while it's usually not actually necessary to generate a stereo signal
(alsa's default plughw device will happily duplicate it for us), we
still do it for demo purposes, just because.
a more realistic demo would actually use numpy, as that's what the
library will most likely be used with, but anyway.
the thread in the background actually needs time to do something
sensible. this is most easily achieved by simply sleeping in the
foreground thread.
i addition to the 440 Hz tone, also play 1 kHz, to demonstrate how
the change() function is used.
there is no need to be pedantic about the period size, especially with
a blocking device. what's more, attempting to set it on an already
playing device would error out, and it would be rather counter-
productive to temporarily stop it.
Added isine as an example for interactive generation of sound.
git-svn-id: svn://svn.code.sf.net/p/pyalsaaudio/code/trunk@33 ec2f30ec-7544-0410-870e-f70ca00c83f0
