Is there a way to find out which program is using a device?

I have the error "Can't open output file '/dev/dsp': Device or resource busy"

(from xmms, vlc, artsdsp, esddsp etc.. )

but i do not know what is using the device.

A little history:
To start i had no sound problems, then occasionally i would get this error
but when i logged in again there was no problem. At this time i could ALWAYS play the test sound.
From yesterday, having seemingly not done anything to the sound system, I always have this error and currently cant even play the test sound owing to this problem.

More problems arise as i dont appear to have the arts/esddsp documentation.

(Sorry if this is a common problem, I search around abit to try to solve it but nothing i found worked on my system.)

Id be grateful for any help...

Thanks
T

Some further info on my problem....

my services shutdown to reboot i see an error about i810_audio drain dac dma