MIDI keyboard controlled LED strip
The biggest problem is that updating the LEDs is an intensive task.


Hand-crafted assembly is written to get the timing right
Interrupts are disabled while the update is running
88 LEDs take a (relatively) long time to update.


At about 1.2µS per LED plus 50µS for the reset pulse, you're looking at about 155µS that the Arduino can't be doing anything else at all. That includes receiving anything through serial.  And since you update for every note you receive, if there is a second note coming in with 155µS of that one, it will be missed.

You may get better results with the FastLED library instead of the Adafruit Neopixel library, but ideally you want to work with a board that is fast enough to not need to do such tight bit-banging for the protocol, so that interrupts can still be enabled for receiving data.