MIDI Implementation
■Examples of Actual MIDI Messages
<Example 1> 92 3E 5F
9n 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 of MIDI CH = 3, note number 62 (note name D4) and velocity 95.
<Example 2> CE 49
CnH is the Program Change status and `n' is the MIDI channel number. Since EH = 14, and 49H = 73, this is a Program Change message of MIDI CH = 15, Program number 74 (in the GS sound map, Flute).
<Example 3> EA 00 28
EnH is the Pitch Bend Change status and `n' is the MIDI channel number. The 2nd byte (00H=0) is the LSB of the Pitch Bend value, and the 3rd byte (28H=40) is the MSB. However since the Pitch Bend is a signed number with 0 at 40 00H (= 64 x 128 + 0 = 8192), the Pitch Bend value in this case is 28 00H - 40 00H = 40 x 128 + 0 - (64 x 128 + 0) = 5120 - 8192 = -3072
If we assume that the Pitch Bend Sensitivity is set to two semitones, the pitch will change only -200 cents for a Pitch Bend value of -8192 (00 00H). Thus, this message is specifying a Pitch Bend of -200 x (-3072) / (-8192) = -75 cents on MIDI CH = 11.
<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. In Control Change messages, the 2nd byte is the controller number, and the 3rd byte is the parameter value. MIDI allows what is known as “running status,” when if messages of the same status follow each other, it is permitted to omit the second and following status bytes. In the message above, running status is being used, meaning that the message has the following content.
B3 64 00 | MIDI CH = 4, RPN parameter number LSB: 00H |
(B3) | 65 | 00 | MIDI CH = 4, RPN parameter number MSB: 00H |
(B3) | 06 | 0C | MIDI CH = 4, parameter value MSB: 0CH |
(B3) | 26 | 00 | MIDI CH = 4, parameter value LSB: 00H |
(B3) | 64 | 7F | MIDI CH = 4, RPN parameter number LSB: 7FH |
(B3) | 65 | 7F | MIDI CH = 4, RPN parameter number MSB: 7FH |
Thus, this message transmits a parameter value of 0C 00H to RPN parameter number 00 00H on MIDI CH = 4, and then sets the RPN parameter number to 7F 7FH.
The function assigned to RPN parameter number 00 00H is Pitch Bend Sensitivity, and the MSB of the parameter value indicates semitone steps. Since the MSB of this parameter value is 0CH = 12, the maximum width of pitch bend is being set to [+/-] 12 semitones (1 octave) (GS sound sources ignore the LSB of Pitch Bend Sensitivity, but it is best to transmit the LSB (parameter value 0) as well, so that the message can be correctly received by any device.
Once the parameter number has been set for RPN or NRPN, all subsequent Data Entry messages on that channel will be effective. Thus, it is recommended that after you have made the change you want, you set the parameter number to 7F 7FH (an “unset” or “null” setting). The final (B3) 64 7F (B3) 65 7F is for this purpose.
It is not a good idea to store many events within the data of a song (e.g., a Standard MIDI File song) using running status as shown in <Example 4>. When the song is paused, fast- forwarded or rewound, the sequencer may not be able to transmit the proper status, causing the sound source to misinterpret the data. It is best to attach the proper status byte to all events.
It is also important to transmit RPN or NRPN parameter number settings and parameter values in the correct order. In some sequencers, data events recorded in the same clock (or a nearby clock) can sometimes be transmitted in an order other than the order in which they were recorded. It is best to record such events at an appropriate interval (1 tick at TPQN=96, or 5 ticks at TPQN=480).
*TPQN: Ticks Per Quarter Note (i.e., the time resolution of the sequencer)
■Examples of Exclusive Messages and
Calculating the Checksum
Roland exclusive messages (RQ1, DT1) are transmitted with a checksum at the end of the data (before F7) to check that the data was received correctly. The value of the checksum is determined by the address and data (or size) of the exclusive message.
❍How to Calculate the Checksum
(hexadecimal values are indicated by a “H”)
The checksum consists of a value whose lower 7 bits are 0 when the address, size and checksum itself are added.
The following formula shows how to calculate the checksum when the exclusive message to be transmitted has an address of aa bb cc ddH, and data or size of ee ffH.
aa+ bb + cc + dd + ee + ff = total total / 128 = quotient ... remainder 128 - remainder = checksum
<Example 1> Setting the Performance Common REVERB TYPE to DELAY (DT1)
The “Parameter Address Map” indicates that the starting address of the Temporary Performance is 01 00 00 00H, that the Performance Common offset address is 00 00H, and that the REVERB TYPE address is 00 28H. Thus, the address is:
01 00 00 00H
00 00H
+) 00 28H 01 00 00 28H
Since DELAY is parameter value 06H,
F0 | 41 | 10 | 6A | 12 | 01 00 00 28 | 06 | ?? | F7 |
(1) | (2) | (3) | (4) | (5) | address | data | checksum | (6) |
(1) Exclusive status | (2) ID number (Roland) | (3) Device ID (17) | |
(4) Model ID (JV-1010) | (5) Command ID (DT1) | (6) EOX | | |
Next we calculate the checksum.
01H + 00H + 00H + 28H + 06H = 1 + 0 + 0 + 40 + 6 = 47 (sum) 47 (total) / 128 = 0 (quotient) ... 47 (remainder)
checksum = 128 - 47 (quotient) = 81 = 51H
This means that the message transmitted will be F0 41 10 6A 12 01 00 00 28 06 51 F7.
<Example 2> Retrieving data for USER:03 Performance Part 3 (RQ1)
The “Parameter Address Map” indicates that the starting address of USER:03 is 10 02 00 00H, and that the offset address of Performance Part 3 is 12 00H. Thus, the address is:
10 02 00 00H
+) 12 00H 10 02 12 00H
Since the size of the Performance Part is 00 00 00 19H,
F0 | 41 | 10 | 6A | 11 | 10 02 12 00 | 00 00 00 19 | ?? | F7 |
(1) | (2) | (3) | (4) | (5) | address | size | checksum | (6) |
(1) Exclusive status | (2) ID number (Roland) | (3) Device ID (17) | |
(4) Model ID (JV-1010) | (5) Command ID (RQ1) | (6) EOX | | |
Next we calculate the checksum.
10H + 02H + 12H + 00H + 00H + 00H + 00H + 19H = 16 + 2 + 18 + 0 + 0 + 0 + 0 + 25 = 61 (sum)
61 (total) / 128 = 0 (product) ... 61 (remainder) checksum = 128 - 61 (remainder) = 67 = 43H
Thus, a message of F0 41 10 6A 11 10 02 12 00 00 00 00 19 43 F7 would be transmitted.
