A couple of months ago, I was given the opportunity to review a number of synth apps for the iPhone. In that round-up, I took a look at noise.io pro, one of the deepest and richest apps I've come across.
iPhone and iPad apps tagged "music synthesizer."
Synth Round-Up: Synthesizers Break Free from the Studio on the iPhone
Musicians of all calibres, from mom's basement amateurs to true prodigies, can now find the software they need to make music on the go on their iPhones, whenever and wherever they want. But with so many options, it's often hard for people to figure out which app suits them best.