I have stumbled across "Songmaven", and it looks like it could be a very useful resource for those who don't know of it already. This is a link to the home page. Among the tools are a downloadable set of MP3 blues backing tracks (which are also directly playing via an audio widget on the homepage. As I'm currently learning blues scales on the alto sax, these could be perfect for improvising around. I assume they are in concert pitch, though and I'm not sure which key goes with which backing track. For example, if I'm playing the D blues scale on the alto (Eb) which blues backing track should I play? I tried several to see which fits and to my ear, it seems as if playing the E blues backing track works when I play the D blues scale. But that doesn't seem to work out logically. An suggestions on how to work this out easily would be welcome.