AMsynth as LV2 in Qtraktor dies when cpu scaling kicks in

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What steps will reproduce the problem?
1. create a qtraktor session and load AMsynth LV2 plugin in a channel
2. connect midi keyboard an play some notes > OK
3. now wait (10sec) untill cpu scaling kicks in

What is the expected output? What do you see instead?
expect that amsynths plays normal
instead i get error messages in qtraktor message window (see att file) + 
amsynth sounds all messed up (crackled)

What version of the product are you using? On what operating system?
amsynth : see file in att,  running ubuntu studio 14.4 64bit

Please provide any additional information below.
disabling cpu scaling fixes the problem
other LV2 synth plugins in qtraktor dont have this problem

Original issue reported on code.google.com by thijsvan...@gmail.com on 30 Mar 2015 at 9:02

Attachments:

• AMsynth_Qtraktor

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Is there any particular preset that triggers this problem, or is it widespread?

Original comment by nickdowell on 31 Mar 2015 at 7:18

• Added labels: Performance

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i tried this on the standard qtractor version that came with ubuntu studio 
(0.5.11) and then i also built qtractor from source a couple days ago (ver 
0.6.5.25) and the result is the same

the amsynth settings are irrelevant 

i check the cpu scaling like this :
tvanseve@tvanseve-ThinkPad-W530:~$ cat 
/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
ondemand
ondemand
ondemand
ondemand
ondemand
ondemand
ondemand
ondemand

and set it to performance like this :
echo -n performance | sudo tee 
/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor > /dev/null

the cpu scaling is probably not the root cause, but i think it triggers 
something that makes amsynth do weird stuff
i started suspecting cpu scaling when i saw that amsynth was playing ok as long 
as i kept playing my keyboard
then if i left it alone for a couple of seconds (10sec aprox) i saw the error 
messages in qtraktor and when i started playing again i heard the crackles for 
a split second.
after that the sound is ok again untill you leave the system alone for 10sec .. 
etc

using this : watch grep \"cpu Mhz\" /proc/cpuinfo
you can see realtime cpu freq info, and when scaling is set to performance all 
cpus run at 1600Mhz all the time
when set to ondemand the cpus drop to 933, and after 10 sec the freq of all 
cpus starts to jump up and down.  thats when the problems occurs

setting cpu scaling to powersave (all cpus fixed at lowest freq) the system 
simply doesnt have enough power and the sound is always crackled

i hope this is of some use to you

grtz
Thijs

Original comment by thijsvan...@gmail.com on 1 Apr 2015 at 8:40

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typo : watch grep \"cpu Mhz\" /proc/cpuinfo
should be : watch grep \"cpu MHz\" /proc/cpuinfo      (captial H iso h)

Original comment by thijsvan...@gmail.com on 1 Apr 2015 at 9:19

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fyi: i am playing with automation of AMsynth parameters (trough qtraktor) and 
for some reason the AMsynth gui seems to lag behind
when i turn a knob on mi midi controller the knob on the gui lags behind and 
the movement is jerky
the calf monosynth plugin gui shows no delay and the knobs turn very smoothly
this has nothing to do with the cpu scaling, but it might be related since it 
also seems to point in the direction of load (?)
i'll do some more test asap

Original comment by thijsvan...@gmail.com on 9 Apr 2015 at 10:49