Gobos are really useful things especially if you're working in a sub-par recording environment (ie. your living room). So what exactly is a Gobo?
Baffle - A physical object that absorbs or otherwise reduces the volume of sound which passes through it, or is reflected by it.
Gobo - see Baffle.
In other words, It absorbs or blocks sound. Those are the 2 main ways this effect can be achieved:
1. Absorbing the sound (converting it to heat via friction) - this is what foam, cloth, and other porous materials do.
2. Reflecting the sound (bouncing it back where it came from) - this is what concrete, and other non-porous materials do.
Here's a youtube video of the finished product: