The idea behind Song Studio HD is very good. It comes with nine beats installed and you can record yourself singing, beat boxing or rapping over those beats. When you start the app, press the "setup" button and then choose which beat to use. The app will then play the beat and you can record your voice. Once done, all completed songs are saved to the "My Songs" menu, though there is no way to change the names of these songs, so if you use the app extensively, it will get confusing as to which songs are which.
The recording works well, the beats are sufficient for making some basic, fun songs and the interface is adequate, despite the relatively intrusive ads. Some features, such as the "Drums" don't appear to have any purpose in the app. You can press the drums and they make sounds, but they don't record properly and there is no separate record button within the drums menu. The paid version will remove the ads, which may be worthwhile if you use the app a lot, but with only nine songs and limited saving and customization options, it is unlikely you will use this app for much longer than the initial recordings.
Song Studio HD is a fun app that offers a nice diversion and an intuitive interface. It would provide a good laugh for a night at home with friends and children could easily spend hours recording, tweaking and rerecording their very own songs. As a free app, it offers plenty to enjoy, but it doesn't quite warrant an upgrade to the paid version. With some odd design choices and missing options, there is much room for improvement.