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

[Carlos sanchiavedraz]

Hello, Jeremy.


2013/5/8 Jeremy Jongepier <jeremy at autostatic.com>:
> [...]
>
>
>>>
>>> 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.
>

Ok, good to know. At the moment my SD stick is almost full (2GB) and I
cannot upgrade.

>
>>> 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.
>

Great, I came to same conclusion given what I've been experimenting:
at least 2A.

>
>>> 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.
>

Don't know which program did install it. Anyway, when I came to
another point of safe and functional configuration I'll make another
system image starting from stock Raspbian, to clean anything rarity
caused in the process.

>
>>> 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.
>

Do you mean there is something to configure on RPi? If it is so I
think something did it. I didn't touched anything on RPi related to
USB, I just disabled Advanced mode on the UA25 turning off the switch
on the back, and I guess this is what cause the switching to 1.1. Is
it so? If not it would be great to know exactly what else to control
the situation in the future.

> [...]
>
>
>> 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.
>

Great.

>
>> 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.
>

We're refining the situation, great.

>
>> 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
>

Sure it will, thanks for sharing.

>
>> 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.
>

As the mini SD 2G card was corrupted, I just use a 64MB for the boot
partition where I specify /dev/sda2 as the system partition. For the
moment it all went quite well. As I mentioned before, it runs RT
without a problem.

>
>> - 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 ;)
>

That's really cheap. I have to find something similar to avoid more
power issues.

> Regards,
>
> Jeremy
>
>>
>> Hope it helps.
>> Thanks all and Regards.
>>
>
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Thanks so much, Jeremy.

-- 
Carlos sanchiavedraz
* Musix GNU+Linux
  http://www.musix.es