 close to impulse
  when ignoring phase rotations.</p>
  <p>When <code>Blur</code> is 1, lowpass filter is bypassed.</p>
  <p>TODO 図</p>
  </dd>
  <dt>OT Amp., Rot. [rad/pi]</dt>
  <dd>
  <p>Amplitude and phase rotation to add source spectrum as
  overtone.</p>
  <ul>
  <li><code>OT Amp.</code> : Overtone amplitude.</li>
  <li><code>Rot. \[rad/pi\]</code> : Overtone phase rotation.</li>
  </ul>
  <p>Following shows the procedure to make final spectrum using
  <code>OT Amp.</code> and <code>Rot.</code></p>