[PD] Use Alsa while other devices are using alsa?

[Peter P.]

Hi list,

on my Debian system I can easily launch two instances of the mplayer
media player or audacity which will then send their audio to alsa and to
the same soundcard without blocking each other. When I try to do the
same with Pd I do get the well known 
"ALSA output error (snd_pcm_open): Device or resource busy"
Why are some programs capable of using alsa together with other programs
and Pd not?

Thank you for all explanations, I am most looking forward to
understanding this topic better.

cheers,
P