Velocity and Aftertouch
Velocity sits in the second Note On byte, while aftertouch adds pressure held after the key.
Related
Soft and hard presses are often treated as quiet and loud. Aftertouch is missed, though pressure under the finger can travel as its own message.
The problem
The piano roll draws velocity bars while the fader moves volume; mixing them flattens expression. A string note that refuses to change often lacks aftertouch, not a better patch.
Protocol or message
Note On uses 0x9n with key and velocity from 1 to 127, where 0 means Note Off. Channel pressure is 0xDn with one byte and affects the whole channel. Polyphonic aftertouch is 0xAn with key and pressure, affecting one note. Velocity is sent at the attack, while aftertouch can stream. Drum tracks use poly aftertouch to choke cymbals.
Settings and practice
Keep piano velocity inside 20 to 110 with headroom. Shape a long string note with channel pressure, or per-note pressure under MPE. Set velocity layers in the sampler, or the value changes only level. Calibrate the aftertouch curve on the keyboard, not the default.
What to listen for
A velocity gap above twenty moves the accents. Aftertouch lets a held note keep changing, like a vibrato that deepens, while choke aftertouch cuts a cymbal short.
Common misunderstandings
Velocity is not volume, as a sampler may map it to brightness or a layer. Aftertouch is not pitch bend. A keyboard without aftertouch can fake some expression with CC1.
Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- MIDI 1.0 规范对 Note On 力度与两类触后的定义，依 MMA 公开规范核查，未抄文本
- 本库 C1 文件的力度分布与复音触后统计，由本地 SMF 解析脚本核对，数值随文件而定
Used for fact-checking only; all prose is original.