I appreciate your insight Grumpy_Mike. I've learned from a dozen or so forum posts with your feedback while writing my code, thanks.
I currently have a Serial.begin(9600); in the setup.
Not sure if this is possible but I think a SoftSerial.begin(31250); is also defined in the library I'm using.
I'm using the CC data from an expression pedal to scrub through some scales associated with the chords the synth is playing. The synth has 4 note polyphony so i'm using 3 notes for chords and the last one for kind of a randomized solo I can scrub while playing. And to be clear, the CC messages, and clock are coming from an external device, to the arduino, then out to a synth.
I took your advice and tried to boil down my code as far as possible, always good advice... and was able to make that work as desired. Aka, a note sequence is playing over time, and a second note is played with it, as defined by the expression pedal.
I found a couple things:
-
I was getting some outlier CC data from my expression pedal. Because I'm calling the "MIDI.GetType2()" to pull the CC data, I was pulling some things I didn't want. I didn't see this initially. Usually the CC data would be in the range I was asking for, but occasionally I would get some number above 127. I will try clamping that so those outliers don't get out, or call the CC data differently.
-
I could see how much the Serial.printing of the expression pedal CC data was adding latency in the serial monitor.
I currently trying to apply this concept to my current full sketch, without any luck.
I do have a fair amount of Serial printing happening, giving me readouts of note numbers/velocity, tempo ticks and the like. Perhaps cutting down on that would help?
I will see if I can unclog whats happening with the Serial information, and report back. In the meantime let me know if there's anything in what I just said that seems suspect. 
Thanks.
The below code is like a very basic version of what I'm looking for, and appears to be working:
#include <SoftwareSerial.h>
#include <MsTimer2.h>
#include <MIDI.h>
#define PIN_LED_PLAYING 6
#define PIN_LED_TEMPO 7
#define PIN_PLAY_INPUT 2
#define PIN_CONTINUE_INPUT 3
SoftwareSerial SoftSerial(8, 9);
MIDI_CREATE_INSTANCE(SoftwareSerial, SoftSerial, MIDI);
int ticks = 0;
const int song01[] = {45, 46, 47, 48, 49, 50, 51, 52}; //midi note numbers
int note1 = 0;
int prevnote1 = 0;
int note2 = 0;
int prevnote2 = 0;
int songStep = 0;
int playflag1 = 0;
int crazyNote = 0;
void setup() {
//tempo visual LEDS
pinMode(PIN_LED_PLAYING, OUTPUT);
pinMode(PIN_LED_TEMPO, OUTPUT);
digitalWrite(PIN_LED_PLAYING, HIGH);
digitalWrite(PIN_LED_TEMPO, HIGH);
Serial.begin(9600);
//the below comments are from the library example sketch
//SoftSerial.begin(31250);
// do I need to init the soft serial port?
// No - MIDI will do it.
#if 1
MIDI.begin();
//MIDI.setHandleControlChange(myCCfunction);
MIDI.turnThruOff();
#endif
}
void loop() {
//these three values I'm not sure if I need, copied from other code//
static uint32_t loops = 0;
static uint8_t ticks = 0;
static uint8_t prev_ticks = 0;
//define note numbers
note1 = song01[songStep];
note2 = crazyNote;
//note player
if (playflag1 == 1) {
//turn off if new note values are different
if (prevnote1 != note1 || prevnote2 != note2) {
MIDI.sendNoteOff(prevnote1, 0, 1);
MIDI.sendNoteOff(prevnote2, 0, 1);
}
MIDI.sendNoteOn(note1, 127, 1);
MIDI.sendNoteOn(note2, 127, 1);
prevnote1 = note1;
prevnote2 = note2;
playflag1 = 0; //set note player to off when note has played
}
if ( MIDI.read())
{
switch (MIDI.getType())
{
case midi::Clock: //driven by external midi clock
MIDI.sendRealTime(MIDI_NAMESPACE::Clock); //send to external synth for visualization of tempo
ticks ++;
Serial.print('.');
Serial.println(ticks);
if (ticks < 6)
{
digitalWrite(PIN_LED_TEMPO, LOW); //tempo LED flash
}
if (ticks == 6)
{
digitalWrite(PIN_LED_TEMPO, HIGH); //tempo LED flash
}
if (ticks >= 24)
{
ticks = 0;
songStep++;
Serial.print("SONGSTEP = ");
Serial.println(songStep);
playflag1 = 1;
}
break;
case midi::Start:
playflag1 = 1; //start note player
break;
case midi::Stop:
playflag1 = 0; //stop note player
break;
case midi::ControlChange:
//get CC value of expression pedal output
crazyNote = MIDI.getData2(); //CC number = 1, value = 50-62, channel = 1
//Serial.print("crazyNote = ");Serial.println(crazyNote); //lag if on
break;
default:
break;
}
}
if (songStep >= 7) {
songStep = 0; //reset song note array
}
}