Sound synthesis problem

I spent the last month packing and moving, but I'm now back online (at last!).

Why doesn't this code work?



Here's what works:

1. Click either "Play" button; a note will sound, and the button's name will change to "Stop".
2. Click the same button again to silence the note; the button's name will change back to "Play."
3. Click the other "Play" button; a different note will sound (an octave higher than the first note); click it again to silence it.

So far, so good.  :-)

Here's what doesn't work:

1. Click on either "Play" button, sounding a first note.
2. Click on the other "Play" button, sounding a second note while the first button is still sounding.

Bad things now happen.  The sounds do not blend (as one would expect octaves to do), but instead grate against each other in a nasty alternating, overlapping grind.  Also, the application's performance slows to a crawl. Click on either button, to silence its note, and you'll see that it takes forever for the button to respond to the click.

I'm not sure how to fix this.  The code seems to be working as intended. The flaw seems to be in how I'm using Flex/Flash's sound architecture -- that is, my tactics are correct, but my strategy's wrong.

Comments welcome.  :-)