Evangeline- I think you may be referring to the touring production of Sweeney Todd that is out now. In it, there is no orchestra, but the whole cast is on stage the whole time and they all play instruments. When they’re not acting a scene they are accompanying whatever is going on musically. it’s a fantastic show and I highly recommend you see it if you get the chance. The ‘orchestration’ is very stripped down and at times almost non-existent, but it works very well and actually makes it easier to hear and understand the singers. The most incredible thing is that for the entire show, which is almost 3 hours long, the whole cast plays their parts from memory!