This App seems to be no more developed, but is still available in the App Store.
2 minor updates after that I made this review.
Published on 1 Oct 2013
FourierSynth Fourier Synthesiser allows students, engineers and musicians to study quantitatively the Fourier components of periodic waveforms. Real-time superposition of harmonically related sinusoids upto 15th harmonic can be viewed with the built in Time Domain display or alternatively viewed on an Oscilloscope connected to the audio stereo output. Those musically inclined can choose to listen to any two sinusoids or the sum of all selected sinusoids. Features: Select Sine and Cosine from fundamental to the 15th harmonic. See how convergence to the ideal improves with more components Fundamental frequency adjustable from 50Hz to 1kHz Individually control amplitude and On/Off state of each harmonic DC term available on iPad display Select from a range of 10 preset waveforms Square, Triangle, Sawtooth, Amplitude Modulation, Impulse, Half and Full Wave Rectification Monitor waveforms externally on an Oscilloscope or Listen to audio output Choose which sinusoid or 'sum' appear on display or audio output Listen to musical chords and hear the effects of phase change on their sound Use the full range of Swipe, Tap, Pinch, Tap&Hold Gestures tap harmonic component to toggle On or Off swipe up or down to set amplitude of each harmonic component, swipe faster for rapid adjustment, swipe slower for fine settting press & hold harmonic component to reset to previous amplitude change fundamental frequency with pinch in or out tap Time Domain display to toggle channel 1 On or Off pinch Time Domain display to change oscilloscope timebase swipe left/right to set horizontal position of oscilloscope display This is the App Store description. What can I add? Nothing... A little bit strict looking, but it is for students, so I suppose that's normal... :-).
Review by Ed
What's new In:
10 Oct 2014
Optimised for iOS 8
9 Oct 2013
Redesigned for iOS 7, aiso compatible with iOS 6