So pd works great so far, except that it wants to hog all audio output on my system. If any other application is using audio (alsa), then i see "snd_pcm_open (output): Device or resource busy" from pd on the command line when trying to select the alsa output device in the gui. Any other apps gladly mix together (e.g. I can run as many mplayers or whatever as I want and they all have sound): it appears the alsa dmix plugin is enabled by default in the latest versions of alsa, and furthermore I think my card has an analog mixer too, but I'm not actually sure which method is being used by any or all of my other applications (dmix or the hw mixer). Still, pd is the only one that doesnt want to play nice. If all other sound using applications are closed, pd works fine.

I have preemptively posted some info if it might help in a diagnosis:

$ cat /dev/sndstat 
Sound Driver:3.8.1a-980706 (ALSA v1.0.14 emulation code)
Kernel: Linux pompeii 2.6.22-14-generic #1 SMP Tue Dec 18 08:02:57 UTC 2007 i686
Config options: 0

Installed drivers: 
Type 10: ALSA emulation

Card config: 
HDA Intel at 0xee400000 irq 21

Audio devices:
0: AD198x Analog (DUPLEX)

Synth devices: NOT ENABLED IN CONFIG

Midi devices: NOT ENABLED IN CONFIG

Timers:
31: system timer

Mixers:
0: Analog Devices AD1981

$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Intel [HDA Intel], device 0: AD198x Analog [AD198x Analog]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 0: Intel [HDA Intel], device 1: AD198x Digital [AD198x Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

It should be noted that my distro/alsa install did not create an /etc/asound.conf by default, and everything seems to work without it.

Ok this issue has been solved after talking to an alsa guru. I did an ltrace on pd and found that my two options for an alsa output device, "HDA Intel (hardware)" and "HDA Intel (plug-in)" both resulted in an attempt to open hw:0 and plughw:0 directly, which, according to my guru, bypasses dmix. He said sanely coded alsa apps will try to open the "default" device. So, to run pd now I do it with "-alsa -alsaadd default". Adding that last option gives an extra, blank entry in my list of output devices on pd, which, when selected, seems to use dmix properly and allows pd to share the audio out with other apps. I think I may send this to the pd-dev list for a possible bug report as well, if anyone thinks that's necessary.

Thanks for posting your solution and clear explanation. This is bound to come up again.
cheers,
andy

Btw.. has anyone solved the perennial "latency sucks on Windows" problem yet? We need a clear howto on this for the Wiki.
cheers,
andy