[PD] Mess with Pd installation on Linux

Tue Dec 31 11:17:57 CET 2013

On Dec 31, 2013, at 10:12 AM, Alexandros Drymonitis <adrcki at gmail.com> wrote:

> On Mon, Dec 30, 2013 at 11:24 PM, Dan Wilcox <danomatika at gmail.com> wrote:
> Did you see this in the PD FAQ?: http://puredata.info/docs/faq/how-can-i-run-pd-with-realtime-priority-in-gnu-linux
> This confuses me a bit as it slightly differs from this http://jackaudio.org/linux_rt_config

Yeah, but both pages are doing the exactly same thing ...

> In the Pd FAQ it says that if /etc/security/limits.d/audio.conf exists you don't need to do anything, where in the other link it says that you need to create /etc/security/limits.d/99-realtime.conf and there you should write the following:
> 
> @realtime  -  rtprio   99
> @realtime  -  memlock  unlimited
> 
> In the Pd FAQ, it says that if /etc/security/limits.d/audio.conf doesn't exist, you should add the two lines above to /etc/security/limits.conf but instead of @realtime you should write @audio
> Anyway, I've followd the jack link and supposedly I've added realtime scheduling. Should I run Pd with '-rt' ?

This is just a style difference. The system will read from whichever files are in that folder. Putting the realtime lines into limits.conf or 99-realtime.conf makes no difference. 99.realtime.conf is a good idea in that it won't be replaced if the main limits.conf if altered on a system update. Also, the groupname you use is arbitrary, "audio" or "realtime" will work either way (but don't mix them).

There is lots of info out there but I think, perhaps, you're confusing yourself and/or somehow missing, conceptually, the point of all of this. I don't write that in a bad way as I went through the same thing when I switched to Linux. It's easy to start following articles and forums at first the tweak this and that ... but in the long run you just have to learn the *why* of what you're doing and not just the *how*.

Let's look at Pd + Jack. From my experience with Linux, (some of this may have been updated by now, but I don't think so), there are 2 low level audio APIS: OSS & ALSA. OSS was the original, but ALSA has the predominant interface for apps to connect to audio hardware. From a user point of view, it's main problem is that it does not do mixing of audio streams aka you can't open multiple audio programs and have them play sound together using only ALSA. You need something else to help out, enter ESD (Enlightenment Sound Daemon), Jack, & Pulseaudio which are simply software daemons running on the background that take audio streams from apps and mix them before sending the result to ALSA.

ESD & Pulseaudio are focused on the day-to-day desktop environment while Jack is mainly for professional audio work aka *fast, low latency audio*. This is an important difference. ESD & Pusleaudio are mainly just providing audio for your youtube video or music player, so you won't mind or notice that they buffer and run at a pretty long latency (say 1024 samples per buffer +, etc). A long latency means the cpu doesn't have to process that stream as quickly and the sound server (ESD/Pulse) doesn't need to run at a very high priority. Jack, on the other hand, is designed for *realtime* performance aka getting everything to process as fast as possible so you have the lowest latency possible, say a length of 128 or 64 samples per buffer. In order to allow Jackd to run as fast as possible, we have to tell the system that it should have the permissions to receive more resources and run faster than other apps, hence needing to unlock the realtime limits.

Ok, if we can now run Jackd in realtime mode, we should try and run our audio apps as fast as possible as well, if they support it. Why? Because, they may not be able to deliver the samples as quickly as Jack wants, resulting in audio dropouts (clicks). For Pd, there is the -rt start flags which starts Pd with realtime priority. Again, needing this really depends on your system, but it's a good idea to run Jack & Pd with -rt, in my experience. Years ago, I happily ran realtime audio with Jack and multitrackrecording from Pd to Ardour on a *single core* Pentium M with around 1.6 GHZ which was a beast compared to the early 2000s, but is a mouse by today's standards.

> I guess I'll have to read the manual.

Aha. Well, welcome to Linux ... :D In the future, though, it would be helpful if you did that before trying to get the pd-list to help you step by step through the process. They coudl be doing other things, like improving pd :D On the other hand, perhaps there is not the *right* info out there now and perhaps we need to have a How To Jack + Pd added to the Pd FAQ?

Also, I *really* hope you're using a GUI for Jackd like QJackCtl: https://en.wikipedia.org/wiki/Qjackctl 

> On Dec 30, 2013, at 3:31 PM, pd-list-request at iem.at wrote:
> 
>> From: Alexandros Drymonitis <adrcki at gmail.com>
>> Subject: Re: [PD] Mess with Pd installation on Linux
>> Date: December 30, 2013 at 3:30:47 PM GMT+1
>> To: yvan volochine <yvan.pd at gmail.com>
>> Cc: pd-list <pd-list at iem.at>
>> 
>> On Mon, Dec 30, 2013 at 4:12 PM, yvan volochine <yvan.pd at gmail.com> wrote:
>> 
>> On 30/12/13 14:29, Alexandros Drymonitis wrote:
>> I've realized that I need to open pd with sudo in order to have it work
>> with jack (I also have to open jack with sudo in order to use the
>> firewire).
>> 
>> as IOhannes said, you _should not_ do that..
>> (if you do it could mean that you did not add yourself to the `audio` group, as suggested by my previous link)
>> Ok, I was opening jack with sudo before you posted the link, now I can indeed open it without sudo and it will see the firewire, no prob. So I'm also opening pd without sudo, but I get the same behaviour. Sometimes it works, sometimes it doesn't. 
>> 
>> how do you start jack? can you post here the full command?
>> jack -d firewire (I use & if I want to open pd from the same terminal window, but don't really know how to turn off jack afterwards..)
>> 
>> 
>> y
>> 
>> -- 
>> http://yvanvolochine.com
>> http://soundcloud.com/yvanvolochine
>> http://soundcloud.com/elgusanorojo
>> http://github.com/gusano
>> http://vimeo.com/yv
>> 
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> 
> --------
> Dan Wilcox
> @danomatika
> danomatika.com
> robotcowboy.com
> 
> 
> 
> 
> 
> 

--------
Dan Wilcox
@danomatika
danomatika.com
robotcowboy.com

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