Some comments regarding the code change:
The last one, the "amplitude detectio active".... Looks OK. I remember I put this line of code thinking it should work but I had some issues with the LEDs not working as expeted and I commented the line. But... if it now works, great.
Regarding the OSC change, I'm a little puzzled here.You changed the system frequency to 8Mhz, but you did not change the TMR1 prescaler, so at the end the timer is running at double speed. Are you getting the notes in the correct octave? I would expect that everything is now one octave low.
On the other hand, I don't see much benefit in increasing the frequency without adding something else, ... you gain some ADC resolution, so you will probably improve something in the higher notes, but that's it.
And, you didn't change most of the delays in the code, so now everything is happening in half of the time. I see you increase a little the delay when detecting amplitude, but only around 25%. This means that now your amplitude detection range is around 15ms... If it works this way, great! But I would expect some issues with pulse and velocity detection for the lower notes because you are not waiting for a full note period.
There are some other delays in the project that control somehow how long to wait until deciding that the note detection failed. These are now half of the time, so you might have issues with notes not detected (too soon)
