EXS24: convert envelope times with the hardware fourth-power curve#172
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Each EXS24 envelope time is a 0..127 parameter mapping to a maximum of 10
seconds. It was read linearly (parameter / 127 * 10), but the device applies a
fourth-power curve, so short times were greatly overstated - and the attack
stage skipped even the linear scaling, using the raw parameter as seconds
(~12.7x too long on top of that).
Calibrated against Logic reference instruments saved at known envelope times:
parameter : 19 27 53 71 94 127
seconds : 0.005 0.020 0.303 0.977 3.001 10.0
which fit seconds = 10 * (parameter / 127)^4 to within 1%. A 7.5 ms attack
(parameter 21) was read as 1.65 seconds, so plucked/struck instruments faded in
too slowly to be heard (found converting the DSF Planet Earth library to Waldorf
QPAT; hardware-verified). Convert all stages with the curve in the detector and
invert it in the creator so the round-trip stays consistent.
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Problem
Each EXS24 envelope time is a 0..127 parameter (max 10 s), but the detector read it linearly, and the attack stage skipped even that scaling - it used the raw parameter directly as seconds.
Cause
The device applies a fourth-power curve, not linear. Reading linearly overstates short times badly; the raw-attack made it ~12.7× worse again.
Calibration
Reference EXS24 instruments saved in Logic at known envelope times:
fit
seconds = 10 * (parameter / 127)^4to within 1 %.Effect
A 7.5 ms attack (parameter 21) was read as 1.65 s, so plucked/struck instruments faded in too slowly to be heard and appeared silent. Found converting the DSF Planet Earth library to Waldorf QPAT; hardware-verified on an Iridium.
Fix
Convert all envelope stages with the calibrated curve in the detector, and invert it in the creator so the EXS24→EXS24 round-trip stays consistent. (Supersedes the earlier interim commit on this branch, which only made the attack consistent with the other, still-linear stages.)