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Re: [fluid-dev] [Rosegarden-devel] Problems With Rosegarden Using Qsynth

From: Aere Greenway
Subject: Re: [fluid-dev] [Rosegarden-devel] Problems With Rosegarden Using Qsynth or Fluidsynth When Using PulseAudio Instead Of JACK
Date: Thu, 31 Jan 2013 21:13:42 -0700
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130106 Thunderbird/17.0.2

On 01/29/2013 02:59 PM, Aere Greenway wrote:
On 01/29/2013 01:55 PM, D. Michael McIntyre wrote:
I don't have a clue why Rosegarden is causing this and MusE isn't.  Upon
a superficial and quick comparison, they both appear to work the same
way in the case where QSynth is already running, and it's configured to
use pulseaudio: they both start with audio support disabled, due to
being unable to start jackd, because pulseaudio has control of the hardware.
Michael, and all:

Perhaps that is a significant clue to the problem.

JACK seems to have made great strides lately. Where it used to not co-exist with anything, it now seems to get along with most everything.

You can now play Internet videos with sound while JACK (QjackCtl) is running, and can run all sorts of things together with it. On the other hand, Audacity doesn't get-along with it at all.

If you look in the QjackCtl "Connections" dialog, in the "Audio" tab, you now see a "PulseAudio JACK Sink" and a "PulseAudio JACK Source" device. And the ubiquitous hangs seem much harder to cause.

I had concluded, based on my testing on several desktop computers in my test-bed, that they had finally solved all of the problems, and that JACK nicely gets along with everything. They seem to have even put those fixes in the Long-Term-Support release, 12.04, because it behaves just as well.

But then I tried the same test on my Acer Aspire laptop, and my new MIDI device initially trying to use the (PulseAudio) Java Sound synthesizer (with QjackCtl already running), hung it tighter than a drum, and I had to power the machine down.

So I guess all is not yet well on the JACK audio front.

The significant clue in what you said, was that Rosegarden would fail to start jackd, and would thus start up without audio support.

In doing the test, there was no warning about audio support being disabled (that I in the past always used to see in such situations). Where they now co-exist better, it probably succeeded in starting jackd. But perhaps, they don't successfully co-exist in other ways.

As you pointed out, running with JACK is much more efficient. Where processor usage was around 75% using PulseAudio, the same piece played using JACK had a processor utilization of around 25%, which is no insignificant difference. To even get it to work without cutting-out on PulseAudio, I had to disable both the Reverb and the Chorus. I can use them when I use JACK in place of PulseAudio.

By the way, most of my testing was done on an Intel Celeron CPU 2.53 GHz desktop machine, running Lubuntu 12.10.


The information in the next-to-last paragraph above (about the processor utilization using PulseAudio and JACK) was incorrect.

The numbers I remembered were correct, but the numbers were not from the same piece.

When I revisited this test, using the same piece, the processor utilization was 75% (for PulseAudio), and 55% (for JACK). The difference is still significant, but not as great as I formerly reported.


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