> knowing how the open strings are supposed to sound
replywell that's the whole question isn't it? If you know how an open string is supposed to have, that's what people call absolute pitch?
Most people without absolute pitch have some level of "pitch memory", but it's not comprehensive or reliable. For instance, if you ask people to sing a pop song, they're significantly more likely than chance to sing it in the original key.
replyI know the Super Mario Bros. theme starts on an E, so I can identify an unknown pitch by recalling that theme and comparing using relative pitch. But that's quite a slow and unintuitive process, and it's easy to make a mistake. People with absolute pitch just hear the pitch without having to "recall" a reference note to compare to like that.