Installing and using JACK audio - my adventures in Mint17

[Flemur]

I was wanting to setup a guitar "effects rack" sorta thing using LADSPA effects. "Normal" audio has too much latency, and supposedly "jack" (jackd) will allow real-time effects. So I setup a separate Mint17 install to play with it.

The jack documention I've seen, or watched on youtube, is really bad, so here are some notes I took while installing and getting sound output from ardour3, vlc, and audacity.

+++++++++

Remove pulseaudio, install jack and some utils. Reboot.

qjackctl -> Start
"Cannot lock down 82274202 byte memory area " ...etc.
IOW, Jack server won't start.

1 - add "username" to "audio" group

2 - /etc/security/limits.conf: Add 2 lines at end:
@audio - rtprio 99
@audio - memlock unlimited

Reboot

Jack Server now starts OK.

+++++++++++++++
START VLC -
Error messages about can't open sound output.

qjackctl -> Connect -> All connections are "capture_N" (1,2) or "playback_N" (1-8)
What the 8 playback things are I have no idea!
No mention of vlc.

VLC UNRESOLVED.

install vlc-jack plugin; now vlc doesn't complain about sound, but still no sound.

w/vlc, select jack audio output thru Tools->Prefs->Audio
HAVE THE JACK SERVER RUNNING.

+++++++++++++++++++
START ardour3

qjackctl -> Connect -> shows plenty or connections, named audour, automatically connected.

ardour3 unresolved.
(same for audacity - shows audacity connections, no sound).

+++++++++++++

qjackctl: changed Setup->Interface to hw:0 (from 'default')
Start jackd, got this error:
ERROR: cannot register object path "/org/freedesktop/ReserveDevice1/Audio0": ...

Fixed that with
$ killall -9 jackdbus
...then jackd server starts (IOW, it was two stupid to know it was already using hw:0).

Still no sound output.
+++++++++++

qjackctl -> Setup -> Interface = plughw:0 (No tutorial mentions this!)
PRESS "PLAY" button (no tutorial mentions this!)
SOUND! From audacity! AND VLC! And Ardour3!

+++++++++++++++

At this point I can't record anything using jack, so I'll post updates if/when that happens.

With audacity I can record line-in by shutting off jack server and selecting alsa in audacity, tho the pass--thru sound is distorted, sometimes the recorded wave file is distorted and sometimes audacity crashes.

Adobe audition(+wine) records fine.

[Flemur]

Update: I can now use linux as a guitar effects rack with no noticeable delay/latency! And it only took about 10 hours!
Using "guitarix" effects box. Showing about 2-3% CPU use with effects running, which is pretty good.
Note: I didn't have to make or change any connections in qjackctl tp use guitarix.
Will give rakarrack a try next.

Anyway, here are some more notes that may help someone else trying to use linux audio & jack - good luck!

DISCOVERY: I was using audio input from a TV cable box, and thru the computer it was out of sync with the TV sound, by about 200ms (1/5 second). Turns out the delay was IN THE TV! (TV audio later than audio from the cable-box it's connected to). I've never heard of a TV buffering sound and picture, but this is a "smart" TV, so I guess it out-smarted me. Taking audio from the back of the TV kept TV and computer sound in sync.

Not much luck with ardour3!

Ardour3: recorded some sound from TV - no delay; no effects (can't find them in Ardour menu...sigh)
Saved the recording as a "CD" (.wav?) file:
["ardour3" The selected preset did not load successfully! Perhaps it references a format that has been removed?]
Got a wav file (21Meg), silent. Same as above with .ogg.

Found some stuff about ardour3 export: "Turning off the ALSA-Audio bridge for the export process did the trick."
That's truly lame.

So I couldn't find any mention of ALSA-Audio bridge (and no "alsa" in "ps -ef") in ardour or gjackctl, so stopped the jack server and tried the export again...ardour3 instantly crashed:
JACK HALTED: JACK server has been closed

(ardour-3.5.308~dfsg-1:6386): glibmm-ERROR **:
unhandled exception (type std::exception) in signal handler:
what: basic_string::_S_construct null not valid
[1]+ Trace/breakpoint trap ardour3

Great stuff! Linux audio is the only thing that makes me miss windows...

[autumnleaves]

I am also in a wrestling match with Mint 17 audio. My sympathies!

[Flemur]

autumnleaves : I am also in a wrestling match with Mint 17 audio. My sympathies!

My sympathies back atcha! It's like pulling teeth. Your own teeth.

I put the process on hold (IOW, gave up) until I discovered that TV sound delay issue; the delay was short enough that it was hard to tell which was first unless you stand between them and listen carefully. Lesson learned: don't assume anything.

A bright spot is the "hydrogen" drum machine: works great, very flexible, GUI makes sense, works without "jack", and DOESN'T CRASH.

Edit:
To record the guitar+effects with audacity:
"Audio host" = jack
"Input device" = guitarix_effects" (or something like that), not jack.
(those settings aren't labeled - that's what the mouse-over pop-up help says)
When I selected "guitarix_effects" input the first time I got error messages, then later it worked.
IIRC, guitarix_effects=stereo and guitarix_amp=mono.

Also: Rakarrack's help consisted of a good explanation of audio inputs & impedance matching when using electric guitar as input.