Meaning of values for MIDI control change event

Question

What is the meaning of the two bytes that come at the end of a MIDI control change event?

For eg. I have a MIDI file of Chopin prelude no. 7, and the track for Right Piano has one control change event with values:

tick=956, channel=0, data=[91, 127]

I am interested in knowing what the last two values mean. In this format, they are decimal values of the binary encoded message. What is the significance of the last two bytes?

Answer 1

As the specification tells you, the first data byte is the controller number, and the second byte is the controller value.

As the specification also tells you, controller 91 usually is the reverb send level.