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# Copyright 2022 SPTK Working Group #
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# http://www.apache.org/licenses/LICENSE-2.0 #
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import math
import torch
from torch import nn
from ..misc.utils import check_size
from .mgc2mgc import MelGeneralizedCepstrumToMelGeneralizedCepstrum
[docs]
class MelGeneralizedCepstrumToSpectrum(nn.Module):
"""See `this page <https://sp-nitech.github.io/sptk/latest/main/mgc2sp.html>`_
for details.
Parameters
----------
cep_order : int >= 0
Order of mel-cepstrum, :math:`M`.
fft_length : int >= 2
Number of FFT bins, :math:`L`.
alpha : float in (-1, 1)
Warping factor, :math:`\\alpha`.
gamma : float in [-1, 1]
Gamma, :math:`\\gamma`.
norm : bool
If True, assume normalized cepstrum.
mul : bool
If True, assume gamma-multiplied cepstrum.
n_fft : int >> L
Number of FFT bins. Accurate conversion requires the large value.
out_format : ['db', 'log-magnitude', 'magnitude', 'power', \
'cycle', 'radian', 'degree', 'complex']
Output format.
"""
def __init__(
self,
cep_order,
fft_length,
*,
alpha=0,
gamma=0,
norm=False,
mul=False,
n_fft=512,
out_format="power",
):
super().__init__()
self.cep_order = cep_order
self.mgc2c = MelGeneralizedCepstrumToMelGeneralizedCepstrum(
cep_order,
fft_length // 2,
in_alpha=alpha,
in_gamma=gamma,
in_norm=norm,
in_mul=mul,
n_fft=n_fft,
)
self.formatter = self._formatter(out_format)
[docs]
def forward(self, mc):
"""Convert mel-cepstrum to spectrum.
Parameters
----------
mc : Tensor [shape=(..., M+1)]
Mel-cepstrum.
Returns
-------
out : Tensor [shape=(..., L/2+1)]
Spectrum.
Examples
--------
>>> x = diffsptk.ramp(19)
>>> stft = diffsptk.STFT(frame_length=10, frame_period=10, fft_length=16)
>>> mcep = diffsptk.MelCepstralAnalysis(3, 16, 0.1, n_iter=1)
>>> mc = mcep(stft(x))
>>> mc
tensor([[-0.8851, 0.7917, -0.1737, 0.0175],
[-0.3522, 4.4222, -1.0882, -0.0511]])
>>> mc2sp = diffsptk.MelGeneralizedCepstrumToSpectrum(3, 8, 0.1)
>>> sp = mc2sp(mc)
>>> sp
tensor([[6.0634e-01, 4.6702e-01, 1.7489e-01, 4.4821e-02, 2.3869e-02],
[3.5677e+02, 1.9435e+02, 6.0078e-01, 2.4278e-04, 8.8537e-06]])
"""
check_size(mc.size(-1), self.cep_order + 1, "dimension of cepstrum")
return self._forward(self.mgc2c(mc), self.formatter)
@staticmethod
def _forward(c, formatter):
sp = torch.fft.rfft(c, n=(c.size(-1) - 1) * 2)
sp = formatter(sp)
return sp
@staticmethod
def _func(mc, fft_length, alpha, gamma, norm, mul, n_fft, out_format):
c = MelGeneralizedCepstrumToMelGeneralizedCepstrum._func(
mc,
fft_length // 2,
in_alpha=alpha,
in_gamma=gamma,
in_norm=norm,
in_mul=mul,
out_alpha=0,
out_gamma=0,
out_norm=False,
out_mul=False,
n_fft=n_fft,
)
formatter = MelGeneralizedCepstrumToSpectrum._formatter(out_format)
return MelGeneralizedCepstrumToSpectrum._forward(c, formatter)
@staticmethod
def _formatter(out_format):
if out_format in (0, "db"):
c = 20 / math.log(10)
return lambda x: x.real * c
elif out_format in (1, "log-magnitude"):
return lambda x: x.real
elif out_format in (2, "magnitude"):
return lambda x: torch.exp(x.real)
elif out_format in (3, "power"):
return lambda x: torch.exp(2 * x.real)
elif out_format in (4, "cycle"):
return lambda x: x.imag / torch.pi
elif out_format in (5, "radian"):
return lambda x: x.imag
elif out_format in (6, "degree"):
c = 180 / torch.pi
return lambda x: x.imag * c
elif out_format == "complex":
return lambda x: torch.polar(torch.exp(x.real), x.imag)
raise ValueError(f"out_format {out_format} is not supported.")