Took me months to get "into" this, but once I got the hang of using it, its OK. You have to save the drum/bass samples to user memory, then transpose the bass and store again then write the different key'd saved samples to a "song", but in doing so, there is a lot of buttons to press, which , until I got the hang of it, made this spend the first 12 months under my bed.
Its pretty restricted to very basic music unless you 1/2 all the bars, which helps a little.
Seems reliable enough, but the few people I know who have this (and the bigger of the same, just use the drum side of it and forget about the bass lines. OK you can write your own bass or drumm, but you can't put your written drum & bass together to use.
I preffer to make backing track CD's on my PC with cakewalk, which does this DR670 out of a job 100 times over.