araso (아라소) and arata (아라타) are incorrect spelling of 알았어. 알았다.
By the way, if someone who is not acquainted with me or close to me say "알았다." Then I may think the person is very impolite and don't have any respect for me.
Maybe this videoclip will be a help to you.
http://www.youtube.com/watch?v=pniA-K5vt2U