I have a Mac (bass) and many of the CDLCs that I download have no bass sound or tone.  If I play one of these songs, then all the others that follow (normally play ok) have no bass sound either. Any ideas?

Sounds to me like the makers of those CDLCs didn't designate a tone for the bass, and as a result, the toolkit probably defaulted the bass to a "guitar" tone (if there even was one). This will cause Rocksmith's tone mechanism to break, and it will remain that way until you restart the game.Are these CDLCs all made by the same person? If so, it might be easiest to bring this to their attention so they'll be able to fix it for you.

Thanks for the response.  I believe it stems from songs without a custom tone.  And yes I downloaded a series of songs from a creator that did not provide custom tones.

Ok, that explains it. It's not you, it's just that he made all of his songs in the way that I described above. so they're all going to be like that.