Since it was introduced, the SoundCloud Record button has been hard to get to work in Ubuntu and other GNU/Linux distributions. Fortunately, my buddy Omid, who is a SoundCloud developer, has found a solution.
It turns out the problem is caused by a “Linux-specific security feature” (read: bug [login required]) that prevents a Flash settings dialogue from appearing when wmode=opaque is used. In any case, there are a few easy workarounds.
If you’ve got the flash-player-properties package installed (which, at least on Ubuntu, ships separately from the flash-plugin, but is available in the standard repositories), you can add “a1.sndcdn.com” to the allowed sites under the “Camera & Mic” tab of that program.
Otherwise, if you’ve unsuccessfully attempted to record at least once on the SoundCloud upload page, you can add a1.sndcdn.com from the Flash player’s web settings panel. While you’re there, check your security settings!
Hope this is helpful to other SoundCloud users on Linux who haven’t quite been able to get recording working.