Simply put, the RPI firmware does not work with USB audio correctly yet. See this thread: http://lists.puredata.info/pipermail/pd-list/2013-07/103261.html

I keep looking for fixes, but the way USB is handled, the only way for it to work without dropouts is to have *nothing* else plugged into the usb bus and ethernet disabled ... sucks.

On Jul 26, 2013, at 5:41 PM, pd-list-request@iem.at wrote:

From: John Canning <johnnyboy7777@hotmail.co.uk>
Subject: [PD] Raspberry Pi Behringer UCA222 boot problems
Date: July 26, 2013 5:40:49 PM EDT
To: Pure Data <pd-list@iem.at>


Hi Folks,

I have been trying for quite a while to get my Raspberry Pi to work in full duplex with Pd. I have installed the OS on the PdPi site and updated it. I am using a Behringer UCA222 for audio. When I change the USB speed down to 1 (dwc_otg.speed=1) in /boot/cmdline.txt my Pi won't boot with the soundcard plugged in. If I unplug the soundcard the Pi will boot but as soon as I plug it in the Pi crashes. Has anyone got any suggestions about why this is happening? 

Thanks,
John

--------
Dan Wilcox
@danomatika