a></h2>
    <p>This is a pure R implementation of removing the irrelevant frequencies. First,
DFT is applied on the data and this result is filtered according to
<code>low_freq</code> and <code>high_freq</code>. Finally, an inverse DFT is performed on
these relevant frequencies. Both <code>low_freq</code> and <code>high_freq</code> must be
either between 0 and 1, meaning that they are frequencies of the period as
radians, or both &gt;1, indicating that both are starting and ending periods of the
cycle.</p>
