public static function SpeexBandModeLookup($mode) {
    static $SpeexBandModeLookup = array();
    if (empty($SpeexBandModeLookup)) {
      $SpeexBandModeLookup[0] = 'narrow';
      $SpeexBandModeLookup[1] = 'wide';
      $SpeexBandModeLookup[2] = 'ultra-wide';
    }
    return (isset($SpeexBandModeLookup[$mode]) ? $SpeexBandModeLookup[$mode] : null);
  }