wp_audio_shortcode not working

Okay, I’m trying to test the new wp_audio_shortcode function using the following code:

$attr = array(
		'src'      => 'http://wpthemetestdata.files.wordpress.com/2008/06/originaldixielandjazzbandwithalbernard-stlouisblues.mp3',
		'loop'     => '',
		'autoplay' => '',
		'preload' => 'none'
		);
wp_audio_shortcode( $attr )

But nothing happens. no error, nothing, just blank. I know that I’m doing something wrong but I can’t figure out what is it?