Photosounder is described as 'is the first audio editor/synthesizer to transform any sound as an image and to create any possible sound from an image. It have an entirely image-based approach to sound creation and editing' and is an app in the Audio & Music category. There are three alternatives to Photosounder for a variety of platforms, including Android, iPad, iPhone, Linux and Windows. The best alternative is spectrogram, which is both free and Open Source. Other great apps like Photosounder are PhonoPaper (Free) and Virtual ANS (Free).
PhonoPaper is a camera app for playing pictures with encoded sound (PhonoPaper-codes). With this app, you can also create your own codes: 10 seconds of sound can be recorded from a microphone and converted into an image.
Virtual ANS is a software simulator of the unique Russian synthesizer ANS - photoelectronic musical instrument created by Evgeny Murzin from 1938 to 1958. The ANS made it possible to draw music in the form of a spectrogram (sonogram).