def fft_bin_to_hz(n_bin, sample_rate_hz, fft_size):
    """Convert FFT bin index to frequency in Hz.

    Args:
        n_bin (int or float): The FFT bin index.
        sample_rate_hz (int or float): The sample rate in Hz.
        fft_size (int or float): The FFT size.

    Returns:
        The value in Hz.
    """
    n_bin = float(n_bin)
    sample_rate_hz = float(sample_rate_hz)
    fft_size = float(fft_size)
    return n_bin*sample_rate_hz/(2.0*fft_size)