Interfacing to MIDI (sequencer) devices via ALSA on Linux

[Fred vS]

Hello Mark.

What do you think about working together with the same (virtual) keyboard?
It could be easier to share our result.

Do you have vmpk installed?

If you have a Debian distro, just do:

Code: Bash  [Select][+][-]

1. > sudo apt install vmpk

I use this soundfont:

Code: Bash  [Select][+][-]

1. > sudo apt install fluid-soundfont-gm fluid-soundfont-gs

To load/run it, just type vmpk.

And later, do test with a real keyboard.

[EDIT] In attachment my config of vmpk using ALSA.  It works using synthesizer qsynth with this command: qsynth -a alsa

[Jurassic Pork]

Hello Fred,
Strange, for VMPK you have no output with aconnect -l command. Under Ubuntu 20.04 , it seems ok for me :

ubuntu$aconnect -l
client 0: 'System' [type=noyau]
    0 'Timer           '
    1 'Announce        '
client 14: 'Midi Through' [type=noyau]
    0 'Midi Through Port-0'
client 128: 'FLUID Synth (8160)' [type=utilisateur,pid=8160]
    0 'Synth input port (8160:0)'
client 129: 'VMPK Input' [type=utilisateur,pid=4584]
    0 'in              '
client 130: 'VMPK Output' [type=utilisateur,pid=4584]
    0 'out             '
ubuntu$aconnect 130:0 128:0
ubuntu$aconnect -l
client 0: 'System' [type=noyau]
    0 'Timer           '
    1 'Announce        '
client 14: 'Midi Through' [type=noyau]
    0 'Midi Through Port-0'
client 128: 'FLUID Synth (8160)' [type=utilisateur,pid=8160]
    0 'Synth input port (8160:0)'
   Connecté Depuis: 130:0
client 129: 'VMPK Input' [type=utilisateur,pid=4584]
    0 'in              '
client 130: 'VMPK Output' [type=utilisateur,pid=4584]
    0 'out             '
   Connexion À: 128:0

i have installed VMPK with synaptic some other packages have been installed (qsynth, soundfont etc...)

Friendly, J.P

[MarkMLl]

Debian 12: I only have "In" on vmpk, and that appears to be the client ID (i.e. set by the program) rather than a list of properties.

What appears to be happening is that if a source or destination device explicitly sets up its own mappings it can't also be managed using a connect: I can duplicate the behaviour using BeepDemo (another of the examples). It might be connected with exclusive access... I'm not touching the filter program while somebody else is looking at it but I'll see if I can stop BeepDemo working like that to make it more useful as a test program.

Use vkeybd which appears to work and has few dependencies.

Slightly later: Another possibility is probably Rosegarden, although that's almost certainly overkill unless  one is already editing scores.

I'm still not certain what's causing this. As far as I can tell the code used in BeepDemo doesn't (at least explicitly) grab exclusive access, and adding extra options doesn't help. Neither does explicitly disconnecting the port after use. I think I need to take a bit of a look at vkeybd's sourcecode, but that isn't going to happen right now.

I notice that BeepDemo does use some of the dedicated malloc/free calls, although not necessarily the subscription one that's causing the problem.

MarkMLl

[Jurassic Pork]

hello,

Debian 12: I only have "In" on vmpk, and that appears to be the client ID (i.e. set by the program) rather than a list of properties.

using the last stable version of vmpk (0.8.8 ) under Ubuntu 20.04 i have this :

ubuntu$aconnect -l
client 0: 'System' [type=noyau]
    0 'Timer           '
    1 'Announce        '
client 14: 'Midi Through' [type=noyau]
    0 'Midi Through Port-0'
client 128: 'MIDI In' [type=utilisateur,pid=5413]
    0 'in              '
client 129: 'MIDI Out' [type=utilisateur,pid=5413]
    0 'out             '
ubuntu$

only vmpk launched.

Friendly, J.P

[MarkMLl]

vmpk /looks/ much the same on Debian, but it doesn't behave the same. There's obviously some sort of stylistic trap into which one can fall when writing that type of program, until I have time to look at the relevant sources I won't speculate as to whether it's Ubuntu or Debian that's changing the default behaviour, or if it's based on vmpk's upstream version.

I spent a distasteful few hours a couple of weeks ago trying to work out how to get a Debian package to build with non-default options. I got something working, but then made the mistake of asking on StackExchange if anybody knew the "correct" way of grafting in that sort of thing... only to be told that my question wasn't specific enough. Jeez...

MarkMLl

[Fred vS]

Use vkeybd which appears to work and has few dependencies.

Hello Mark.

Ok,  vkeybd installed and working. 
Let do test with it.

Fre;D

[Jurassic Pork]

Debian 12: I only have "In" on vmpk, and that appears to be the client ID (i.e. set by the program) rather than a list of properties.

Debian 12 isn't the stable version of debian:   Ubuntu 20.04 use Debian 11

[Fred vS]

Hello Mark.

With vkeybd loaded:

Code: Bash  [Select][+][-]

1. > aconnect -l
2. client 0: 'System' [type=kernel]
3.     0 'Timer           '
4.         Connecting To: 142:0
5.     1 'Announce        '
6.         Connecting To: 142:0
7. client 14: 'Midi Through' [type=kernel]
8.     0 'Midi Through Port-0'
9. client 128: 'FLUID Synth (1086)' [type=user,pid=1086]
10.     0 'Synth input port (1086:0)'
11. client 129: 'Client-129' [type=user,pid=13388]
12.     0 'Virtual RawMIDI '
13. client 130: 'Virtual Keyboard' [type=user,pid=13404]
14.     0 'Virtual Keyboard'
15. client 142: 'PipeWire-System' [type=user,pid=1087]
16.     0 'input           '
17.         Connected From: 0:1, 0:0
18. client 143: 'PipeWire-RT-Event' [type=user,pid=1087]
19.     0 'input           '

Connecting with aconnect (no error message):

Code: Bash  [Select][+][-]

1. > aconnect 130:0 129:0

Connecting with your MidiFilter ( It works,  ,  but I did not catch how to disconnect first)

Code: Bash  [Select][+][-]

1. ~>MidiFilter-x86_64-linux-gtk2 -d 130:0 129:0
2. Subscribing 1 sources, PID 13667
3. Invalid ALSA subscription for source 0 (130:0): Device or resource busy.
4. free(): invalid pointer
5. fish: Job 1, '/home/fred/Downloads/asound/tru…' terminated by signal SIGABRT (Abort)
6.  

OK, I am ready to go further.

Fre;D

[TRon]

Debian 12 isn't a stable version :   Ubuntu 20.04 use Debian 11

Just a small correction/addition: That remark would implicate that Debian 12 would be (designated) unstable, which isn't true either. It is in testing, and in state of hard freeze per mar 12th 2023.

[Jurassic Pork]

Debian 12 isn't a stable version :   Ubuntu 20.04 use Debian 11

Just a small correction/addition: That remark would implicate that Debian 12 would be (designated) unstable, which isn't true either. It is in testing, and in state of hard freeze per mar 12th 2023.

Exact : Debian 12 isn't unstable but in testing state. Debian 11 is the version in the stable state.

[MarkMLl]

Enough of the API works to make me think that I've not totally screwed up my pointer handling: if anything I'm tending to be rather "un-Pascal" in order to keep the API as similar to the C-based one as possible to make asking questions of the upstream maintainers a bit less fraught.

If the API interface in the .pas files needs to be changed, I'll post the program that generates them automatically from the .inc file.

MarkMLl

[Fred vS]

Hello Mark.

OK, I did the test with a fresh reboot.

1) In terminal, load amidi (OK, loaded):

Code: Bash  [Select][+][-]

1. > amidi -p virtual -d

2) In other terminal, load vkeybd (OK, loaded)

Code: Bash  [Select][+][-]

1.  > vkeybd

3) In other terminal, check devices with aconnect -l

Code: Bash  [Select][+][-]

1. ~> aconnect -l
2. client 0: 'System' [type=kernel]
3.     0 'Timer           '
4.         Connecting To: 142:0
5.     1 'Announce        '
6.         Connecting To: 142:0
7. client 14: 'Midi Through' [type=kernel]
8.     0 'Midi Through Port-0'
9. client 128: 'FLUID Synth (1086)' [type=user,pid=1086]
10.     0 'Synth input port (1086:0)'
11. client 129: 'Client-129' [type=user,pid=17057]
12.     0 'Virtual RawMIDI '
13. client 131: 'Virtual Keyboard' [type=user,pid=17076]
14.     0 'Virtual Keyboard'
15. client 142: 'PipeWire-System' [type=user,pid=1087]
16.     0 'input           '
17.         Connected From: 0:1, 0:0
18. client 143: 'PipeWire-RT-Event' [type=user,pid=1087]
19.     0 'input  

4) In previous terminal 3), connect the keyboard with your MidiFilter:

Code: Bash  [Select][+][-]

1. > MidiFilter-x86_64-linux-gtk2 -d 131:0 142:0
2. Subscribing 1 sources, PID 17120

5) Playing some notes on the vkeybd keyboard, here the result from the waiting amidi first terminal 1):

Code: Bash  [Select][+][-]

1. > amidi -p virtual -d
2. 90397F
3. 803900
4. 903C7F
5. 803C00
6. 903E7F
7. 803E00
8. 90407F
9. 804000
10. 90417F
11. 804100
12. 90437F
13. 804300
14. 90437F
15. 804300
16. 90457F

Conclusion: your code works, let go further...

Fre;D

[MarkMLl]

If you edit GetFilteredEvents() you can select event types which /should/ get filtered out: the fact that I've not worked out how to do that is one of the issues.

I'm watching, but if I go quiet for a day or so it's because some "legal crap" has arrived which has to be dealt with promptly.

MarkMLl

[Fred vS]

Re-hello Mark.

It works with vmpk too ! 

Doing the same as previous post but using vmpk instead of vkeybd:

1) In terminal, run:

Code: Bash  [Select][+][-]

1. > amidi -p virtual

2) In other terminal,  run:

Code: Bash  [Select][+][-]

1. > vmpk

3) In other terminal, check devices with aconnect -l:

Code: Bash  [Select][+][-]

1. > aconnect -l
2. client 0: 'System' [type=kernel]
3.     0 'Timer           '
4.         Connecting To: 142:0
5.     1 'Announce        '
6.         Connecting To: 142:0
7. client 14: 'Midi Through' [type=kernel]
8.     0 'Midi Through Port-0'
9.         Connected From: 134:0
10. client 128: 'FLUID Synth (1086)' [type=user,pid=1086]
11.     0 'Synth input port (1086:0)'
12. client 129: 'Client-129' [type=user,pid=17492]
13.     0 'Virtual RawMIDI '
14. client 131: 'VMPK Input' [type=user,pid=17511]
15.     0 'in              '
16. client 134: 'VMPK Output' [type=user,pid=17511]
17.     0 'out             '
18.         Connecting To: 14:0
19. client 142: 'PipeWire-System' [type=user,pid=1087]
20.     0 'input           '
21.         Connected From: 0:1, 0:0
22. client 143: 'PipeWire-RT-Event' [type=user,pid=1087]
23.     0 'input

          '

4) In previous terminal 3), connect the keyboard with your MidiFilter (strange but it works with VMPK Output):

Code: Bash  [Select][+][-]

1. > MidiFilter-x86_64-linux-gtk2 -d 134:0 129:0
2. Subscribing 1 sources, PID 17590

5) Playing some notes on the vmpk keyboard, here the result from the waiting amidi first terminal 1):

Code: Bash  [Select][+][-]

1. > amidi -p virtual -d
2.  
3. 922E64
4. 822E00
5. 922F64
6. 822F00
7. 923064
8. 823000
9. 923164
10. 823100
11. 923264
12. 823200
13. 923364
14. 823300
15. 923464
16. 823400

[MarkMLl]

It works with vmpk too ! 

That's odd... it depends on whether vmpk's showing only an "in" or both an "In" and an "Out"... JP's example and your working ones are the latter case. Most likely a bug in vmpk, which isn't encouraging.

MarkMLl