convert M4A to AAC without quality loss

The iTunes's default always converts music to a M4A file, does any body know other way in converting the M4A format to the AAC format without loss of quality?

Despite trying some softwares but I have been unsatisfied about them. Converted files did not preserve origin files' quality although they were both used AAC codec.

Did Apple have any tool to help me? Infact, I like AAC codec contained in the AAC format (not in the M4A format) because it is easy to play by my portable device.