I could not find any information what is the relation between the AmpEG Release numeric values and actual time in sec/ms. Can anyone enlighten me?
That information is not published in any of the documentation. The AEG (Amplitude Envelope Generator) consists of the following components:
Initial Level
Attack Time
Attack Level
Decay 1 Time
Decay 1 Level
Decay 2 Time
Decay 2 Level
Release Time
These are the parameters that the synth uses to describe what in old analog synthesizers was referred to as the ADSR (Attack-Decay-Sustain-Release). It uses a series of TIME and LEVEL settings to describe the loudness shape of the sound.
In general, the Amplitude EG, Level is the output, minimum to maximum, 0-127. Time is how long it takes to reach the next Level setting, where 0 is immediate, and 127 is a longer time. The Time parameter is not linear. Designed specifically for musical instrument emulations, the time difference is weighted so that its density is greatest in lower values and extremely sparse as you go higher. The Time difference between 56 and 57 is way, way shorter than the time distance between 125 and 126.
AEG is set by ear, not by seconds and milliseconds.
I’m not exactly sure what you are “converting some SFZ” (is that a file format?) or are you trying to recreate a sforzando articulation (?) Sorry this is not clear from your post.
Let us know... MODX offers some unique methods to emulate the musical gesture Sforzando (none of which requires a stop watch or a chart!)
You can automate it, you can setup for manual control, you can work in realistic timbre change along with the amplitude change.
The brass swells and sforzando gesture emulation on this engine break some new ground...imho