And one question more:

What does 'sum' mean in the specification below:

SYSEX GS USE FOR RHYTHM PART

        [ F0 41 10 42 12 40 1x 15 mm sum F7 ]

        x : 1 - 9 => 0 - 8 channel / 0 => 9 channel / A - F => 11 - 16 channel

        mm : 0 => normal part / 1,2 => set to drum track

With SysEX mesages for GS devices the penultimate byte is a checksum as detailed in several of the GS device specifications.
(See the manual for the SC-8850, where I found it in the past.)

JohnG.

The GS file called test-sysex-gs-40-1x-15-drum-part-change.mid is available at https://github.com/jazz-soft/test-midi-files
An XG example at http://midkar.com/MidiStudio/ERock/Spice_Girls_Wannabe_XG.mid uses drums on channels 9, 10, 11 via "Bank select" and "Program Change" messages.

Quoted from Nikolai on Friday, 05 November 2021

What does 'sum' mean in the specification below:

You can have a look at my tutorial to understand how the checksum works.

Thank you for all the answers and the samples.

One more thing I am confused about is if GS can convert a channel to drums in the middle of the song? or if it always applies to whole song. The message was called non-realtime in the spec, which leads me to believe its only for whole song, but I don't know..

Quoted from Sema on Friday, 05 November 2021

The GS file called test-sysex-gs-40-1x-15-drum-part-change.mid

Am I reading it wrong or is this a GM file? I didn't find the F0 41 10 42 12 40 00 7F 00 41 F7 in it..
So it should not be legal for it to change drum parts, right?

Quoted from Nikolai on Friday, 05 November 2021

Am I reading it wrong or is this a GM file? I didn't find the F0 41 10 42 12 40 00 7F 00 41 F7 in it..
So it should not be legal for it to change drum parts, right?

Changing drum parts is legal, but that makes the MIDI file incompatible with non-GS synths.

SMF:

  type: 0

  ppqn: 96

  tracks: 1

MTrk:

  0: ff03 -- Sequence Name: GS Drum Part Change Test

  0: ff02 -- Copyright: https://jazz-soft.net

  0: ff01 -- Text: Changing the drum channel on GS-compatible synths.\n

  0: f0 41 7f 42 12 40 00 7f 00 41 f7 (GS Reset)

  0: f0 41 7f 42 12 40 11 15 02 18 f7 (GS Drum Part Change)

  0: ff01 -- Text: If your synth supports GS you must hear drum playing on channel 0

  0: 90 30 7f -- Note On

  96: 80 30 40 -- Note Off

  96: 90 34 7f -- Note On

  192: 80 34 40 -- Note Off

  192: 90 37 7f -- Note On

  288: 80 37 40 -- Note Off

  288: 90 3c 7f -- Note On

  384: 80 3c 40 -- Note Off

  576: f0 41 7f 42 12 40 10 15 00 1b f7 (GS Drum Part Change)

  576: ff01 -- Text: If your synth supports GS you must hear piano playing on channel 9

  576: 99 30 7f -- Note On

  672: 89 30 40 -- Note Off

  672: 99 34 7f -- Note On

  768: 89 34 40 -- Note Off

  768: 99 37 7f -- Note On

  864: 89 37 40 -- Note Off

  864: 99 3c 7f -- Note On

  960: 89 3c 40 -- Note Off

  1152: ff01 -- Text: Thank you!

  1152: ff2f -- End of Track

Quoted from Sema on Friday, 05 November 2021

[code] 0: f0 41 7f 42 12 40 00 7f 00 41 f7 (GS Reset)

But why 7F instead of 10? All the specs I looked at showed 41 10 42 ...etc

Third byte is the device ID. 10 means for the device 10, 7f means for all devices.
Check the specs

Ah, cool. Didn't know that, thanks.

Here's a GS file with drums on 10 and 11, type 0.

Another GS, drums on 10 and 11, type 1.

FYI, here is my code from my instrument changer to check for GS percussion assignment on a non-standard channel:

							// GS Custom Percussion Assignment

							// F0 0A 41 (10) 42 12 [40 1A 15] [02] 0F F7 

							// [.. 1x ..] x = part# / (probably) ch# 1-9, 0, A-F

							// [0y] y = type: 0 = standard, 1 = drum map 1, 2 = drum map 2

							else if ((buffer_peek(global.edit_buffer, cur_pos, buffer_u8) == 0x41) &&

								/*(buffer_peek(global.edit_buffer, cur_pos + 1, buffer_u8) == 0x10) &&*/

								(buffer_peek(global.edit_buffer, cur_pos + 2, buffer_u8) == 0x42) &&

								(buffer_peek(global.edit_buffer, cur_pos + 3, buffer_u8) == 0x12) &&

								(buffer_peek(global.edit_buffer, cur_pos + 4, buffer_u8) == 0x40) &&

								/*(buffer_peek(global.edit_buffer, cur_pos + 5, buffer_u8) == 0x00) &&*/

								(buffer_peek(global.edit_buffer, cur_pos + 6, buffer_u8) == 0x15) &&

								/*(buffer_peek(global.edit_buffer, cur_pos + 7, buffer_u8) == 0x00) &&*/

								(buffer_peek(global.edit_buffer, cur_pos + 8, buffer_u8) == 0x0F) &&

								(buffer_peek(global.edit_buffer, cur_pos + 9, buffer_u8) == 0xF7))

								{

									part_num = buffer_peek(global.edit_buffer, cur_pos + 5, buffer_u8);

									part_num -= 0xF;

									part_type = buffer_peek(global.edit_buffer, cur_pos + 7, buffer_u8);

									global.custom_drums[part_num - 1] = part_type; 

								}

							buffer_seek(global.edit_buffer, buffer_seek_relative, v_length);

							break;

I read the F0 to trigger a SYSEX scan (all values in HEX). If the next byte is 0A then check for 41 (skip device ID) 42 12 40 (skip part number) 15 (skip type) 0F F7. If those all match, I then go back and read the part number and type.

XG is easier to determine percussion channels, as the MSB for a channel will either be set to 126 or 127.

GM can also have percussion set with MSB 120.

Quoted from Sema on Friday, 05 November 2021

f0 41 7f 42 12 40 00 7f 00 41 f7 (GS Reset)

Quoted from Nikolai on Friday, 05 November 2021

But why 7F instead of 10? All the specs I looked at showed 41 10 42 ...etc

Quoted from Sema on Friday, 05 November 2021

Third byte is the device ID. 10 means for the device 10, 7f means for all devices.
Check the specs

Only System Exclusive messages with Manufacturer IDs of 7E and 7F have their contents specified by the MIDI specs available on the midi.org website. In these messages, a Device ID of hex 7F represents "all devices".

System Exclusive messages with any other Manufacturer ID have their contents specified by the manufacturer that is assigned to that Manufacturer ID. My understanding is the Device ID in Roland System Exclusive messages is a value from hex 00 to hex 1F, and Roland products typically have a default device ID of hex 10. You can see information about the GS Reset message in manuals for Roland products that use GS, such as the Roland SC-8850 manual, which describes the GS Reset message on the bottom of page 230.

Quoted from Sema on Friday, 05 November 2021

The GS file called test-sysex-gs-40-1x-15-drum-part-change.mid

Sorry to keep asking about this file, but I am unsure I interpreted it correct.
Is this correct: ?

Change the first track to drums.
Change the second track to grand piano even though its on 10th channel.

Yes, that is correct.

It is NOT a 'rule' that drums should be on Ch 10 (midi data 09), merely a convention. This .mid file will be demonstrating that drums could happily be on Ch 0, and piano on Ch 10.

Geoff