[LAD] MIDI jitter - was: automation on Linux (modular approach)

[Ralf Mardorf]

David Olofson wrote:
> On Thursday 25 March 2010, at 14.55.41, Ralf Mardorf <ralf.mardorf at alice-
> dsl.net> wrote:
> [...]
>   
>> Mobo: M2A-VM HDMI
>> Graphics: ATI Radeon X1250-based graphics, *onboard*
>> Slot for another graphics is an PCI Express slot, no AGP etc.
>>     
> [...]
>
> Have you disabled all BIOS and other power management, CPU clock throttling 
> etc?
>   

My audio sessions start like this:

    #!/bin/sh
    # sh start-session

    [snip]

     ### CPU ferquency scaling
     echo "\nSetting up CPU frequency scaling for 64 Studio 3.0-beta3"
     cpufreq-selector -g performance
     if [ $? = 0 ] ; then echo "Done" ; fi

    [snip]

I'm not sure if I have disabled any power management by the BIOS, but I 
guess I did.

> Are you using fbdev (VESA graphics) or similar, or are you using the 
> "hardware" text mode console?

Might be a hint?! I've no time to search the web now, I'll do it tonight 
or tomorrow. I don't know what "fbdev" and ""hardware" text mode 
consoleI" does mean. I tested the VESA driver and the non-propritary ATI 
driver. There was no audible difference.

> The latter can cause trouble with some 
> integrated graphics solutions, that don't actually *have* text modes, but 
> emulate then through BIOS super-NMIs. This can block any normal IRQs for tens 
> or even hundreds of milliseconds! I doubt a desktop oriented motherboard with 
> ATI or nVidia graphics would have this problem, but you never know.
>
>
>   
>> I suspect the graphics and the USB device causing to much MIDI jitter.
>>     
> [...]
>
> Have you tested it with another "known working" computer? Could be an issue 
> with the driver or the hardware...
>   

I didn't test the swissonic USB MIDI interface with another mobo that's 
"known working". A big problem is, that the people I know don't use 
Linux, or they do use Linux and do have issues too using external 
hardware, but having the advantage that they don't need external synth, 
but just soft synth.

> Also, are there any other USB devices connected to the same hub?

The MIDI interface is the only device using USB, resp. sometimes, when 
not making music, I'm using an USB stick.
Rui told me to make the used USB slot head of the USB slots by editing 
rtirq. This didn't change anything.

> (Integrated 
> or external.) Are other devices sharing IRQ with the USB hub the MIDI 
> interface is connected to?
>   

IIRC no, but perhaps I don't remember correctly or I didn't check it 
correctly.

I won't add a complete hwinfo or anything else now. Perhaps you are able 
to tell me how I should check used IRQs.

Thank you for your "support",
Ralf