Category: Voice
Purpose
Indicates that a particular note should be played. Essentially, this means that the note starts sounding, but some patches might have a long VCA attack time that needs to slowly fade the sound in. In any case, this message indicates that a particular note should start playing (unless the velocity is 0, in which case, you really have a Note Off). If the device is a MultiTimbral unit, then each one of its Parts may sound Note Ons on its own channel. The Part that sounds a particular Note On message is the one assigned to the message's MIDI channel.
Status
0x90 to 0x9F where the low nibble is the MIDI channel.
Data
Two data bytes follow the Status.
The first data is the note number. There are 128 possible notes on a MIDI device, numbered 0 to 127 (where Middle C is note number 60). This indicates which note should be played.
The second data byte is the velocity, a value from 0 to 127. This indicates with how much force the note should be played (where 127 is the most force). It's up to a MIDI device how it uses velocity information. Often velocity is be used to tailor the VCA attack time and/or attack level (and therefore the overall volume of the note). MIDI devices that can generate Note On messages, but don't implement velocity features, will transmit Note On messages with a preset velocity of 64.
A Note On message that has a velocity of 0 is considered to actually be a Note Off message, and the respective note is therefore released. See the Note Off entry for a description of such. This "trick" was created in order to take advantage of running status.
A device that recognizes MIDI Note On messages must be able to recognize both a real Note Off as well as a Note On with 0 velocity (as a Note Off). There are many devices that generate real Note Offs, and many other devices that use Note On with 0 velocity as a substitute.
Errata
In theory, every Note On should eventually be followed by a respective Note Off message (ie, when it's time to stop the note from sounding). Even if the note's sound fades out (due to some VCA envelope decay) before a Note Off for this note is received, at some later point a Note Off should be received. For example, if a MIDI device receives the following Note On:
0x90 0x3C 0x40 Note On/chan 0, Middle C, velocity could be anything except 0Then, a respective Note Off should subsequently be received at some time, as so:
0x80 0x3C 0x40 Note Off/chan 0, Middle C, velocity could be anythingInstead of the above Note Off, a Note On with 0 velocity could be substituted as so:
0x90 0x3C 0x00 Really a Note Off/chan 0, Middle C, velocity must be 0If a device receives a Note On for a note (number) that is already playing (ie, hasn't been turned off yet), it the device's decision whether to layer another "voice" playing the same pitch, or cut off the voice playing the preceding note of that same pitch in order to "retrigger" that note.