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# Copyright (c) Facebook, Inc. and its affiliates.
# All rights reserved.
#
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
# author: adefossez
import math
import torch as th
from torch.nn import functional as F
def sinc(t):
"""sinc.
:param t: the input tensor
"""
return th.where(t == 0, th.tensor(1., device=t.device, dtype=t.dtype),
th.sin(t) / t)
def kernel_upsample2(zeros=56):
"""kernel_upsample2.
"""
win = th.hann_window(4 * zeros + 1, periodic=False)
winodd = win[1::2]
t = th.linspace(-zeros + 0.5, zeros - 0.5, 2 * zeros)
t *= math.pi
kernel = (sinc(t) * winodd).view(1, 1, -1)
return kernel
def upsample2(x, zeros=56):
"""
Upsampling the input by 2 using sinc interpolation.
Smith, Julius, and Phil Gossett. "A flexible sampling-rate conversion method."
ICASSP'84. IEEE International Conference on Acoustics, Speech, and Signal Processing.
Vol. 9. IEEE, 1984.
"""
*other, time = x.shape
kernel = kernel_upsample2(zeros).to(x)
out = F.conv1d(x.view(-1, 1, time), kernel, padding=zeros)[..., 1:].view(
*other, time
)
y = th.stack([x, out], dim=-1)
return y.view(*other, -1)
def kernel_downsample2(zeros=56):
"""kernel_downsample2.
"""
win = th.hann_window(4 * zeros + 1, periodic=False)
winodd = win[1::2]
t = th.linspace(-zeros + 0.5, zeros - 0.5, 2 * zeros)
t.mul_(math.pi)
kernel = (sinc(t) * winodd).view(1, 1, -1)
return kernel
def downsample2(x, zeros=56):
"""
Downsampling the input by 2 using sinc interpolation.
Smith, Julius, and Phil Gossett. "A flexible sampling-rate conversion method."
ICASSP'84. IEEE International Conference on Acoustics, Speech, and Signal Processing.
Vol. 9. IEEE, 1984.
"""
if x.shape[-1] % 2 != 0:
x = F.pad(x, (0, 1))
xeven = x[..., ::2]
xodd = x[..., 1::2]
*other, time = xodd.shape
kernel = kernel_downsample2(zeros).to(x)
out = xeven + F.conv1d(
xodd.view(-1, 1, time), kernel, padding=zeros
)[..., :-1].view(*other, time)
return out.view(*other, -1).mul(0.5)
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