It seems that processing note off with this plugin is weird... Once it processes note off, then it will not anymore, keeping note on state forever.

When I use this plugin on a host, whenever it gets activated, other audio apps start sounding like having noise filters.

If I apply EQ to cut low band width like this sshot (DISTRHO 3 Band EQ), it goes away, which likely means ayumi outputs some glitchy unheard "noisy" wave output. I cannot hear such noise as the plugin by itself, so it is likely result of additive audio outputs.

The final sample output is calculated like this:

  ay->left = decimate(fir_left);
  ay->right = decimate(fir_right);

Maybe they need some filtering after call to decimate(). I have no right idea what it would be like though.

noise needs 5 bits, and mixer needs 3 bits. It is fine on PC registers, but not as a MIDI message (should be 7 bits).

There is some rough and inaccurate assumption when note_on is transformed into call to ayumi_set_tone(). There seems some conversion formula to map to the actual address values (e.g. on ym2149-test).