Ubuntu Studio Users:
I think your plan to move Ubuntu Studio to Xubuntu is a good one. It
seems to have the lowest overhead of any of the Ubuntu versions.
But it seems there are problems with the kernel itself, which even the
lower overhead of Xubuntu cannot solve.
I have been working with the Fluidsynth developers to address another
problem, and in doing so, discovered the performance problem the testing
below attempts to quantify.
All:
Your suggestion of cutting the sample rate did not seem to have any
affect that was visible to me.
It may be that I would need to run without Jack, but I need Jack because
I use audio files.
In the past, I have run without Jack, and the performance of Qsynth was
better, but not much better. I could test this further, but it is a
moot point, since I need to be able to use audio files in my
sequences.
I performed some benchmark testing on the problems I have been
reporting.
I did all of the following on a 933 megahertz unit-processor (one CPU)
machine, which has been my minimum system in my test-bed.
I tried it on Ubuntu 11.04, and on Xubuntu 11.10.
My methodology was to reduce the Qsynth polyphony parameter to the point
where my test sequence (MIDI) file yielded no underruns. I did a binary
search for the polyphony value that worked. I did not use Reverb, or
Chorus (the check-boxes were clear) in any of the tests.
With polyphony values above 16, changes of 1 (up or down) made an
observable difference.
I also noted (while the piece was playing) the Digital Signal Processing
load (shown in the Qjackctl window as Real Time Percentage (RT %).
When I got down to the minimum Qsynth polyphony value of 16, I started
muting tracks, to where the maximum # of single-note-playing-at-a-time
tracks played with no under-runs.
UBUNTU 11.04
Polyphony parameter value without under-runs: 26
DSP Load while playing: Usually in 20% range, sometimes in
30% range, max 38.9%
XUBUNTU 11.10
Polyphony paramater value without under-runs: 3 (16, with
only 3 tracks playing!)
DSP Load while playing: In the 50% range, often getting up
into the 60% range.
*Note: It will not play a single-track piano part without
generating under-runs.
>From past experience, I observed that UBUNTU 11.10 has a poorer
performance than XUBUNTU 11.10. Also, the Unity desktop appears to have
DSP Load values 20% higher than the cripple-ware Ubuntu Classic desktop
on the same machine.
As you can see, the performance of the two systems is radically
different - an order of magnitude. It is not just a minor difference.
The performance hit seems to be associated with the new kernel - not so
much the desktop. Though Kubuntu had the poorest performance of the
three I tried.
A 2.5 gigahertz unit-processor system (using the Ubuntu Classic desktop)
will run the test piece without under-runs.
I have a 1.5 gigahertz machine which I have not yet tried, but based on
the above, it will perform poorly, or perhaps marginally.
On 11.04, all of these machines would perform the test piece on Qsynth
without under-runs (though on the 933 megahertz machine, the Qsynth
polyphony had to be set down to 26).
I will do further testing with my 1.5 gigahertz machine, since this is
one of the target machines I originally planned to use.
--
Sincerely,
Aere
--
Ubuntu-Studio-users mailing list
Ubuntu-Studio-users@lists.ubuntu.com
Modify settings or unsubscribe at:
https://lists.ubuntu.com/mailman/listinfo/ubuntu-studio-users
