Filter keytrack at 100% makes filter cutoff follow note pitch harmonically, preserving timbre across the keyboard

Filter Keytrack in Surge XT controls how much the played note’s pitch shifts the filter cutoff frequency. At 0% keytrack, the cutoff is fixed regardless of which note is played — high notes become progressively duller because their overtones pass through the filter less than lower notes. At 100% keytrack, the filter cutoff moves in exact proportion to the note pitch, keeping the harmonic relationship between the fundamental and the cutoff constant. This preserves the same timbre across the keyboard, exactly as an acoustic instrument’s resonant character scales with pitch. Partial keytrack values (e.g., 50%) provide a compromise. In Surge XT, the Keytrack Root Key sets the note at which keytrack modulation is zero — notes above are positive, below are negative.

Examples

A pad with filter cutoff at 800 Hz and 0% keytrack will sound muddy on high notes and harsh/dull on low ones. Set keytrack to 100% and tune the cutoff to taste at the root key for even timbre.

Assessment

A synth patch sounds progressively duller on higher notes but vivid on lower ones. What single parameter change would you make and why? What keytrack percentage would you set for a timbre that gets slightly brighter at higher pitches but not as much as full tracking?