EXS24: convert envelope times with the hardware fourth-power curve

documentation/CHANGELOG.md

@@ -24,6 +24,7 @@
   * Fixed: A mapping slot without explicit sample-trim points read a sample start and end of -1 instead of the whole sample (e.g. a converted Waldorf QPAT then showed a sample start and end of -1 on the device).
 * EXS24
   * Fixed: Loop type was not applied.
+  * Fixed: Envelope times were converted from the EXS24 parameter linearly, but the device applies a fourth-power curve, so short times were greatly overstated - and the attack stage additionally skipped even the linear scaling, coming out about 12.7 times too long on top of that. A quick attack (e.g. 7.5 ms) was read as over a second, so plucked and struck instruments faded in too slowly to be heard and appeared silent. Envelope times are now converted with the hardware-calibrated curve seconds = 10 * (parameter / 127)^4, matching Logic to within one percent (thanks to Douglas Carmichael).
 * FLAC/OGG
   * Fixed: FLAC or OGG samples stored inside a ZIP archive (e.g. discoDSP Bliss or DecentSampler libraries) could fail to decompress.
   * Fixed: Stereo (multi-channel) samples stored in a compressed format were truncated to half their length when decompressed while writing to an uncompressed destination.

src/main/java/de/mossgrabers/convertwithmoss/format/exs/EXS24Creator.java

@@ -288,8 +288,12 @@ private static void applyFilterParameters (final EXS24Parameters parameters, fin
 
     private static int formatEnvTime (final double time)
     {
-        // Maximum time for each step are 10 seconds
-        return time < 0 ? 0 : (int) Math.round (time / 10.0 * 127.0);
+        // The device maps the 0..127 parameter to a maximum of 10 seconds with a fourth-power
+        // curve (see EXS24Detector.envelopeTimeToSeconds), so invert it:
+        // parameter = 127 * (seconds / 10) ^ (1/4).
+        if (time <= 0)
+            return 0;
+        return (int) Math.round (127.0 * Math.pow (Math.min (time, 10.0) / 10.0, 0.25));
     }
 
 

src/main/java/de/mossgrabers/convertwithmoss/format/exs/EXS24Detector.java

@@ -338,13 +338,12 @@ private static IEnvelope createEnvelope (final EXS24Parameters parameters, final
         final Integer attackCurve = parameters.get (envelopeIndex == 1 ? EXS24Parameters.ENV1_ATK_CURVE : EXS24Parameters.ENV2_ATK_CURVE);
 
         final IEnvelope envelope = new DefaultEnvelope ();
-        // Maximum time for each step are 10 seconds
-        envelope.setDelayTime (delay == null ? 0 : delay.doubleValue () / 127.0 * 10.0);
-        envelope.setAttackTime (attack == null ? 0 : attack.intValue ());
-        envelope.setHoldTime (hold == null ? 0 : hold.doubleValue () / 127.0 * 10.0);
-        envelope.setDecayTime (decay == null ? 0 : decay.doubleValue () / 127.0 * 10.0);
+        envelope.setDelayTime (envelopeTimeToSeconds (delay));
+        envelope.setAttackTime (envelopeTimeToSeconds (attack));
+        envelope.setHoldTime (envelopeTimeToSeconds (hold));
+        envelope.setDecayTime (envelopeTimeToSeconds (decay));
         envelope.setSustainLevel (sustain == null ? 1.0 : sustain.doubleValue () / 127.0);
-        envelope.setReleaseTime (release == null ? 0 : release.doubleValue () / 127.0 * 10.0);
+        envelope.setReleaseTime (envelopeTimeToSeconds (release));
 
         if (attackCurve != null)
         {
@@ -358,6 +357,27 @@ private static IEnvelope createEnvelope (final EXS24Parameters parameters, final
     }
 
 
+    /**
+     * Convert an EXS24 envelope time parameter to seconds. The parameter ranges from 0 to 127 and
+     * maps to a maximum of 10 seconds, but the device applies a fourth-power (not linear) curve, so
+     * low values are far shorter than a linear reading suggests. Calibrated against Logic reference
+     * instruments (parameter 19 = 5 ms, 27 = 20 ms, 53 = 303 ms, 71 = 977 ms, 94 = 3 s, 127 = 10 s),
+     * which fit seconds = 10 * (parameter / 127)^4 to within 1 percent. Reading these times linearly
+     * made e.g. a 7.5 ms attack come out as 1.65 seconds, so the note faded in too slowly to be
+     * heard.
+     *
+     * @param parameter The raw envelope time parameter (0..127), or null when not present
+     * @return The time in seconds
+     */
+    private static double envelopeTimeToSeconds (final Integer parameter)
+    {
+        if (parameter == null)
+            return 0;
+        final double normalized = parameter.doubleValue () / 127.0;
+        return 10.0 * normalized * normalized * normalized * normalized;
+    }
+
+
     private static void applyFilterParameters (final IMultisampleSource multisampleSource, final EXS24Parameters parameters)
     {
         final Integer isFilterEnabled = parameters.get (EXS24Parameters.FILTER1_TOGGLE);