high_freq=8000,
                normalize="mvn")

# visualize features
show_features(imfccs, "Inverse Mel Frequency Cepstral Coefﬁcients", "IMFCC Index","Frame Index")

spafe.features.lpc

spafe.features.msrcc