Tonma (./1) :
As I understand, wav files (after conversion) can be placed in the m1 Rom for adpcm A and B. But we can not read music (at least in loop), it's only sound effects ..For music we must use the YM2610. In v1 rom.

The two seem backwards here; sounds (ADPCM-A, ADPCM-B) go in the .v* roms, YM2610 driver control/Z80 code in the .m1 rom.

Tonma (./1) :
I tried the démos by Freem, the sound going well but we can not play a looped melody. correct.

The YM2610 only has native loop support for ADPCM-B; any ADPCM-A looping has to be done in software/Z80 code. (This is typically achieved by having loop point data somewhere in the M1 file, then watching Status 1 (Port 06) for the relevant channel to end playback, and finally set the new playback/ending points from the loop data in ROM.)

Tonma (./1) :
I tried with mvstracker (music and sound effects) but I have problems. I use sound.h, music and effects are played, but some times I have to repeat the command to play music and effects become less strong or null.

MVSTracker's ADPCM-A conversion is known to be flawed, which might explain why the sounds act odd.
I'm not fully sure as to why the music wouldn't work, but the MVSTracker driver doesn't work properly on real hardware (it's missing the required waits between address and data writes).

Tonma (./1) :
Can I use mvstracker with Datlib/Neobitz? Can I use midi files to create music ?

I believe one of the versions of Frog Feast (don't recall if it was the cart or CD version) used the MVSTracker library with the NeoBitz kit.

For MIDI, you would have to use a module tracker that allows importing MIDI files (such as OpenMPT), then convert to MOD and import that MOD in MVSTracker. However, only the first four channels will be used, and you will have to re-assign instruments.

Music creation for the Neo-Geo is in a pretty sad state at the moment, as to take full advantage of the YM2610, a new sound driver and tracker (or converter) would have to be created. I did start work on a music driver, but it's nowhere near complete, and a lot of things are going over my head (in terms of understanding things).