I get asked this often. It really depends on what you mean by ‘quality’. If you’re talking about the sound quality output, it has some limitations. I love GarageBand for students stepping into learning to write music and record because it’s creative user friendly and it also has limited options so it’s not overwhelming. ‘Logic’ is the pro version of GarageBand. If I were a beginner, I would start working and learning in GarageBand and then when I start growing into it, upgrade to Logic. The great thing is that you won’t loose any files. They can all be opened up and converted to Logic files. The sound limitations I was talking about are related to the sampling rate. It’s kind of like pixels for images. The higher sampling rate the better detail and quality sound you’ll get. You may not even hear the difference in the beginning especially just with instruments.
The area you probably will hear a difference is in the vocals. One of the most important things you need for good vocals is a decent tube mic. Do not use your computer’s mic. The sound quality will be poor with a lot of fuzzy white noise added in. Also, don’t use dynamic mics as they are meant for live sound (mostly) and won’t usually have a hot enough gain to get a good clean vocal. All of that being said, GarageBand just doesn’t really have the tools (great compressors, etc.) to really get great vocals. If you going to dive into vocals, you’ll probably need to upgrade to Logic to get a good sound. You could always record and learn with the thought of replacing your vocals down the road once you upgrade.
Now, to the other part of the question which involves ‘limited musical training’. It really depends. Some creative people that write have a lot of natural intuition about what works. That was certainly the case for me. I wrote a lot of music before I really understood what I was doing. Dive in and do it if you have ideas. I can also tell you that my writing got better when I was able to use an understanding of how music works (theory) alongside my natural inspiration and ideas. Especially when you get ‘stuck’. When I get to those points where the idea doesn’t just flow out of me, I can logic my way through the problem area. For instance, I might know what melody note I wanted but can’t find a chord that has the feeling I want to evoke. I can start thinking about what kinds of emotion or feel certain chord qualities have and start to narrow it down from there. Or I can just start trying every chord that has that melody note in it. That’s just one example. I might also get stuck because an idea is too repetitious and I need to create some contrast. I know lots of ways to create contrast, so I can try out different ways to get the effect I need.
My advice is to dive in and start working with GarageBand and to also start trying to improve musical skills and knowledge. It’s only going to help to bring your ideas into the real world. You certainly don’t have to be an amazing player in order to write music as long as you learn how to edit properly. Good playing skills certainly make things faster and easier but it shouldn’t stop you from creating. Another great way to learn is to cowrite. You can learn a lot and also probably write music that is different than you would create all on your own.