Changing title of wordpress RSS feed

In functions.php of theme:

add_filter( 'wp_title_rss', 'my_rss_filter', 20, 1 );

function my_rss_filter( $rss_title ) {
    $rss_title="New Title";
    return $rss_title;
}

I added a lower priority of 20, and just ditched the deprecated stuff altogether.
You could just return a text string as you have it, of course, but I included the rest for a more complete reference.