$re = '/(?<=\/)(?=[^\/\n]{0,6}path)[^\/]{10}\//m';
$str = 'd:/KeepItSimple/1234path21/WAVs/filename.wav
d:/TryToKeepItSimple/5678path23/WAVs/filename2.wav
d:/Simpler/path567823/WAVs/filename2.wav
d:/TooShort/path56782/WAVs/filename2.wav
d:/TooLong/path5678234/WAVs/filename2.wav
d:/pathNotPresent/5678pat23/f3.wav
';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php