An extension to the MIDI standard, adopted in 2010, to extend the range of possible velocity values in a Note On message. The standard Note On message has one byte for velocity, allowing for 7 bits of precision, or 127 possible values. The high resolution velocity prefix involves sending a Continuous controller message, using controller number 88, prior to the note on. It provides an additional 7 bits of precision for the velocity value; the prefix message provides the low-order 7 bits, and the conventional velocity field in the Note On message provides the high order 7 bits. Per the standard, the prefix message effects only the first following Note On. Sound sources that do not recognize controller 88 as a defined controller will simply ignore it.
As of January 2012, the only MIDI keyboard on the market that transmits High Resolution Velocity Prefix messages is the VAX-77 master keyboard from Infinite Response. It is used mainly with soft synths that create piano sounds.
The CASIO PX5S and PX-560 also transmit MIDI CC#58h.