One criticism I got could need further technical advice: the quality of the vocals. I just used my smartphone to record my voice, and I guess, I had trouble to get the voice to the volume, I wanted, so there are often two tracks with the vocal samples. Do you have same tipps for me?
While smartphones are pretty amazing all-round devices these days, I wouldn't rely on them for recording. Their microphones are typically not designed for the best possible quality but for small size, and you never know what kind of post-processing is applied on the software side. A good field recorder / dictation device or desktop microphone would probably sound better and isn't all that expensive. Generally there are many techniques to add volume and power to samples, including effects such as compressors / limiters, reverb and equalizers. This is a broad topic that cannot be summarized in a single forum post, but there are many tutorials explaining that kind of stuff. It requires effort but so do all self-recorded samples if you want them to sound good.
Double-tracking (recording the same vocals twice, as you did) is also a common technique in music production to add volume, but to be honest you didn't seem to spend any effort on it: The two samples playing at once e.g. in "Theorie" have completely different timing, so syllables from the same word appear at slightly different times, and more importantly, with completely different intonation, which sounds pretty bad to my ears. If you want good results, you cannot just recording the same vocal lines twice - you have to do it again and again until you have two samples that fit together, with timing and intonation as closely together as possible. Everything else will just be perceived as poor quality.
