Re: Raspberry Pi and real-time, low-latency audio

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Hi, thanks for sharing.
The idea is simply brilliant and it works quite smoothly following the wiki[1] (Thanks again Jeremy!), i've got a UA25EX[2] and a Terratec Aureon dual-usb[3].
Just a couple of things i noticed:

1)Using the nexus7 power adaptor everything works fine, it's a 5w 2.0A.
2)if you run jack with following command as the wiki suggested "jackd -P70 -p16 -t2000 -dalsa -dhw:UA25 -p128 -n3 -r44100 -s" make sure to add the background "&" at the end of the line, without this the sound was lousy and glitchy, at least for my UA25EX. 3)Using this usb wireless adapter[4], so in a headless fashion, i had many jack's disconnection no matter what frames/periods i choose.Any suggestion to improve it?
4)I really love the tubescreamer in guitarix, it sounds GREAT!
5)I've got my PI amp now saved in a separate sd card, now i'm able to switch my pi from a server into an amp by just replacing the sd card, how lovely it is!?

p.s. I was thinking to install Ubuntu on my nexus7 to control Guitarix (headless through ssh -X) with the touch screen!!!

[1]http://wiki.linuxaudio.org/wiki/raspberrypi
[2]http://www.rolandus.com/products/details/970
[3]http://www.amazon.co.uk/Terratec-Aureon-Dual-USB-Notebook/dp/B000WL23KC/ref=sr_1_1?ie=UTF8&qid=1366289839&sr=8-1&keywords=terratec+aureon+dual+usb
[4]http://www.edimax.co.uk/en/produce_detail.php?pd_id=328&pl1_id=1&pl2_id=44

Nicola

On 04/18/2013 01:12 PM, Carlos sanchiavedraz wrote:
2013/4/17 Jeremy Jongepier <jeremy@xxxxxxxxxxxxxx>:
On 04/17/2013 09:49 AM, Carlos sanchiavedraz wrote:
2013/4/15 Jeremy Jongepier <jeremy@xxxxxxxxxxxxxx>:
On 04/15/2013 10:39 AM, Carlos sanchiavedraz wrote:

Just a USB cable from RPi to an A/C to USB adapter, and UA25EX
connected direct to the USB on RPi.


Check the current of the adapter, if it's somewhere around 1A you might
need
a more powerful adapter as the RPi already draws 700mA IIRC.

The adapter is the same as that ones to charge mobile phones, just an
adapter from USB to a switch. I thought it would be enough to plug the
UA to the RPi and not having to plug it to an USB powered hub, because
then it may occur problems with other devices plugged in it, and this
would probably increase problems with audio latency and such.

I haven't had any problems with audio latency and using a powered hub.


Good to know. I've had some problems before testing some other touch
device with USB, but maybe it had to do with the hub was not powered.


IIRC, when configuring using raspi-config, the Modest preset for
overclocking just increases the CPU freq from 700MHz to 800MHz. I
didn't want to risk my SD because I red that issue you mention, but it
seems that anyway I've left without my SD.

What kind of SD are you using? I've used different SD cards with
different
results. I'm now using a cheap OEM class 10 SD card that does get
corrupted
quickly but performance is better than other SD cards I've used. Whenever
I
change something I make a backup now.

I'm using a SanDisk 2GB microSD on a SD adapter for the RPi slot. I
never had any problem until now.

And that while SanDisk SD's are being recommended for use with the RPi. What
core_freq are you using?
I chose the Modest preset, so it should be just 800MHz and with no
other modification on other freqs.


Do you still can use yours once it is corrupted? I plug it, you can
see the two partitions  mounted for a moment but then it unmount
itself. I made a backup copy with dd once I configured some
parameters. I've and tried several times to transfer it to the SD with
dd again but at about 840MB transfered it stops with a corruption
error; I only can modify the scripts and config on the first partition
(boot partition) when it stays mounted for some time.

First thing I do when a SD becomes corrupted is wipe all partitions and then
restore an image with dd.
I tried it, but when I try to wipe partitions with gparted or any
other it unmount itself or say that it's not possible.

If you run into corruption errors the SD might be
defective?
At least not until now, never had a problem. I wonder if the reboot
cause a physical damage on the SD, but in a reboot it shouldn't happen
a peak of voltage to cause that.


This could allow me to maybe boot a system in a USB stick, but then I
waste one USB slot, and I'm afraid that if I buy another SD card it
could be corrupted again and then it would be wasted money.

You can boot from an USB stick connected to a hub. I've tested this when
trying to run a RT kernel on the RPi. But either my USB stick or the RPi
itself has issues with the throughput because I had the idea the RPi was a
lot less responsive and audio was completely distorted.

In worst case, I could plug a USB stick on one slot and in the other
the USB hub with the UA and mouse/keyboard/midi-usb..., but I would
like to control what happen with SDs cards and when they get
unusable/broken because of some corruption.

Jeremy

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