Module julius.bands

Decomposition of a signal over frequency bands in the waveform domain.

Functions

def split_bands(signal: torch.Tensor, sample_rate: float, n_bands: Optional[int] = None, cutoffs: Optional[Sequence[float]] = None, pad: bool = True, zeros: float = 8, fft: Optional[bool] = None)

Functional version of SplitBands, refer to this class for more information.

>>> x = torch.randn(6, 4, 1024)
>>> list(split_bands(x, sample_rate=64, cutoffs=[12, 24]).shape)
[3, 6, 4, 1024]

Classes

class SplitBands (sample_rate: float, n_bands: Optional[int] = None, cutoffs: Optional[Sequence[float]] = None, pad: bool = True, zeros: float = 8, fft: Optional[bool] = None)

Decomposes a signal over the given frequency bands in the waveform domain using a cascade of low pass filters as implemented by LowPassFilters. You can either specify explicitely the frequency cutoffs, or just the number of bands, in which case the frequency cutoffs will be spread out evenly in mel scale.

Args

sample_rate : float

Sample rate of the input signal in Hz.

n_bands : int or None

number of bands, when not giving them explictely with cutoffs. In that case, the cutoff frequencies will be evenly spaced in mel-space.

cutoffs : list[float] or None

list of frequency cutoffs in Hz.

pad : bool

if True, appropriately pad the input with zero over the edge. If stride=1, the output will have the same length as the input.

zeros : float

Number of zero crossings to keep. See LowPassFilters for more informations.

fft : bool or None

See LowPassFilters for more info.

Note

The sum of all the bands will always be the input signal.

Warning

Unlike LowPassFilters, the cutoffs frequencies must be provided in Hz along with the sample rate.

Shape

• Input: [*, T]
• Output: [B, *, T'], with T'=T if pad is True. If n_bands was provided, B = n_bands otherwise B = len(cutoffs) + 1

>>> bands = SplitBands(sample_rate=128, n_bands=10)
>>> x = torch.randn(6, 4, 1024)
>>> list(bands(x).shape)
[10, 6, 4, 1024]

Initialize internal Module state, shared by both nn.Module and ScriptModule.

Expand source code Browse git

class SplitBands(torch.nn.Module):
    """
    Decomposes a signal over the given frequency bands in the waveform domain using
    a cascade of low pass filters as implemented by `julius.lowpass.LowPassFilters`.
    You can either specify explicitely the frequency cutoffs, or just the number of bands,
    in which case the frequency cutoffs will be spread out evenly in mel scale.

    Args:
        sample_rate (float): Sample rate of the input signal in Hz.
        n_bands (int or None): number of bands, when not giving them explictely with `cutoffs`.
            In that case, the cutoff frequencies will be evenly spaced in mel-space.
        cutoffs (list[float] or None): list of frequency cutoffs in Hz.
        pad (bool): if True, appropriately pad the input with zero over the edge. If `stride=1`,
            the output will have the same length as the input.
        zeros (float): Number of zero crossings to keep. See `LowPassFilters` for more informations.
        fft (bool or None): See `LowPassFilters` for more info.

    ..note::
        The sum of all the bands will always be the input signal.

    ..warning::
        Unlike `julius.lowpass.LowPassFilters`, the cutoffs frequencies must be provided in Hz along
        with the sample rate.

    Shape:

        - Input: `[*, T]`
        - Output: `[B, *, T']`, with `T'=T` if `pad` is True.
            If `n_bands` was provided, `B = n_bands` otherwise `B = len(cutoffs) + 1`

    >>> bands = SplitBands(sample_rate=128, n_bands=10)
    >>> x = torch.randn(6, 4, 1024)
    >>> list(bands(x).shape)
    [10, 6, 4, 1024]
    """

    def __init__(self, sample_rate: float, n_bands: Optional[int] = None,
                 cutoffs: Optional[Sequence[float]] = None, pad: bool = True,
                 zeros: float = 8, fft: Optional[bool] = None):
        super().__init__()
        if (cutoffs is None) + (n_bands is None) != 1:
            raise ValueError("You must provide either n_bands, or cutoffs, but not boths.")

        self.sample_rate = sample_rate
        self.n_bands = n_bands
        self._cutoffs = list(cutoffs) if cutoffs is not None else None
        self.pad = pad
        self.zeros = zeros
        self.fft = fft

        if cutoffs is None:
            if n_bands is None:
                raise ValueError("You must provide one of n_bands or cutoffs.")
            if not n_bands >= 1:
                raise ValueError(f"n_bands must be greater than one (got {n_bands})")
            cutoffs = mel_frequencies(n_bands + 1, 0, sample_rate / 2)[1:-1]
        else:
            if max(cutoffs) > 0.5 * sample_rate:
                raise ValueError("A cutoff above sample_rate/2 does not make sense.")
        if len(cutoffs) > 0:
            self.lowpass = LowPassFilters(
                [c / sample_rate for c in cutoffs], pad=pad, zeros=zeros, fft=fft)
        else:
            # Here I cannot make both TorchScript and MyPy happy.
            # I miss the good old times, before all this madness was created.
            self.lowpass = None  # type: ignore

    def forward(self, input):
        if self.lowpass is None:
            return input[None]
        lows = self.lowpass(input)
        low = lows[0]
        bands = [low]
        for low_and_band in lows[1:]:
            # Get a bandpass filter by substracting lowpasses
            band = low_and_band - low
            bands.append(band)
            low = low_and_band
        # Last band is whatever is left in the signal
        bands.append(input - low)
        return torch.stack(bands)

    @property
    def cutoffs(self):
        if self._cutoffs is not None:
            return self._cutoffs
        elif self.lowpass is not None:
            return [c * self.sample_rate for c in self.lowpass.cutoffs]
        else:
            return []

    def __repr__(self):
        return simple_repr(self, overrides={"cutoffs": self._cutoffs})

Ancestors

• torch.nn.modules.module.Module

Class variables

var call_super_init : bool

var dump_patches : bool

var training : bool

Instance variables

prop cutoffs

Expand source code

@property
def cutoffs(self):
    if self._cutoffs is not None:
        return self._cutoffs
    elif self.lowpass is not None:
        return [c * self.sample_rate for c in self.lowpass.cutoffs]
    else:
        return []

Methods

def forward(self, input) ‑> Callable[..., Any]

Define the computation performed at every call.

Should be overridden by all subclasses.

Note

Although the recipe for forward pass needs to be defined within this function, one should call the :class:Module instance afterwards instead of this since the former takes care of running the registered hooks while the latter silently ignores them.