SpectrumGen is a spectral synthesizer with a simple and effective user interface. It is a bit like the PixelWave experimental synth, but now you can draw the spectrum of sound!
• multitouch arpeggiator;
• export to WAV (via iTunes File Sharing);
• copy to share with another iOS sound apps;
• eight predefined timbres;
• changeable number of octaves (from 2 to 8);
• it is possible to draw the spectrum and play it at the same time;
• MIDI IN support;
• Audiobus and IAA support.
Dark colors - low frequencies (bass). Bright colors - high frequencies.
Also if you want to draw a waveform directly, check my other app - PixelWave.