Set up scroll events. There's also this: http://codepen.io/MikeMcChillin/pen/lDcwq which uses Ben Alman's jquery throttle.

debouncedScrollEvents.js

/**
 * scrollEvents.js 
 *
 * Licensed under the MIT license.
 * http://www.opensource.org/licenses/mit-license.php
 * 
 */
 // http://tympanus.net/codrops/2013/06/06/on-scroll-animated-header/
var scrollEvents = (function() {

	var docElem = document.documentElement,
		header = document.querySelector( '.cbp-af-header' ),
		didScroll = false,
		changeHeaderOn = 300,
		debounce = 250;


	function init() {
		window.addEventListener( 'scroll', function( event ) {
			if( !didScroll ) {
				didScroll = true;
				setTimeout( scrollPage, debounce );
			}
		}, false );
	}

	function scrollPage() {
		var sy = scrollY();
		console.log("scrollY(): " + scrollY());
		if ( sy >= changeHeaderOn ) {
			classie.add( header, 'cbp-af-header-shrink' );
		}
		else {
			classie.remove( header, 'cbp-af-header-shrink' );
		}
		didScroll = false;
	}

	// function scrollY() {
	// 	return window.pageYOffset || docElem.scrollTop;
	// }


	function scrollY(){
	    if ( typeof pageYOffset != 'undefined') {
	        //most browsers except IE before #9
	        return pageYOffset;
	    }
	    else {
	        var B = document.body; //IE 'quirks'
	        var D = document.documentElement; //IE with doctype
	        D = ( D.clientHeight ) ? D : B;
	        return D.scrollTop;
	    }
	}



	init();

})();

scroll-events.coffee

#########################
# Scroll events
#########################
$(window).scroll ->
    scroll = $(window).scrollTop()