| I'm not sure if this is what you are looking for. If you are looking for a practice tool so you can play your bass silently while others in you home or building don't have to hear you, the Pandora's Box by Korg will do the trick. I have one. It lets me practice while my wife and kids sleep. It also has a built in tuner, drum machine, phase trainer and other effects and amp modelers. I plug my CD player or iPod into it and practice tunes for the band. It can even detune the song to the key your band is playing it without slowing or quickening the tempo of the song. It can clamp to your guitar strap. It is about as big as a typical Boss pedal, but lighter and without as much depth. I love the thing, and it's now cheaper than when I got it when it first came out.
There is another device made by a different company that has a built in CD player in it, although I'm not too familiar with it.
Hope I helped. | 
