Music playing at the bar?

In the scene where Book and his partner walk into an African- American bar to pick up the suspect name T-Bone while Rachel and Samuel wait outside in the car, there's funky song playing loud, i really enjoyed it. Does anybody know the song/artist and is it available anywhere? Or was it just filler music produced for this scene? Anyway, i really liked it.:D

I watched Witness again yesterday and it still holds up as one the most brilliant films of all time!.