I put Matty in the Aquariam Bouncer and that has gentle soothing noises. I don't think that was too stimulating for him, he'd often drift off to sleep in it. We had one from 4 weeks, he still loves being in it now and he is 15 weeks. He'd also spend some time in the Hug A Bub on me.

I'd agree with putting them in a bouncer and letting them watch you. Some of the others also have a kick and whirl carnival which you can out them down on the ground with and they make music and the like.