Pass a PHP variable (loop-audio.php) to jQuery function (js/script.js)

You could use ajax to get the value from a function read about it here: http://codex.wordpress.org/AJAX_in_Plugins

you can also save the variable in the database with transients if the function runs on every load. http://codex.wordpress.org/Transients_API

then use http://codex.wordpress.org/Function_Reference/wp_localize_script to load the var to a global javascript var.

Update: This is a ugly way to do this. In your template where you want to save the var:

<script type="text/javascript">
 <?php print_var(); ?>
</script>

And in your function:

<?php
// register a global outside the function
global $myVar;
function MyFunc(){
global $myVar;
...
//save the var in the global!
$MyVar = $a;
...
}

//function
function print_var(){
global $MyVar;
 echo "var myGlobalJsVar = ". $MyVar .";";
}

?>