keras-team/keras · error · ValueError

`fft_length` should be not less than `frame_length`. Receive

Error message

`fft_length` should be not less than `frame_length`. Received fft_length={fft_length}, frame_length={frame_length}

What it means

Error "`fft_length` should be not less than `frame_length`. Received fft_length={fft_length}, frame_length={frame_length}" thrown in keras-team/keras.

Source

Thrown at keras/src/layers/preprocessing/stft_spectrogram.py:158

        window="hann",
        periodic=False,
        scaling="density",
        padding="valid",
        expand_dims=False,
        data_format=None,
        **kwargs,
    ):
        if frame_step is not None and (
            frame_step > frame_length or frame_step < 1
        ):
            raise ValueError(
                "`frame_step` should be a positive integer not greater than "
                f"`frame_length`. Received frame_step={frame_step}, "
                f"frame_length={frame_length}"
            )

        if fft_length is not None and fft_length < frame_length:
            raise ValueError(
                "`fft_length` should be not less than `frame_length`. "
                f"Received fft_length={fft_length}, frame_length={frame_length}"
            )

        if fft_length is not None and (fft_length & -fft_length) != fft_length:
            warnings.warn(
                "`fft_length` is recommended to be a power of two. "
                f"Received fft_length={fft_length}"
            )

        all_modes = ["log", "magnitude", "psd", "real", "imag", "angle", "stft"]

        if mode not in all_modes:
            raise ValueError(
                "Output mode is invalid, it must be one of "
                f"{', '.join(all_modes)}. Received: mode={mode}"
            )

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/layers/preprocessing/stft_spectrogram.py:158 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/745654a7b22fd8e0. Report an issue: GitHub.