Source code for diffsptk.modules.c2mpir

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# Copyright 2022 SPTK Working Group                                        #
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import torch
from torch import nn

from ..misc.utils import cexp
from ..misc.utils import check_size




class CepstrumToMinimumPhaseImpulseResponse(nn.Module):
    """See `this page <https://sp-nitech.github.io/sptk/latest/main/c2mpir.html>`_
    for details.

    Parameters
    ----------
    cep_order : int >= 0
        Order of cepstrum, :math:`M`.

    ir_length : int >= 1
        Length of impulse response, :math:`N`.

    n_fft : int >> N
        Number of FFT bins. Accurate conversion requires the large value.

    """

    def __init__(self, cep_order, ir_length, n_fft=512):
        super().__init__()

        assert 0 <= cep_order
        assert 1 <= ir_length
        assert max(cep_order + 1, ir_length) <= n_fft

        self.cep_order = cep_order
        self.ir_length = ir_length
        self.n_fft = n_fft



    def forward(self, c):
        """Convert cepstrum to minimum phase impulse response.

        Parameters
        ----------
        c : Tensor [shape=(..., M+1)]
            Cepstral coefficients.

        Returns
        -------
        out : Tensor [shape=(..., N)]
            Truncated minimum phase impulse response.

        Examples
        --------
        >>> c = diffsptk.ramp(3)
        >>> c2mpir = diffsptk.CepstrumToMinimumPhaseImpulseResponse(3, 5)
        >>> h = c2mpir(c)
        >>> h
        tensor([1.0000, 1.0000, 2.5000, 5.1667, 6.0417])

        """
        check_size(c.size(-1), self.cep_order + 1, "dimension of cepstrum")
        return self._forward(c, self.ir_length, self.n_fft)


    @staticmethod
    def _forward(c, ir_length, n_fft):
        C = torch.fft.fft(c, n=n_fft)
        h = torch.fft.ifft(cexp(C))[..., :ir_length].real
        return h

    _func = _forward