It's harder because the program is trying to read chords. With solo piano, there is often no root (on what I heard) and few chords sounding, so perhaps there isn't enough information.

I haven't used the ACW except during beta testing because people pay me to do transcriptions, so I'm certainly not an expert on its use. There are good posts here that give instruction including the importance of establishing exactly where the song starts and where each measure falls. When these are set correctly with F8, I noticed that accuracy improves.

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