For anyone wishing to play GarageBand (iOS) instruments sounds, below is a helpful list for controlling instrument sound parameters.

To use GarageBand (iOS), you will need to put the GarageBand app into background mode.

   MIDI CC 1:  bowing to pizziccato
   MIDI CC 7:  track volume
   MIDI CC 10: pan
   MIDI CC 11: instrument volume (adjust instrument level without affecting volume of effects)
   MIDI CC 64: sustain (anything above 0 will hold notes until next 0 value)
   
   Responds to note velocity
   Responds to pitch bend, but the pitchbend range is set to 0 by default
   no volume control for individual strings
   no response to polypressure
   no response to channel pressure
   
   Instruments (based on note pitch value):
   21-35 Bass
   36-47 Cello
   48-60  Viola
   61-108 Violins
   
   Default values for strings:
   MIDI CC: 1 value: 0
   MIDI CC: 7 value: 127
   MIDI CC: 10 value: 63
   MIDI CC: 11 value: 127
   MIDI CC: 64 value: 0

Below is the standard reset parameters command, however iOS garageband does not seems to respond to this:

      MIDI CC: 121 value: 0

   MIDI CC 1:  vibrato or mod effect
   MIDI CC 7:  track volume
   MIDI CC 10: pan
   MIDI CC 11: instrument volume (adjust instrument level without affecting volume of effects)
   Responds to pitchbend
   Polypressure and channel pressure active and seem to target a modulatory variable (the same one). 
   Input targets differ with each preset. 
   Eg channel pressure sometimes used for mod effect, sometimes used for vibrato. 
   Some pads use channel pressure to control the rate of rhythm effects. 
   If one of the *dial parameters* is being controlled by channel pressure, midi control starts from where the dial 
   is set.

   MIDI CC 1:  muted to rung out
   MIDI CC 7:  track volume
   MIDI CC 10: pan
   Responds to pitchbend
   Lower octaves play chords (chords are not sensitive to note velocity)
   All sound vary their sound depending on note on velocities lower, except for 'hardrock'
   no response to poly- or channelpressure