Polyphonic Key Pressure vs Channel Aftertouch
The expressive MIDI pressure specification providing individual pressure sensors per key (status 0xA0) versus global keyboard pressure (status 0xD0).
# Mathematical Formula & Architecture
Logic SpecificationPoly Aftertouch: [0xAn, NoteNumber, PressureValue]. Channel Aftertouch: [0xDn, PressureValue].
# Bandwidth comparison:
# 10-finger chord with active pressure variation:
# Channel Aftertouch: 2 bytes per update (1 global pressure value)
# Poly Aftertouch: 30 bytes per update (10 individual key pressure messages)# Deep Technical Analysis & Historical Context
Most synthesizers implement Channel Aftertouch (status byte 0xD0), where pressing down firmly on any key sends a single global modulation value affecting all sounding voices simultaneously (often mapped to filter opening or vibrato). In contrast, Polyphonic Key Pressure (status byte 0xA0) requires individual conductive elastomer or capacitive pressure sensors beneath every single key on the keyboard bed. This allows a player to sustain a chord and swell the brightness or pitch of only the top melody note without affecting the bass notes. Legendary keyboards featuring polyphonic aftertouch include the Yamaha CS-80, Ensoniq TS-10/EPS, Sequential Prophet-T8, and modern Expressive E Osmose.
Common Studio Pitfall & Hardware Hazard
Transmitting intense polyphonic aftertouch data over a 5-pin DIN cable can consume up to 80% of the 31.25 kbaud wire bandwidth, causing audible timing jitter in MIDI sequencers.
# Frequently Asked Engineering Questions
Why did so few 80s synths have polyphonic aftertouch?
Manufacturing individual pressure sensors and gold-plated contact fingers beneath 61 keys was prohibitively expensive, adding thousands of dollars to instrument retail prices.
Related Engineering Concepts
Back Up Your Hardware Patches Directly in Your Browser
bipluk communicates directly with your 1980s and 90s synthesizers via Web MIDI. Zero driver headaches, automatic checksum calculation, and encrypted cloud preservation.