import math


def _spec_time_steps(duration, window_size=25, hop_size=10):
    """
    Compute the number of time steps of a spectrogram.

    Args:
        duration : Length of audio in seconds.
        window_size : Size of specgram window in milliseconds.
        hop_size : Size of steps between ffts in
            specgram in milliseconds.
    Returns:
        The number of time-steps in the
        output of the spectrogram.
    """
    duration_ms = duration * 1000
    return math.ceil((duration_ms - window_size) / hop_size)