;&quot;&quot;Filters a primary signal and produces a reference signal.</span>

<span class="sd">        Signals are Hilbert transformed to complex as necessary.</span>

<span class="sd">        Arguments:</span>
<span class="sd">            d: list | numpy.ndarray - primary signal.</span>

<span class="sd">        Returns:</span>
<span class="sd">            y: numpy.ndarray - reference signal.</span>
<span class="sd">            e: numpy.ndarray - error signal.</span>
<span class="sd">            b: numpy.