def specmix(x, wv, aspl, bspl, **kwargs):
    """
    Return the mixture of aspl and bspl specified by the parameters in x.

    Parameters
    ==========
    x : tuple
        A tuple containing the model parameters as (a, b, B0, c, m)
    wv : array-like
        The wavelength of the data
    aspl, bspl : UnivariateSpline
        Spline objects that produce the acid (aspl) or base (aspl)
        molal absorption given a wavelength.
    """
    a, b, B0, c, m = x
    return a * aspl(m * wv + c) + b * bspl(m * wv + c) + B0
