This app can be used to generate different tones by defining the wave form the frequency and the amplitude. The resulting sound wave is visualized as a graph. By now the following wave forms are supported: Sine Square Triangle and Sawtooth.

Additionally this app supports ring and amplitude modulation. Modulation means that the amplitude of carrier wave is changed dynamically by a modulator wave. Basically the two waves are multiplied. For low modulation frequencies this creates a tremolo effect. For higher frequencies from about 20hz the individual vibrations are no longer recognized which causes the creation of frequency side bands. This can create some very interesting sound effects. For further information about how modulation works I recommend reading the following article: https://en.wikibooks.org/wiki/Sound_Synthesis_Theory/Modulation_Synthesis

For the graph visualization the open-source library MPAndroidChart is used which was created by PhilJay and is licensed under the Apache 2.0 license. The github repository to this library can be found under: https://github.com/PhilJay/MPAndroidChart