Research->Ringtone->Message types for DOCOMO
This page provides information about Ringtone file format for NTT DOCOMO.
Message types
MFi contains 3 main kinds of messages.
(A) To set up files and songs
(B) To set up one of channels
(C) To make sounds with a channel
System messages and Channel messages
In message (A), selecting beginning/ending of trucks and tempo.
In message (B), setting up tone quality and laudness. Let's call both messages(A) and (B) together "System Message" since they have the same constructions as byte-row. (B) can also be called "Channel Message".

System Message consists of 3 bytes. The first byte which is second one in the whole Event contains FFh. The second byte contains its objects of setthing up, the third one contains values to be set up.
Note Messages
(C) is the message to make and play sounds actually. Let's call this "Note Message". Its fitst byte has a value for Channel and pitch, and the second one has note length(Gatetime).
Structures of Event
Event is the combination of Deltatime and Message. Each Message has Deltatime at the beginning which indicates process from the previous Message. In MFi, a quarter note is set its duration 30h(48 in decimal number) for Deltatime and Gatetime. The maximum value for both time are FFh(255), so when making a note which is 5-a quarter notes-duration, it's effective to connect 2 notes.
Addition to that, MFi can convert Time Base, for example, it converts a quarter note into some other value.