*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. What is the decimal expression of 5AH ? From the preceding table, 5AH = 90 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 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 with MIDI CH = 3, note number 62 (note name is D4), and velocity 95. CE 08 CnH is the Program Change status, and n is the MIDI channel number. Since EH = 14 and 08H = 08, this is a Program Change message with MIDI CH = 15, program number 08 (Strings in F-50). B3 64 00 65 01 06 40 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 01 (MIDI ch.4) upper byte of RPN parameter number: 01H (B3) 06 40 (MIDI ch.4) upper byte of parameter value: 40H (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 40 00H for RPN parameter number 00 01H (Master Fine Tuning) on MIDI channel 4, and then set the RPN parameter number to 7F 7FH (RPN null). 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. . Example of an Exclusive message and calculating a Checksum Roland Exclusive messages (DT1) are transmitted with a checksum at the end (before F7) to make sure that the message was correctly received. The value of the checksum is determined by the address and data of the transmitted exclusive message. . How to calculate the checksum (hexadecimal numbers are indicated by ‘H’) The checksum is a value derived by adding the address, size and checksum itself and inverting the lower 7 bits. Here’s an example of how the checksum is calculated. We will assume that in the exclusive message we are transmitting, the address is aa bb and the data or size is ccH. aa + bb + cc = sum sum . 128 = quotient ... remainder 128 - remainder = checksum Set “Reverb Type” to “Type 4” According to the Parameter Address Map, the Address of Reverb Type is 01 03H, and the Value corresponding to Type 4 is 30H. So, the message should be : F0 41 00 1A 12 01 03 30 ?? F7 ---------------- - -- (1) (2) (3) (4) (5) address data checksum (6) (1) Exclusive Status (2) ID (Roland) (3) Device ID (UNIT#-1) (4) Model ID (F-50) (5) Command ID (DT1) (6) End of Exclusive * UNIT NUMBER is always the same as the current MIDI Tx/Rx channel. In this example, the MIDI Tx/Rx channel is 1. Next we calculate the checksum. 01H + 03H + 30H = 1 + 3 + 48 = 52 (sum) 52 (sum) . 128 = 0 (quotient) ... 52 (remainder) checksum = 128 - 52 (remainder) = 76 = 4CH Therefore, the message to send is : F0 41 00 1A 12 01 03 30 4C F7 . About tuning F-50 is tuned by sending RPN #1 (Master Fine Tuning) to the appropriate MIDI Rx channel. RPN #1 allows tuning to be specified in steps of approximately 0.012 cents (to be precise, 100/8192 cent). One cent is 1/100th of a semi-tone. Frequently used tuning values are given in the following table for your reference. Values are in hexadecimal (decimal in parentheses). +————————+————————+——————————————+ |Hz at A4| cent | RPN #1 | +————————+————————+——————————————+ | 445.0 | +19.56 | 4C 43 (+1603)| | 444.0 | +15.67 | 4A 03 (+1283)| | 443.0 | +11.76 | 47 44 (+ 964)| | 442.0 | + 7.85 | 45 03 (+ 643)| | 441.0 | + 3.93 | 42 42 (+ 322)| | 440.0 | 0 | 40 00 ( 0)| | 439.0 | — 3.94 | 3D 3D (— 323)| | 438.0 | — 7.89 | 3A 7A (— 646)| +————————+————————+——————————————+ Set the tuning of F-50 to A4 = 442.0 Hz Send RPN#1 to the MIDI Tx/Rx channel. From the above table, the value is 45 03H. If the MIDI Tx/Rx channel is set to ch.1, below is the message we transmit. B0 64 00 MIDI ch.1, lower byte of RPN parameter number: 00H (B0) 65 01 (MIDI ch.1) upper byte of RPN parameter number: 01H (B0) 06 45 (MIDI ch.1) upper byte of parameter value: 45H (B0) 26 03 (MIDI ch.1) lower byte of parameter value: 03H (B0) 6...
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