Export to iTunes in Acc file format creates distortion in the track
When I export/share an acoustic guitar recording (single track) created in GarageBand to ITunes in ACC file format, The sound quality is diminished significantly. It creates crackling and fuzziness on the notes I hit a little harder, as though I set the recording level too high. But in fact I deliberately set the recording level very low (even big notes stay in the green) to avoid this happening. And as I said, the recording sounds tolerable (not exceptional sound quality, but passable) during playback in GarageBand, before sharing to iTunes.
I didn't experience this problem with the original version of GarageBand that came with the computer (version 6?) - the one export I did with this earlier version, that is. But settings were a little different there, and maybe I just lucked out the first time. I updated to version 10.2.0, and it appears that is when I began having problems.
I'm using a Rode NT-USB microphone and listening to playback through a set of Audio Technica earphones with a plug-in jack (not Bluetooth).
I have an early 2015 MacBook Pro. The version of iTunes I have on the machine is 12.7.3.46. I never used GarageBand until a month or so ago, so I'm still on the learning curve. Still, should it be this difficult to get a good sounding export from GarageBand?
My sincere thanks for any input/recommendations.
MacBook Pro with Retina display, macOS High Sierra (10.13.2), recorded with a RODE NT-USB mic