Mostly I use TouchOSC on an ipod to control DAWs, software and hardware synthesizers. TouchOSC is available in the Apple app store for iphone/ipod and ipad. I use it in combination with the iConnect Midi interface which allows for the connection of a variety of controllers and synths. I think, TouchOSC is suitable in the case of mimic faders, switches and knobs but the haptics of a touchscreen has in general some limitations to use it as a drum pad or keyboard controller. However, I am really satisfied with the options. TouchOSC comes with a PC/Mac based editor and a small librarian, downloadable from the hexler.net website. The self-made controller scenes can be transfered to the ipod (iphone) via itunes or wlan and here are some of my settings which I have found to be useful in the most of my situations. If you like to get these scenes please contact me via soundcloud.
This is a simple 1 octave keyboard. Depending on the touch down location on a key an additional value of a MIDI controller is sent, which is similar to the Animoog app or the Endeavour Evo keyboard. Here is a link which describes the principle of such a sensor-key on the Evo. The green button in the left corner allows for MIDI-mapping of the “sensor”-parameter in Ableton Live.
This scene of 8 faders and 8 knobs is useful for controlling Massive and KORE-based instruments. To my opinion it is more manageable than controlling parameters by endless encoders.
This is a combination of a x-y-pad and a keyboard, especially designed to tweak the FM8 synth while playing. The green buttons in the left corner are for MIDI mapping of the x-y-pad in Ableton Live.