keras-team/keras · error · ValueError

`fft_length` must equal or larger than `sequence_length`. Re

Error message

`fft_length` must equal or larger than `sequence_length`. Received: sequence_length={sequence_length}, fft_length={fft_length}

What it means

Error "`fft_length` must equal or larger than `sequence_length`. Received: sequence_length={sequence_length}, fft_length={fft_length}" thrown in keras-team/keras.

Source

Thrown at keras/src/backend/numpy/math.py:206

def irfft(x, fft_length=None):
    complex_input = _get_complex_tensor_from_tuple(x)
    # numpy always outputs float64, so we need to recast the dtype
    return np.fft.irfft(
        complex_input, n=fft_length, axis=-1, norm="backward"
    ).astype(x[0].dtype)


def stft(
    x, sequence_length, sequence_stride, fft_length, window="hann", center=True
):
    if standardize_dtype(x.dtype) not in {"float32", "float64"}:
        raise TypeError(
            "Invalid input type. Expected `float32` or `float64`. "
            f"Received: input type={x.dtype}"
        )
    if fft_length < sequence_length:
        raise ValueError(
            "`fft_length` must equal or larger than `sequence_length`. "
            f"Received: sequence_length={sequence_length}, "
            f"fft_length={fft_length}"
        )
    if isinstance(window, str):
        if window not in {"hann", "hamming"}:
            raise ValueError(
                "If a string is passed to `window`, it must be one of "
                f'`"hann"`, `"hamming"`. Received: window={window}'
            )
    x = convert_to_tensor(x)
    ori_dtype = x.dtype

    if center:
        pad_width = [(0, 0) for _ in range(len(x.shape))]
        pad_width[-1] = (fft_length // 2, fft_length // 2)
        x = np.pad(x, pad_width, mode="reflect")

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/backend/numpy/math.py:206 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of keras-team/keras@7a34a03db6 (2026-08-25). Data as JSON: /api/errors/be0977472e655d68. Report an issue: GitHub.