Re: [LAU] (Ardour) How to get rid of delay when recording ?

From: Harry van Haaren <harryhaaren@email-addr-hidden>
Date: Sun Feb 14 2016 - 00:11:40 EET

On Sat, Feb 13, 2016 at 9:50 PM, jonetsu@email-addr-hidden <jonetsu@email-addr-hidden>
wrote:
> JACK server starting in realtime mode with priority 10

50 is the default for processes, higher is more priority.
This machine runs jack with RT priority 89. Find out
what your top real-time priority (aka rtprio) tasks are:

$ ps -eo rtprio,comm --sort -rtprio | head -n 30

Each CPU will have one "migration" and one "watchdog" at 99,
after that you should have:
1) Soundcard interupt *
2) jackd process

* Depends on soundcard, check output of
$ cat /proc/interrupts and find the interrupt for the Delta1010

Eg:
90 soundcard interrupt
89 jackd

The important thing is the *order* of the tasks, *not* the number itself.
They are serviced based on order, as fast as possible.

> Failed to connect to session bus for device reservation Did not
> receive a reply. Possible causes include: the remote application did
> not send a reply, the message bus security policy blocked the reply,
> the reply timeout expired, or the network connection
>
> Audio device hw:M1010LT,0 cannot be acquired...
>
> Cannot initialize driver
> JackServer::Open failed with -1
> Failed to open server

Jack2 / dbus / pulseaudio issue by the looks. I'll leave this to google, or
somebody more familiar with the issue - I have JACK1 and no manual
setup of everything, so don't experience this issue ever.

> So I then used qjackctl, changed the value which was 1024, to 128, and
> *rebooted*. Now it runs with:

*Always* run jackd as the user that you will be doing the sound processing
as - do not run jackd as a system daemon while logged in as a user, it
causes headaches.

> /usr/bin/jackd -T -ndefault -dalsa -dhw:M1010LT -r44100 -p128 -n2
>
> This is quite different from the original one. Moreover, it does no
> good at all. There's crackling all over. Renoise cannot scroll the
> sequences properly, it is no good at all.

These are called xruns, that can be solved by properly tuning you
system.

> 1) Where the hell does the first incantation of jackd comes from ? And
> where do the parameters comes from ?

Your distro, or system setup. I personally advise keeping things simple,
and manually start jack when you want it started, with the exact settings
you want to start it with.

Yes this requres some JACK knowledge, but it is reliable, and consistent.

> 2) How come it cannot be started from the command line by pasting the
> command line that is currently *running* as shown in 'ps aux'

Probablty because pulseaudio takes over the soundcard when JACK releases
it. Again, keeping things simple and manually starting / stopping ensures
this
situation never occurs.

> 3) Why are the new parameters so different, lacking many original
> options ?

Dunno, I start jack with a minimal command, and it works every time :)

Hope that helps, -Harry

PS: These are known issues, and I've written up some tuning tips that I've
used in the past to squeeze every drop of RT performance from a machine:
http://openavproductions.com/real-time-latency-tuning/

--
http://www.openavproductions.com

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Received on Sun Feb 14 00:15:02 2016

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