I opened up one of those PDF files that's been in the document folder for-what and for-how-long, I know not. A couple of clicks later I'm looking at a document titled "TEN ORGAN PRELUDES for Liturgical Services" by John Lee. (Who knew someone other than Bach wrote preludes).  #4 was chosen for entry into the MIDI Music System software to get a feel for making volume and tempo changes.

The Yamaha TG-33 has been feeling a little bit neglected lately, hence the effort to use it for this composition.  As we know, not all synthesizers are created equal, the MIDI Implementation Chart is a good place to find out which controls are available.  The TG-33 has 7 controls that can be changed by typing "Pn,val" into MMS.

n

0 = Bank Select MSB

1 = Modulation Wheel

7 = Volume

16 = Vector X

17 = Vector Y

32 = 32 Bank Select LSB

64 = Sustain

There is also the Velocity that gets sent with each NoteOn command that might affect the volume.  It does on some, but the Factory Organ patches didn't respond to velocity changes, but then again, the organ patch on CARD VC3301 STAGE volume changed.  A Velocity change would have to be made in each Voice. The Volume control (7) seemed the better option.

NUM04.atr   NUM04.MUS

The volume controller sets the volume on all notes on the MIDI channel. The MMS Voices 1 - 4 hold the music's note data.  Voice 5 makes the tempo and volume change.  Rests are used for timing. All five Voices are set to channel 1 for playback. 

Audacity was used for recording. After upgrading, it took me about a day to figure out that permission had to be set to allow access to the sound digitizer. But that's another story.