$re = '/\n([A-Z])/m';
$str = 'I like to start this exercise with a slow metronome and gradually raise the tempo. I use singles, doubles, and paradiddles but you can also use pretty much any other rudiment.
The idea is to play the part that one hand would normally play but with unison strokes.';
$subst = "[::jump::]$1";
$result = preg_replace($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