Hi Nonchai,

It's important to remember that Band-in-a-Box isn't a DAW, so if you expect it to behave like one, you're going to be disappointed.

The only track that can be played with your keyboard is the Thru track. If you put a plugin on your Melody track, you will not hear that plugin when you play on the keyboard. You can use the keyboard to record notes onto the Melody track, and you'll hear the plugin on playback, but what you hear during recording is what's on the Thru track.

Have you tried assigning Synthmaster to the Thru track? That's the only way to do what you've described.

Thanks
Kent
PG Music