Motorola K3 ユーザーズマニュアル
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MIDI Audio Guidelines
The following are suggested guidelines to maximize sound quality while reducing the
overall file size of a MIDI Ring Tone file for use with the MOTOKRZR K3.
overall file size of a MIDI Ring Tone file for use with the MOTOKRZR K3.
Tip 1: Use MIDI’s running status feature
In the MIDI standard, a key-on or a key-off event will use, at most, three bytes each.
However, when several key events occur on the same MIDI-channel, the running status
feature can be used. In principle, running status means the first byte of a key-on event is
omitted. In addition, the key-on event having a velocity of zero is equivalent to the key-off
event. Thus, combining running status with key-on events that have zero velocity reduces
the number of bytes needed to encode all key events.
However, when several key events occur on the same MIDI-channel, the running status
feature can be used. In principle, running status means the first byte of a key-on event is
omitted. In addition, the key-on event having a velocity of zero is equivalent to the key-off
event. Thus, combining running status with key-on events that have zero velocity reduces
the number of bytes needed to encode all key events.
EXAMPLE:
Without using the running status, features, the sequence
91 2E 23 8E, 91 2B 50 8E, 81 2E 64 00, 81 2B 64 00
represents “Key 2E ON” Velocity 23 MIDI Ch 1”, “Key 2B ON Velocity 50 MIDI Ch 1”,
“Key 2E OFF Velocity 64 MIDI Ch 1”, “Key 2B OFF Velocity 64 MIDI Ch 1”. Using the
running status feature reduces the sequence to:
“Key 2E OFF Velocity 64 MIDI Ch 1”, “Key 2B OFF Velocity 64 MIDI Ch 1”. Using the
running status feature reduces the sequence to:
91 2E 23 8E, 2B 50 8E, 2E 00 00, 2B 00 00,
That is, the command byte is omitted and velocity zero is used for key off.
Tip 2: Use Standard MIDI File (SMF) type 1
The MIDI content can be stored in a Standard MIDI File (SMF) of type 0 or type 1. In a
type 0 SMF, the file format uses one header chunk with one-track chunk. In a type 1 SMF,
the format uses one header chunk with several track chunks. SMF type 2 should not be
used.
type 0 SMF, the file format uses one header chunk with one-track chunk. In a type 1 SMF,
the format uses one header chunk with several track chunks. SMF type 2 should not be
used.
In general, it is more efficient to store the MIDI data as a type 1 file. The increased
efficiency is achieved because each track contains only one MIDI channel and one
instrument (often the case). The running status feature can be applied on each individual
track, thereby reducing the track size. To reduce the size of the file even further, use one
track per used MIDI channel. That is, if a temple/conductor track exists, merge it with the
first instrument track and remove all unnecessary meta-events such as the “track name”
and “lyric” meta-events.
efficiency is achieved because each track contains only one MIDI channel and one
instrument (often the case). The running status feature can be applied on each individual
track, thereby reducing the track size. To reduce the size of the file even further, use one
track per used MIDI channel. That is, if a temple/conductor track exists, merge it with the
first instrument track and remove all unnecessary meta-events such as the “track name”
and “lyric” meta-events.
To summarize, the following measures can be taken in order to reduce the SMF:
1. Use SMF type 1 (Or verify that a type 1 file is smaller than a type 0 file and use the
smallest file).
2. Use running status.
3. One and only one instrument per track. Try not to change channels.
4. Do not change tempo in the middle of the music. That is, set the tempo once.
5. Use beat, instead of SMPTE, to set the tempo.
6. Do not use Copyright Text Fields.
7. Limit the use of continuous controller information such as pitch-bend and volume.