The trouble with using the SICP video lectures as audio source material is that the sound is pretty terrible. It has a lot of background hiss, and because they've used automatic gain control while recording, the amplitude of the hiss changes during the transitions between speech and silence.
Having said that, carefully using the Noise Reduction and Dynamics Processing commands in Adobe Audition can increase the quality very well for this sort of thing. I'm not finished with it yet, but I'll post a clean copy of Lecture 1a's audio track when I'm done.