Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The RTTTL file type is primarily associated with 'Ring Tones Text Transfer Language File'. Ring Tones Text Transfer Language is a simple text-based format that you use to create ring tones that can be uploaded into your cell phone via various cell phone uploading techniques. For example, Beethoven's Fifth Symphony start could be encoded as: