Originally Posted by RickenBoogie
There's no pedal or device that I'm aware of that will accurately transpose your pitch like that.
There are several available on the market, the most norotious being the Morpheus Droptune.
It's polyphonic, you set and it transposes whatever you play.
I still prefer to detune or use an octaver.
If you do a lot of covers with various singers, a 5 string bass really is the way to go. It makes your life much simpler.