Soundflower is a Mac OS X (10.2 and later) system extension that allows applications to pass audio to other applications. For instance, you could use it to capture streaming audio from a web site (such as Wolfgang’s Concert Vault) and record it using GarageBand or Audacity. It works great (last night, I captured a 1977 Pink Floyd concert in its entirety), and best of all, it’s free!

By the way, for those who don’t know, Audacity is also free, and is a really capable audio editor. There was a brief gap in the stream while it re-buffered when I recorded the concert, but using Audacity, I was able to close the gap up with no audible glitch. One thing to bear in mind is that Audacity does not have built-in MP3 creation, even though it can edit existing MP3 files. So, if you want to be able to create MP3s, you’ll also have to download the LAME MP3 encoder (also free - the link is provided in the documentation).

Of course, you should only record streams for your own personal use, such as listening later on your iPod. It’s not nice to use tools like this to rip off recording artists. If you use this to record a song or songs, and you really like them, do the right thing and buy the CD or download it from iTunes.

Once you’ve got all the software loaded, there is a trick or two to using it. If you’re trying to record a web stream, your first step is to select Soundflower (2ch) as your default system output using the sound panel in System Preferences. Then, in Audacity, you need to select Soundflower (2ch) as the input source. To monitor the recording in progress, select your usual output (Built-in Output) as the Audacity output, and select “Software Playthrough.” All of the Audacity settings are made in the program’s Preferences... panel.

One last hint. Just to be safe, and make sure that none of the various system sounds wind up as part of your recording, go into the Sound preferences panel and turn off the “Sound Effects.”