[Linuxsampler-devel] LS click/pop investigation

[Mark K. <mar...@co...>]

Hi,
   I sat for a while this afternoon and investigated the clicks and pops
that we are all getting out of LS. As far as I can tell they are (in my
cases) coming from the lack of release samples and not from the attack
envelope as I had hypothesized  earlier.

   To look at this I first set up Pro Tools and recorded audio coming
from both samplers. After that I measured the latency between the MIDI
event in Pro Tools and when audio was recorded from that event in LS.
This is much easier to find based on going from quiet to loud visually.

   Then knowing that latency number I used the Pro Tools scrubber and
searched for clicks and pops in the LS audio stream. When I found them,
I looked for note off events in the MIDI stream and found that they were
always the same latency value ahead of the click and pop. I think this
pretty clearly demonstrates the problem comes from the end of the sample
and not the beginning.

   One other thing I noted was that for an arbitrarily complex MIDI
stream LS is not actually being asked to work very hard without release
samples. In the case of the bounced jazz piano file I have on my server,
while GSt hits a maximum of 96 notes playing at the same time (the limit
of my GSt license) LS never goes above 14 notes due completely to the
lack of the release samples. 

   With this in mind, I think we will likely have another round of
optimization to look at when we do get release samples in the tool as
this would represent nearly 7 timers as much streaming bandwidth to keep
up with GSt. I'm not saying there will be problems, but rather just
trying to show the importance of release samples on stressing the
overall design.

   Keep in mind also that we need to ensure no clicks and pops when we
use a gig file with no release samples. I intend to look this over later
this evening or by tomorrow evening.

   I hope folks find this interesting. If you have any questions or want
me to look at something specific please let me know.

Cheers,
Mark