Many synths provide an ‘AMP Velocity %’ control (0 to 100%) which scales the amp-adsr control signal (that controls the VCA). Providing the following behaviour (assuming a linear curve) :
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At 0%, notes play at max VCA level, irrespective of the velocity value.
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At 100% (full dynamic range) :
velocity = 127 : produces a note at max VCA level
velocity = 1 : produces a note at min (non-zero) VCA level
velocity = 64 : produces a note at ~50% VCA level -
At 50% :
velocity = 127 : produces a note at max VCA level
velocity = 1 : produces a note at 50% VCA level
velocity = 64 : produces a note at ~75% VCA level
And so on. Essentially, as the % velocity sensitivity is increased, the dynamic range extends downwards from the max VCA value. For the maths oriented it’s (in C) :
envMultiplier = (vel == 0) ? 0 : 1 - ((1 - vel / 127) * sens / 100);
Can this behaviour be achieved with the A4 ?
AIUI the current implementation (Sound Settings > Velocity to Vol) provides the two extremes (0% and 100%) but not the variable sensitivity I’m looking for. The exp/log curves don’t help here, as the end-points are unchanged, i.e. a velocity of 1 gives an almost inaudible note, whilst a velocity of 127 gives a note at max volume, and this is true whatever curve is selected.
Also, I’ve had no success with Sound Settings > Velocity Mod, e.g. controlling the AMP Volume.
In case anyone’s wondering ‘why?’. I don’t want notes played at very low velocity to be virtually inaudible. 
Lenny.