> If I open gb, where I can see, are the software instruments in mono or in stereo? There's no visual indicator, an Instrument track is what it is, stereo or mono. What are you trying to do that requires you to change Tracks or Projects from mono or stereo..? I don't understand what you're going for here.. > the song will be in stereo, not mono anymore... I don't understand what menu options you're referring to there.. Exported songs [Projects] are always in stereo. If you wanted to export [Share] a Project as a mono bounce instead of stereo, you could insert a Direction Mixer in the Master Track and set Spread to 0.00. That'll squeeze all the tracks into the center of the mix, but the bounced file will still be stereo [2-channel], even thought the audio will be mono. Again, what exactly are you trying to do..?

Why I'd want to adjust a width of an instrument track? What it gives to me? Does the quality of song is the same, with adjusted width and before it?

Experienced mixers position [pan] the various tracks at different locations between the speakers in the stereo soundfield to optimize clarity and to create a pleasing soundstage. If you go through the MPV course library and check out some of the courses that touch on mixing, you might get some ideas about how to utilize panning and the stereo soundstage.

So adjusting a width of an instrument track is a panning, in other words an automation? If I don't use it, is the quality of song still good.. ? Do the all music styles like adjusting the width of an instrument track?

No, panning is positioning the apparent location of the track/instrument between the left & right speakers. Panning different tracks to different positions can enhance the clarity of the mix. Panning is *not* Automation -- usually the pan potion would be fixed for the length of the song (though you could optionally automate the pan position if you wanted it to change during the song). With different styles of music, there are conventions when it comes to panning -- for example, in pop music it's pretty standard to pan the kick, snare, bass, and lead vocal in the center, with other instruments/voices panned around them, to the left and right of center. But ultimately it's up to the mixer.. In most DAWs you can pan the left & right sides of a stereo track partially left & right to adjust the width of the stereo image, but the Pan knobs in GarageBand don't seem to offer this. However, the width of a stereo track can be adjusted with the Direction Mixer plug-in -- I explained that earlier in this thread.