I never realised this was a 'proper' technique but I used it all the time on my cheaper kits to get a good sound; also works with sheets of paper/card (different thickness or layered sheets to achieve the desired effect). Think I might revisit this one...Lay a cut-out head on the snare better to modulate the pitch and decay in a way that tuning and muffling cannot do. It's fat, wet, gated... just lovely! Works on a high-pitched snare, or makes a depp, loose, wet snare even deeper and loser!
Definitely worth sacrificing a new head for.
Cut a circle from a head about 1/2-3/4" smaller than the diameter drum it will go on. Overlay shouild be new, so it's flat and has good integrity with the batter. Batter shouild also be fairly flat, this doesn't work quite as well on a severely dished head. Coated or clear works just as well.
If you're not familiar with this old studio trick, you will be amazed! I always keep an overlay with my most-used snares.
Works on toms, too!