Roland Midi Implimentation GW-8 - Manual (Page 10)

10
MIDI Implementation
■ Example of an Exclusive Message and
Calculating a Checksum
Roland Exclusive messages 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 (or size) 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 cc ddH and the data or size is ee ffH.
aa + bb + cc + dd + ee + ff = sum
sum ÷ 128 = quotient ... remainder
128 - remainder = checksum
■ The Scale Tune Feature (address: 40 1x 40)
The scale Tune feature allows you to finely adjust the individual pitch of the notes from C
through B. Though the settings are made while working with one octave, the fine
adjustments will affect all octaves. By making the appropriate Scale Tune settings, you can
obtain a complete variety of tuning methods other than equal temperament. As examples,
three possible types of scale setting are explained below.
❍ Equal Temperament
This method of tuning divides the octave into 12 equal parts. It is currently the most widely
used form of tuning, especially in occidental music. On the GW-8, the default settings for
the Scale Tune feature produce equal temperament.
❍ Just Temperament (Tonic of C)
The principal triads resound much more beautifully than with equal temperament, but this
benefit can only be obtained in one key. If transposed, the chords tend to become
ambiguous. The example given involves settings for a key in which C is the keynote.
❍ Arabian Scale
By altering the setting for Scale Tune, you can obtain a variety of other tunings suited for
ethnic music. For example, the settings introduced below will set the unit to use the Arabian
Scale.
Example Settings
Note name Equal Just Temperament Arabian Scale
Temperament(Key-tone C)
C 0 0 -6
C# 0 -8 +45
D 0 +4 -2
Eb 0 +16 -12
E 0 -14 -51
F 0 -2 -8
F# 0 -10 +43
G 0 +2 -4
G# 0 +14 +47
A 0 -16 0
Bb 0 +14 -10
B 0 -12 -49
The values in the table are given in cents. Convert these values to hexadecimal, and transmit
them as Exclusive data.
For example, to set the tune (C-B) of the Part 1 Arabian Scale, send the following data:
F0 41 10 42 12 40 11 40 3A 6D 3E 34 0D 38 6B 3C 6F 40 36 0F 76 F7
GW-8_MIDIImple_e.fm 10 ページ ２００８年７月１８日 金曜日 午前９時２分