B or :CUBIC</li>
        <li>a number that represents the curvature value for all the segments</li>
        <li>a list of the prior values to specify the curvature values for each segment</li>
      </ul>

      <p>
        The <code>:BASE</code> keyword is an alternative to <code>:CURVE</code>.
        If <code>BASE</code> is a number, it is the envelope's base in the style
        of the sound synthesis package CLM (Common Lisp Music), where <code>BASE</code>
        is <code>e^k</code> and the curvature 