I guess that would be decimal representations of raw midi bytes.
From this website:
0xB0 Continuous Controller
0xC0 Patch Change
0xD0 Channel Pressure
0xE0 Pitch Wheel
0xF0 System Messages
Since hex goes from 0-15 per digit is convenient for midi :)
0x90 note on, channel one
0x91 note on, channel two
0x99 note on, channel ten
0x9A note on, channel eleven
0x9F note on, channel sixteen
that is the other way around of course…
somewhere in the late 70s early 80s some thought:
"since we will be using hex.. this new "midi" protocol will have 16 channels" :)
btw, these messages (note on/off etc) would be the status bytes, describing how the following data should be interpreted. after that comes one or more data bytes.
so, first comes a status byte 0x92. this tells the device that the following data bytes should be interpreted as a note on on channel 3.
then come two data bytes, first the note number and then the velocity. the synth will play on channel 3 this note number with this velocity.