Usually for live performance very convenient use the MIDI controller for control the audio processing apps or simple MIDI keyboard for synthesizer apps. For the best audio preferable to use an external audio interface connected to the iOS device. With MIDI controller and audio interface you can conveniently use apps for live performance even on iPhone.
To connect several USB MIDI and audio devices to single iPad or iPhone you can use simple non-powered USB hub. Mostly any hub works without problems. But in this case you should use power adapters for your MIDI controllers and audio interfaces. Or you can use powered hub and connect to him any controller that can powering thru USB.
Also you need have "Lightning to USB Camera Adapter" to connect USB hub to the iOS device:
Lightning to USB Camera Adapter (with this adapter iOS device will powering from battery)
Lightning to USB 3 Camera Adapter (this adapter can power and charge iOS device)
In this setup were used two apps SynthScaper and FieldScaper on iPads, three DIY sound boxes and analog synthesizer with two analog effect units.
Click on image to enlarge
The SynthScaper app was controlled by a MIDI keyboard/controller Akai MPK49, and FieldScaper app by MIDI controller Novation Zero MKII. Each iPad with own app was connected to individual audio interface Focusrite Scarlett 6i6. Stereo outputs from these interfaces were mixing and recording on Tascam Portastudio 424 Mk III. Of course it could be any other mixer and recorder. Also to the mixer was connected separate mono audio output from synthesizer Roland Juno-60 processed thru filter Akai MFC42 and tape delay Roland RE-201 Space echo.
Outputs from DIY sound boxes were connected to external audio interface of FieldScaper app. The FieldScaper processed sound from these devices in real time with the first oscillator in the "Loop" mode, and also plays and processed several pre-recorded loops in the second and third oscillators.
This setup in action:
[ More about SynthScaper - Soundscapes synthesizer ]
[ More about FieldScaper - Field recorder & Scapes constructor ]
There is another setup with SynthScaper and SoundScaper apps.
In this example different oscillators in SynthScaper control by external MIDI sequencer Doepfer Dark Time and MIDI keyboard/controller Akai MPK49. The SoundScaper app was operated by MIDI controller Korg nanoKontrol2. Two stereo outputs from external audio interfaces Focusrite Scarlett 6i6 were mixed and recorded on Tascam Portastudio 424 Mk III.
Click on image to enlarge
All USB devices (except Korg nanoKontrol2) have own power supplies and connected to iPads thru non-powered USB hubs. Korg nanoKontrol2 powering from iPad battery thru USB hub.
This setup in action:
[ More about SynthScaper - Soundscapes synthesizer ]
[ More about SoundScaper - An experimental sound mini lab ]
Two synthesizers processed by FieldScaper app.
In this example two synthesizers - Roland Juno-60 with additional effect unit Roland RE-201 Space echo and Korg MS2000 were used as external audio sources for first oscillator in FieldScaper app. This oscillator was configured in "Looper" - "Effect" mode. Synthesizers were connected to two different input channels of external audio interface Focusrite Scarlett 6i6. In the app these channels mixed to one for use in oscillator. For this oscillator was used the slightly modified preset "Dark and foreboding places".
Two other oscillators in FieldScaper app were configured for using pre-recorded samples with several presets. All oscillators were operated by using MIDI controller Novation Zero MKII. The six faders at the right side are assigned on "Main effect" and "Output level" for each oscillator. Buttons below assigned for switch between presets and samples. Knobs at the left side are assigned for mixer "Distance" / "Panorama", filter "Frequency" / "Resonance" and for "Clock" / "Clock offset".
Click on image to enlarge
Stereo output from FieldScaper app thru external audio interface was recorded on Roland V-Studio 100.
This setup in action:
[ More about FieldScaper - Field recorder & Scapes constructor ]