The app formerly known as AlephOne, this is my current app that I am working on.
It is under active development, and was recently submitted to the App store, and is awaiting review.
The main thing about it is moveable frets for better microtonality, legato behavior in the MIDI is better.
The sound engine doesn't have a lot of variety currently, but it behaves really well with respect to aliasing/impulsing issues, for an organic analog-like sound.
It is however a much more minimal instrument than Geo Synthesizer.
Please read this about the MIDI:
An Ideal MIDI Protocol
as the pitch bending cannot be handled in one MIDI channel. You can use SampleWiz or ThumbJam (in Omni mode) to get the correct kind of pitch behavior. Otherwise, if you mash the MIDI back to 1 channel, just know that it's not possible for MIDI to render it correctly (this is a problem that can only be fixed by using something other than MIDI).
iPad/iPhone App: Geo Synthesizer
The Official Geo Synthesizer Site may be of use to you.
This app is a collaboration with Dream Theater's Jordan Rudess and Kevin Chartier (authors of MorphWiz and SampleWiz).
Geo Synthesizer has been in the store for about a half year under Wizdom music.
It is geared towards more normal use cases than Mugician, and it specifically has support for MIDI and importing SampleWiz samples; and even playing both of these sound engines simultaneously.
The first use of octave automation is in Geo.
I get reports from users that Geo is used extensively in the real world in a live setting.
It costs $9.99, and has gotten good reviews in spite of it deliberately being a bit of a specialty item.
iPad App: Mugician
This was my first iPad app. It's a free app in the store, first released and last updated almost two years ago.
It spent a year in the top 100 free music apps in spite of being a microtonal instrument (making it an esoteric specialty).
It is popular among guitar players because it has low latency and a layout that guitarists can play fast on without a lot of practice beforehand.
AlephOne v0.0.71 - Much rebalancing, and changed looping button look to guide user into figuring it out.
AlephOne v0.0.70 - Some rebalancing to keep sine wave from clipping too much, changed looper into feed/mix for easier control.
AlephOne v0.0.69 - Looping behavior improved for the case where you just want a timed delay. Just do 3..4..1.. with no playing in between and it will pick it out for you.
AlephOne v0.0.68 - Fixed balance and clipping issues. Looper behavior still a little unsatisfactory (still at it).
AlephOne v0.0.67 - Instability created by using looper multiple times seems to be taken care of.
AlephOne v0.0.65 - Looper and Long delay added. In time (..1..2..3...4.. ..) Hit loop on 3 to give a reference time, hit countin on 4, then play on 1 (ie: 1..2..3..4..1..). When you are on the last note of the loop, hit loop again, and it will immediately loop. Timing should be exact.
AlephOne v0.0.54 - Starting a rewrite of the ramping to avoid impulsing and include attack/decay (no controls for it yet).
AlephOne v0.0.53 - There was a major audio bug that caused previous sound from 47-51 to sound very wrong. I also purged almost all devices, so you will need to send me an email to re-request access to it. Re-send me the UDID for the device that you use.
AlephOne v0.0.50 - Very experimental build, just made to add some people to the profile. If you can install older builds, you might have to to back to 49.
AlephOne v0.0.49 - Experimental vDSP build part 2. Same as 48 except aliasing at higher frequencies is handled better.
AlephOne v0.0.48 - Experimental parallel vDSP build. Retreat to v0.0.47 if there is anything wrong with this one.
AlephOne v0.0.43 - Included an echo, got rid of MIDI based chorusing and just put chorusing effect into the internal engine. There are no controls for internal engine yet (as the controls will have to ride over MIDI in addition to simply needing user interface elements.)
AlephOne v0.0.42 - Put pressure sense fully back in. If Orphion is doing it now, then I am confident that I will be able to ship like this as well.
AlephOne v0.0.41 - Got rid of stuck note issue inNRPN (probably... it needs lots of testing to be sure!)
AlephOne v0.0.39 - Added actual legato in polyphony mode. Sound cleaned up a bit more. But there is still a stuck note issue (you can pretty easily clear it by playing fast, but it definitely can happen.)
AlephOne v0.0.38 - Internal engine cleaned up a bit. A credible organ sound is emerging.
AlephOne v0.0.37 - Internal engine is in reasonable shape. There is still impulsing on start/stop and you need to run this through a good external reverb at the moment. Dial down the velocity a little bit for more expression.
AlephOne v0.0.36 - Fixed a hammer-off bug found by Okay Cihaner. Arbitrary microtonal hammeroffs should come out at right pitch, and will resend bend value on note-up no matter what now (even if it's redundant technically). (Give me feedback if it isn't fixed).
AlephOne v0.0.35 - Actual fretlessness is now supported again, with a lighter type of pitch geometry that's similar to the one in Geo.
AlephOne v0.0.34 - Fix problem with drawing all frets when there are many rows (reducing memory use to do this).
AlephOne v0.0.33 - Fix stability issues, and added in the major micro scales as examples. (Just kind of play them like normal diatonic scales locating by the note names, and it's mostly an issue with chord timbre and doesn't have to sound wierd.)
AlephOne v0.0.32 - More work on the scale editor. The scales edited are the ones you can switch between. Changing root via circle of fifths determines location of center of the scale now.
AlephOne v0.0.31 - Added some aggressive MIDI changes. It sends channel pressure messages that track current volume so that if you manipulate volume, the MIDI can potentially respond to the change. (If I get a synth properly changing volume during legato and responding to this, then it makes sense to put finger-area sense back in now.)
AlephOne v0.0.30 - Added in a rudimentary microtonal capable scale editor. I am going the route of picking out notes from the common spots in rings of equal temperments (7,12,19,24,31,53,106), where 106 could serve as a Pythagorean/Arabic/Diatonic master scale, but the others are in there because they are so commonly used. I am not sure how I would support actual ratios. For the near future, it will probably simply display the highlighted location in cents.
AlephOne v0.0.29 - Put in a polyphony switch to go from solo mode, string mode, to full poly mode.
AlephOne v0.0.28 - Put in an explicit volume slider, without it being dominated by aftertouch, the finger-area sense is just far too jumpy.
AlephOne v0.0.27 - I had to re-order CC with note-down to preven CC from being wrong on the attack moment. I hope it didn't break things, as this was a very tricky thing to do. But it didn't confuse the synths I tried so far.
AlephOne v0.0.26 - I don't remember what went into 26. I forgot to add it.
AlephOne v0.0.24 - Put in CC#11 on y axis, especially for if you have to disable chorus. Put in numeric labels for the MIDI settings.
AlephOne v0.0.23 - Support interface re-orientation. It's really necessary for Alesis dock.
AlephOne v0.0.22 - Performance fix, lots of visual enhancements.
AlephOne v0.0.21 - Added switch for octave rounding, white key markers.
AlephOne v0.0.20 - Fixed bugs against stock MIDI synths (ie: euphemism for impls that just suck!)
AlephOne v0.0.19 - Added in control over important MIDI parameters. Channel base, channel span (cycling control), and pitch bend width are now controllable, though a little rough at this time.
AlephOne v0.0.18 - Got control paging, and enough controls to be useful added. Only tested on phone right now. But I have gotten to the point where adding all the simple controls is as easy as it can be now.
AlephOne v0.0.17 - Sliders are labeled, more invisible structural changes.
AlephOne v0.0.15 - Disable fully fretless until I can get all bugs out of it. Highest intonation setting is a simple Just Intonation minor scale.
AlephOne v0.0.14 - Got first controls, and using one for scale pick, one for center, and one for width to get a sort of multi-line Morphwiz layout.
AlephOne v0.0.13 - Backtracked on some of the goofy texturemap graphics, and a bunch of internal changes to get me closer to having controls (it will happen all at once when I get there).
AlephOne v0.0.10 - Make color scheme much more legible. Move the channel representation off to the corner a bit (it will be a control when in control mode at some point).
AlephOne v0.0.9 - Got it running on my iPad running iOS 4.2.
AlephOne v0.0.8 - Added in a visualization of channel cycling and our bending trickery, have handles to let us change the base/span at some point, need handles to change bend range.
AlephOne v0.0.7 - Major ui changes to keep a histogram of recent fret usage to highlight hotspots in the octave. Also fixed pitch rounding speed issues so that it's the same speed going up and down.
AlephOne v0.0.6 - Support for prioritized frets, expressivity fixes, and algorithm fixes for when columns/rows, etc are moved around. Added accelerometer velocity and finger area sense for now. Use this with ThumbJam's violin(!!).
AlephOne v0.0.5 - Put the chorusing back in, which required fixing some pitch snapping over time issues (tick), cleaned up issues with coordinate system inconsistencies.
AlephOne v0.0.4 - Added in moveable frets. It's setup now to have all chromatics plus E,B,A quartersharp as well. This is Arabic scale convention (kind of...with intervals adjusted to Just intonation if they can). The point of it is that you can play the minor third interval that straddles the quartertone, where the quartertone is in the dead center of it.
What is it? Get ThumbJam 2.0, and run it with background audio turned on, Omni mode enabled and the JR Zendrix sound. Then launch AlephOne. Its playing interface is basically Geo (fretless, 3 strings, 5 frets). It gets a lot more of the MIDI right, and should ultimately be far more stable than Geo due to being simpler (though right now, it's under development, so that is something that comes and goes).
AlephOne is a reference to the infinite set theory of
Georg Cantor.
A video of it in use in its current state is here: