I am developing a small project and i need a help in JQuery Scroll event. I wrote code loading data while scrolling using following code

$(window).scroll(function(){
            if ($(window).scrollTop() > ($(document).height() - $(window).height())*.75){
                $('#loadingimage').css({"bottom":"10px", "right":"10px"}).fadeIn('fast');
                $.ajax
                ({
                    type: "POST",
                    url: "../../scroll_load.php",
                    data: "letter="+letter+"&start="+start,
                    success: function(msg)
                    {

                        $('#new_music_videos .appendvideos').append(msg).children(':last').hide().fadeIn('slow');
                        $('#loadingimage').fadeOut('fast');
                    }
                });

            }
            });

But data loading while the scroll bar is moving at bottom of the screen only. How can i make it for scroll upto 3/4 of the screen.

Thanks a Lot.