[Linuxsampler-devel] Identical MIDI events cause sound variations?

[Frank N. <bea...@we...>]

Hi list,

I was experimenting a bit with Linuxsampler and sequencer64 yesterday, and
found a little oddity (two, actually): I have loaded a .sfz with a couple of 
synthetic drum samples into LinuxSampler (version LinuxSampler 2.0.0.svn31) 
and send "4-to-the-floor" kick drum MIDI events to it via sequencer64 (output
device from LinuxSampler is JACK).

Though the events are identical with regard to velocity etc, I can clearly
hear that the samples produced by LinuxSampler are varying slight every now and
then in their attack phase. There is roughly 1 "different" (harder, more
direct) kick drum in every 8 or so events.
This is NOT due to some round-robin scheme; there really is only one Kick drum
.wav file assigned to this key.
Also, I observed no JACK xruns while testing this.

This is the corresponding line from the .sfz mapping this kick drum:

<region> sample=..\..\..\wa_drum_tools_01_deluxe\drum kits\deep sleep kit\dt01_kits_deepsleep_kick808.wav lokey=36 hikey=36 end=17616 pitch_keycenter=36 amp_veltrack=71.653542 ampeg_decay=200.199997 ampeg_release=200.199997 pitchlfo_freq=5.000919

That original .wav file is also attached.

I grabbed a short recording via jack_capture and looked at the resulting .wav
in a wave editor; here I clearly see why the sounds really sound different
(see attached pictures: orig_wave.png is the original .wav file, "soft_wave.png"
is one of the (frequent) samples with somewhat softer attack (is there any
AMP envelope applied to every sample at playback?) and "hard_wave.png" is one
of the (more rare) sample playbacks with stronger reproduction of the original
sample's attack phase.

So, there are really two questions in this:
- Why is the playback not giving constantly the same audio output? Could this
  actually be a bug?
- If there is some kind of AMP envelope automatically applied upon each and
  every sample playback (perhaps to avoid the "onset clicks"?), how can I disable
  it to be sure my original sample's playback is authentically reproduced?

Thanks,
Frank