Comment 7 for bug 227067

ok - i had a chance to do a little investigation. Seems that its the stock jackd thats the problem... its just not up to the job.

Here's what I did.

1) installed rt- kernel
2) my soundcard runs as INT-22, so I did chrt -p 99 `pidof "INT-22"`
3) enabled memlock and rtprio in /etc/security/limits.conf
   @audio soft rtprio 99
   @audio hard rtprio 99
   @audio - memlock 512000
   @audio - nice -19
4) used qjackctl to enable realtime and scheduling priority of 80, as recommended

ok - jack now realtimed, as is the soundcard.

now to get a test program...

i installed libjack-dev and libasound-dev

i then got the source distribution for mpg123 v1.4.2 (from sourceforge)

./configure --prefix=/home/richja/mpg123
(configured oss, alsa, jack)
make
make install

now i have mpg123 ( a very performant and lightweight mp3 player) configured for alsa and jack

so NOT running jack

% mpg123 xxx.mp3
 - picks alsa driver - perfect sound - virtually 0 CPU.

running jack as above

% mpg123 xxx.mp3
 - picks jack driver - instantly audible audio drops, jack messages of: "alsa_pcm: xrun of at least 0.007 msecs", delay of 21329.000 usecs exceeds estimated spare time of 10626.000; restart, also clear audio artifacts. totally unusable.

hope this gives more info.