Volume slider not working in soft synth ?

I installed a soft synth into a project - z3ta+.   

In the "Insert Soft Synth" options, I checked Midi Source, Synth Track folder, and First Synth Audio output.

I recorded some notes on the z3ta+ Midi track.  When playing it back the volume slider on that track did not work, but volume can be controlled on the Midi source track (I think its that way round ?  I recorded on the track with the icon like the end of a Midi cable, and the track where the volume can be changed has an icon looks like a Midi cable over a small keyboard ...).

I did the exact same with Omnisphere on another track, but on that instance I could adjust the volume on the track with the Midi icon.

Confused ........ what's right?  And what's the difference?

The volume slider in the MIDI track sends CC7 MIDI volume controller messages. I just checked, and the Master volume in z3ta+ responds to it as expected (some synths don't, or don't have a volume fader that clearly shows the response - e.g. Dim Pro).

The volume slider in the instrument track (i.e. an audio track with a soft synth assigned as input) controls the output level of the audio from the track. When it's at 0dB, the output level will be the same as the input level coming from the synth.

It's generally best to set the MIDI volume to some fixed value that gives a good output level from the synth without driving the input level of the track too hard, and then control the mix volume with the audio/instrument track volume. But both should have an effect.

The effect of velocity on volume is a different deal. The "Gain" control in the MIDI track applies an offset to the velocities embedded in the individual notes. Many z3ta+ patches do not respond to velocity by default, so changing the MIDI Gain (a.k.a. Vel+) would have no effect.

P.S. To add velocity response to a z3ta+ patch that doesn't have it, go to the Modulation section at the bottom of the z3ta+ GUI, and set the following values for Source, Range, Curve, Control and Destination: 


ON     |||||||||||||||||||||||||     U-Lin+     VELOC     ALL OSC LEVEL    

P.P.S. I should clarify that when I say "velocity response", I mean change in volume with changing velocity. Velocity can also affect other sound parameters like LFO depth/frequency, filter envelopes, pitch envelopes, etc., and many z3ta patches do respond to velocity in that way.