Another iOS instrument, but this one is a breath of fresh air in an App Store overstocked with virtual analogue synths and sampled drums.
SynthTronica brings the rather scientific sounding formant distortion synthesis to the iPad. This uses Fourier analysis of samples to come up with a spectral filter that varies over time (a 'formant' in SynthTronica-speak), and superimposes this on a pair of pulse waves. It's a bit like a vocoder, and thankfully, you don't need a PhD in Synthology to use the app.
Source samples (for the formants) can be imported, recorded with the iPad's mic or resampled from within the app itself. The recorded bits can be edited; you can change the start and end points of the loops and truncate the excess. The instrument's Synth View consists of pulse width adjustment, oscillator mix and sync, and an LFO (here called LFM).
The filter section has its own page and a multitouch panel for manipulating it - swoosh your fingers around and a resonant node is created for each one. More typical is the ADSR envelope for the amplitude.
Like most synth apps, there's a built-in keyboard with which you can play your sounds. You can choose from three layouts and various scales and tunings. One cool iPad-friendly feature is a 'hold' button that sustains the sound indefinitely while you tweak settings (eg, the filter). You can record your performances and export them as 16- or 24-bit WAV/AIFF (import and export is handled via iTunes), or save them as new formants.
Spectral choirs, cosmic tinklings and pulsating pads are easy to come by using SynthTronica. Vocoding is a snap with this thing. Ambient and New Age musicians are going to eat it up, but it could easily fit into any electronic style. It's not without flaws: many of the presets sound too similar, and we experienced occasional instability when editing and saving our own formants. Still, it's a good buy, although we understand that the current price is an introductory one - act fast and you might be able to grab it before the increase.