Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
An Overview of iOS Pianos
AN OVERVIEW OF IOS PIANOS
Perhaps the most successfully emulated instrument in iOS is the piano. It is surprising since the piano sound seems so complex but very good pianos have been modeled with very small footprints, less than a gb. Compare this with the 13 gbs of the mighty Colossus and you can begin to see the variety of instruments available in this category based on size alone. Prices range from $0 (ironically for the number one pick, Salamander) to $50 for the Colossus.
Yet there are several other parameters worth paying close attention to. Sound quality is supreme, and in this area, if you are looking for realism you must consider string resonance, velocity layers, sample rates, mechanical effects like damper noise, pedal noise, etc.
The next and equally important aspect is the playing "feel". This is controlled primarily by the ability to adjust the velocity curve to a place most comfortable for the player. Note that the first place Salamander lacks such an adjustment parameter.
Finally, in terms of the instrument itself, is the ability to adjust the EQ to the players needs. Some pianos have this onboard with factory presets and user preset save capacity. Again, the winner, Salamander offers only five "brightness" presets. and no onboard EQ.
In meeting one's expectations with a virtual piano it is important to understand all keyboard controllers are not equal and this will affect the sound and playing experience. The most authentic "piano" keyboards will have a hammer action, trisensor technology and the ability to interpret as many as 15-17 velocity layers. (salamander has 15). Final items are download times (Colossus takes 13 hours to download. Others vary based on size), Au availability, and probably some stuff I have forgotten to mention.
My own personal favorite is still the Ravenscroft 275, for its high sample rate, relatively small footprint, string resonance, mechanical noises, velocity layers, onboard EQ, velocity curve, reverb, and the ability to save user presets. And it just sounds terrific.