MIDI Implementation
12
4. Supplementary Material
■
■ ■■
Decimal and Hexadecimal Table
In MIDI documentation, data values and addresses/sizes of exclusive messages etc. are
expressed as hexadecimal values for each 7 bits.
The following table shows how these correspond to decimal numbers.
* Hexadecimal numbers are indicated by ‘H.’
+------+------++------+------++------+------++------+------+
| D | H || D | H || D | H || D | H |
+------+------++------+------++------+------++------+------+
| 0 | 00H || 32 | 20H || 64 | 40H || 96 | 60H |
| 1 | 01H || 33 | 21H || 65 | 41H || 97 | 61H |
| 2 | 02H || 34 | 22H || 66 | 42H || 98 | 62H |
| 3 | 03H || 35 | 23H || 67 | 43H || 99 | 63H |
| 4 | 04H || 36 | 24H || 68 | 44H || 100 | 64H |
| 5 | 05H || 37 | 25H || 69 | 45H || 101 | 65H |
| 6 | 06H || 38 | 26H || 70 | 46H || 102 | 66H |
| 7 | 07H || 39 | 27H || 71 | 47H || 103 | 67H |
| 8 | 08H || 40 | 28H || 72 | 48H || 104 | 68H |
| 9 | 09H || 41 | 29H || 73 | 49H || 105 | 69H |
| 10 | 0AH || 42 | 2AH || 74 | 4AH || 106 | 6AH |
| 11 | 0BH || 43 | 2BH || 75 | 4BH || 107 | 6BH |
| 12 | 0CH || 44 | 2CH || 76 | 4CH || 108 | 6CH |
| 13 | 0DH || 45 | 2DH || 77 | 4DH || 109 | 6DH |
| 14 | 0EH || 46 | 2EH || 78 | 4EH || 110 | 6EH |
| 15 | 0FH || 47 | 2FH || 79 | 4FH || 111 | 6FH |
| 16 | 10H || 48 | 30H || 80 | 50H || 112 | 70H |
| 17 | 11H || 49 | 31H || 81 | 51H || 113 | 71H |
| 18 | 12H || 50 | 32H || 82 | 52H || 114 | 72H |
| 19 | 13H || 51 | 33H || 83 | 53H || 115 | 73H |
| 20 | 14H || 52 | 34H || 84 | 54H || 116 | 74H |
| 21 | 15H || 53 | 35H || 85 | 55H || 117 | 75H |
| 22 | 16H || 54 | 36H || 86 | 56H || 118 | 76H |
| 23 | 17H || 55 | 37H || 87 | 57H || 119 | 77H |
| 24 | 18H || 56 | 38H || 88 | 58H || 120 | 78H |
| 25 | 19H || 57 | 39H || 89 | 59H || 121 | 79H |
| 26 | 1AH || 58 | 3AH || 90 | 5AH || 122 | 7AH |
| 27 | 1BH || 59 | 3BH || 91 | 5BH || 123 | 7BH |
| 28 | 1CH || 60 | 3CH || 92 | 5CH || 124 | 7CH |
| 29 | 1DH || 61 | 3DH || 93 | 5DH || 125 | 7DH |
| 30 | 1EH || 62 | 3EH || 94 | 5EH || 126 | 7EH |
| 31 | 1FH || 63 | 3FH || 95 | 5FH || 127 | 7FH |
+------+------++------+------++------+------++------+------+
D: decimal
H: hexadecimal
* Decimal values such as MIDI channel, Bank Select, and Program Change are listed as
one(1) greater than the values given in the above table.
* A 7-bit byte can express data in the range of 128 steps. For data where greater
precision is required, we must use two or more bytes. For example, two hexadecimal
numbers aa bbH expressing two 7-bit bytes would indicate a value of aa x 128 + bb.
* In the case of values which have a ± sign, 00H = -64, 40H = ± 0, and 7FH = +63, so
that the decimal expression would be 64 less than the value given in the above
chart. In the case of two types, 00 00H = -8192, 40 00H = ± 0, and 7F 7FH = +8191.
For example if aa bbH were expressed as decimal, this would be aa bbH - 40 00H =
aa x 128 + bb - 64 x 128.
■
❍
<Example 1> What is the decimal expression of 5AH?
From the preceding table, 5AH = 90
■
❍
<Example 2> What is the decimal expression of the
value 12 34H given as hexadecimal for each 7 bits?
From the preceding table, since 12H = 18 and 34H = 52
18 x 128 + 52 = 2356
■
■ ■■
Examples of Actual MIDI Messages
■
❍
<Example 1> 92 3E 5F
9nH is the Note-on status, and n is the MIDI channel number. Since 2H = 2, 3EH =
62, and 5FH = 95, this is a Note-on message with MIDI CH = 3, note number 62 (note
name is D4), and velocity 95.
■
❍
<Example 2> C9 20
CnH is the Program Change status, and n is the MIDI channel number. Since 9H = 9
and 20H = 32, this is a Program Change message with MIDI CH = 10, program number
33.
■
❍
<Example 3> E1 00 28
EnH is the Pitch Bend Change status, and n is the MIDI channel number. The 2nd byte
(00H=0) is the LSB and the 3rd byte (28H=40) is the MSB, but Pitch Bend Value is a
signed number in which 40 00H ( = 64 x 128 + 0 = 8192) is 0, so this Pitch Bend Value is
28 00H - 40 00H = 40 x 128 + 0 - (64 x 128 + 0) = 5120 - 8192 = -3072
If the Pitch Bend Sensitivity is set to 2 semitones, -8192 (00 00H) will cause the pitch to
change -200 cents, so in this case -200 x (-3072) / (-8192) = -75 cents of Pitch Bend is
being applied to MIDI channel 2.
■
❍
<Example 4> B3 64 00 65 00 06 0C 26 00 64 7F 65 7F
BnH is the Control Change status, and n is the MIDI channel number. For Control
Changes, the 2nd byte is the control number, and the 3rd byte is the value. In a case
in which two or more messages consecutive messages have the same status, MIDI
has a provision called "running status" which allows the status byte of the second
and following messages to be omitted. Thus, the above messages have the following
meaning.
B3 64 00
MIDI ch.4, lower byte of RPN parameter number: 00H
(B3) 65 00
(MIDI ch.4) upper byte of RPN parameter number: 00H
(B3) 06 0C
(MIDI ch.4) upper byte of parameter value: 0CH
(B3) 26 00
(MIDI ch.4) lower byte of parameter value: 00H
(B3) 64 7F
(MIDI ch.4) lower byte of RPN parameter number: 7FH
(B3) 65 7F
(MIDI ch.4) upper byte of RPN parameter number: 7FH
In other words, the above messages specify a value of 0C 00H for RPN parameter
number 00 00H on MIDI channel 4, and then set the RPN parameter number to 7F 7FH.
RPN parameter number 00 00H is Pitch Bend Sensitivity, and the MSB of the value
indicates semitone units, so a value of 0CH = 12 sets the maximum pitch bend
range to ± 12 semitones (1 octave). (On this device, the LSB of Pitch Bend Sensitivity
is ignored, but the LSB should be transmitted anyway (with a value of 0) so that
operation will be correct on any device.)
Once the parameter number has been specified for RPN, all Data Entry messages
transmitted on that same channel will be valid, so after the desired value has been
transmitted, it is a good idea to set the parameter number to 7F 7FH to prevent
accidents. This is the reason for the (B3) 64 7F (B3) 65 7F at the end.
It is not desirable for performance data (such as Standard MIDI File data) to contain
many events with running status as given in. This is because if playback is halted
during the song and then rewound or fast-forwarded, the sequencer may not be able
to transmit the correct status, and the sound generator will then misinterpret the data.
Take care to give each event its own status.
