Do exactly this and tell us what happens:

1) killall -9 jackdbus jackd # and kill any other sound-hogging application
2) jackd -dalsa
3) rakarrack

output on preset "Rodent Airlines" :

jackdmp 1.9.7
Copyright 2001-2005 Paul Davis and others.
Copyright 2004-2011 Grame.
jackdmp comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
no message buffer overruns
no message buffer overruns
JACK server starting in realtime mode with priority 10
control device hw:0
control device hw:0
audio_reservation_init
Acquire audio card Audio0
creating alsa driver ... hw:0|hw:0|1024|2|48000|0|0|nomon|swmeter|-|32bit
control device hw:0
configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 2 periods
ALSA: final selected sample format for capture: 16bit little-endian
ALSA: use 2 periods for capture
ALSA: final selected sample format for playback: 16bit little-endian
ALSA: use 2 periods for playback
JackEngine::XRun: client = rakarrack was not run: state = 2
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 1
JackAudioDriver::ProcessGraphAsync: Process error

for "Edgy", "Satriani" for instance the output is practically the same but end integer is 2:

JackEngine::XRun: client = rakarrack was not run: state = 2
JackAudioDriver::ProcessGraphAsync: Process error
JackEngine::XRun: client = rakarrack was not run: state = 2
JackAudioDriver::ProcessGraphAsync: Process error

good news for me is that "Metal Tone" and "True Heavy-3" work fine, without xruns and sound isn't glitching.

Please complete the following checklist:

1. Is this the first time you're using jack? [yes | no]
2. Do you configure jack via qjackctl or jackdrc? [qjackctl | jackdrc]
3. Is this the first time you're using rakarrack? [yes | no]

@Ray

1. Is this the first time you're using jack? [yes | no]
no, I have reinstalled several times, tried jack and jack2... if you ask about my experience with jack generally - I've been using jack for quite some time previously on Debian.

2. Do you configure jack via qjackctl or jackdrc? [qjackctl | jackdrc]
no, I haven't. Previously even tried removing those config files from home dir.. but the same.

3. Is this the first time you're using rakarrack? [yes | no]
again, term "first time" is confusing to me... if you mean first time on this installation, no I had tried reinstalling it several times, and again I haven't touched config files anyhow.

but I have to admit one thing preset "True Heavy-3" had no distortion sound previously, only clean guitar, but today I installed rakarrack once again and it works fine now without problems. the problem is I didn't have chance to track the reason it started working ok. Although, problems on "Rodent Airlines" and "Edgy" persist. So problem is partially solved. Haven't tried other presets yet.

My questions were general and distribution-agnostic, mainly to understand whether you were familiar with jack and its configuration, and in turn, determine whether this is a regression that you're facing. This is why:

* If you have been using this setup (jack + the jack configuration that you have + rakarrack) from before, then it is indeed a regression.

* If you have NOT been using this setup from before, and it is your first time running rakarrack and/or jack, then it MAY NOT be a regression.

In either case, the support we can provide is limited. You have to bring this up with the rakarrack developers (and jack if needed). Sometimes, it can be a regression together with hardware and/or system package incompatibilites introduced with updates. Something like this happened before with fluidsynth ( FS#21031 ) and none of us - including the fluidsynth and jack devs - could determine the cause.

I see