You can rewrite you code as
<title>
<?php if (!function_exists( 'is_product_category' )) {
if( is_product_category( 'cds' ) ) { ?>
CD
<?php } elseif ( is_product_category( 'dvds' ) ) {?>
DVD
<?php }
}else { wp_title( '|', true, 'right' ); } ?>