Cello Practice and Recording Room

Your recordings sound great! Bravo! Usually a recording sounds boxy or canny in a small room but yours sound bigger with smoother reverb and a a bit of decay as if you used a fine digital reverb (easy to come by these days). Close micing helps poor acoustics. Your room looks to be untreated so for recording and practicing, eliminating flutter echoes and reflections from walls will help if your listening/playing position sounds like it needs help but your recordings sound good to me.

The ambience of a small bedroom will never sound as good as a larger concert hall, or even a medium size school band room. So the best you can aim for is a neutral sound with minimal reflections and comb filtering. You can also minimize "room sound" by putting the microphone close to the instrument, though that can have other problems. I agree with Rock that your recording sounds good, but I still hear a hint of room sound. The standard treatment for a bedroom size space is to cover about 30 percent of the wall surface with absorbers in a stripes or checkerboard pattern. A cello can play down to 65 Hz, though there isn't much energy that low. But still, a cello is a "bass" instrument, so the absorption should be at least two inches thick if not three inches. When recorded the sound will be clean, but dry. So then you can add reverb with software later. Even a free reverb plug-in will sound better than the natural ambience of a small room.