[LAU] Fwd: Re: Raspberry Pi and real-time, low-latency audio

[Jeremy Jongepier]

[...]

>>
>> A few steps ahead more.
>>
>> I red again the wiki and got to start Jack with the onboard soundcard
>> just as it says: jackd -d dummy.
>>

Hello Carlos,

JACK should now work with the onboard audio if you're using the latest 
kernel and firmware updates.

>> Then I tried to start jack with the UA25EX. I pluged the usb/power
>> cable to a laptop this time, instead of using the mobile usb charger
>> as before, and RPi doesn't reboot. Great.

You really need an adapter that does at least 2A. Using your laptop to 
power a RPi and an USB audio interface most likely won't work.

>> Now I tried to start jack on RPi through Qjackctl on the laptop with
>> ssh -X. Jack crashed every time. I tried on RPi itself and same thing.
>> Then I checked jack log, ps -A and realized that pulseaudio was
>> running and jack couldn't have access to the device. I made a quick
>> search and then I made two things:
>>
>> 1) created a config file to prevent pulseaudio to restart every time
>> It is killed: ~/.pulse/client.conf with "autospawn=no" inside.
>>
>> 2) kill pulseaudio with "pulseaudio -k" when I run jack, and
>> configured same thing on Qjackctl preferences to execute it before
>> starting jack.
>>

Afaik PulseAudio is not installed by default on the Raspbian image so 
I've never encountered this issue myself.

>> So now I have an RPi that can start jack using UA.
>> But now there is the next problem: jack starts ok but when I try to
>> connect any program (sooperlooper i.e.) or just system-in to
>> system-out ports the driver crashes (that what messages say), lights
>> on UA switch off and, oddly enough, jack still running.
>>
>> That's it for the moment.
>>

I've had the same issue. As you describe later you have to switch the 
USB controller to USB 1.1 mode and disable Advanced mode on the UA-25.

[...]

> One step more, this time with success.
> Given the situation mentioned before I tried to step back a little.
>
> First, I tried only to run jack using jackstart script again. A few
> tweaks and could make jack to work, but sound had glitches and
> crackles whatever config I tried.
>
> Second, I stepped back a little more.
> I executed again Ampbrownie setup.sh with option 2 (update and install
> additional packages). During this it changed jackd2 to jack1
> uninstalling it. This could be installed before as a dependence of
> some of the apps I installed in addition to those that setup.sh script
> install (maybe sooperlooper or rakarrack, not sure).
> Then, I noticed during rebooting that USB is only 1.1, so I changed
> the hardware switch on the back of the UA from advanced driver to
> normal.
>
> One more reboot and... Voila! Sounds was almost perfect and delay
> acceptable, practically RT, connecting in to out and using Rakarrack
> with some basic effects.
>

The AmpBrownie script definitely needs some more refining. I've forked 
it in my GitHub (https://github.com/AutoStatic/ampbrownie) to make the 
necessary adjustments so Adam of AmpBrownie can merge them back again.

> Don't know if this success is due to some newer versions it appears to
> have been updated on repos that are newer than those installed on
> first run of setup.sh, or maybe some of the modifications mentioned
> flicked the switch.
>

It's because of the controller switched to USB1.1 mode and your UA-25 
running in non-advanced mode. And Jack1 also plays a role, from my 
experience it runs better than Jack2 on the RPi.

> I made a backup with dd, of course, and I'm moving towards setting up
> RPi as a Jam/Improv/Live headless station: boot an then run Rackarrack
> as a multifx connected to Sooperlooper/Freewheeling as a looper, using
> an external audio card and a MIDI-USB pedalboard. And then improving
> step by step until reaching the limit on RPi processing and
> overclocking.
>

Maybe this could be helpful:
https://github.com/AutoStatic/scripts/tree/rpi/rpi
https://github.com/AutoStatic/configs/tree/rpi/rpi

> In the future I have more plans in mind, but for now that's it.
>
> BTW, I managed to connect a second usb device without RPi rebooting
> because of problems with power with two USB power adapters.
> So now I have:
> - 1 USB power adapter to the RPi,
> - 1 USB stick for the system partition on USB port1,

So you're running from an USB stick? I've tried this when testing a RT 
kernel but performance was horrible. But maybe this was because of the 
RT kernel.

> - 1 4 USB hub on USB port 2 (where external audio card and MIDI-USB
> pedalboard is connected)
> - 1 USB power adapter to the second mini-USB port on the MIDI-USB
> pedalboard that helps to feed it and to stable the overall setup.
>
> I think both USB power adapters are mobile adapters, I think 0,7A and
> 0,5A, so maybe with just one USB power adapter at 2A for the RPi I
> could connect all this and a qwerty keyboard and something else, which
> now I can't. That or just a powered USB hub, but that is more
> expensive.

I'm using a powered hub with a 3.7A adapter which is more than enough. I 
bought this hub for €3, wouldn't call that expensive ;)

Regards,

Jeremy
>
> Hope it helps.
> Thanks all and Regards.
>