I have a second floor remodel coming up for a good repeat customer.
Here's the problem.
Part of the second floor space is used for a sound studio.  This space is over parts of the kitchen and master bedroom.  Currently this space has carpeting and pad on the floor and the noise level downstairs is 'tolerable'.  Part of the remodel will be to replace this carpeting and pad with hardwood.  We cannot tear out the subfloor or the downstairs ceiling to install anything in this space.
Here's the question.
Anybody have any good ideas for a thin, sound deadening pad that can be placed under the hardwood? 
All ideas will be listened to, the good ones will be considered.
Thanks.

Wes,

Here is a web site for a product that I have seen demonstrated very effectively at trade shows: http://www.acoustiblok.com/ .  If I remember correctly, the last time I priced this product it cost $1.50 per square foot.  The way I saw it installed was loosely over stud walls.  That is, it was not pulled tight.  For a floor application this might present a problem unless furring strips were installed so the membrane could droop.  Better still, contact this company for the latest price and whether it is applicable for floors.  

This might help: http://www.soundproofing.org/infopages/channel.htm http://quietsolution.com/html/quietrock.html?gclid=CNrW07eOtJMCFRUasgodpi_JCw http://www.gp.com/build/product.aspx?pid=1071

When I type a RETURN, they appear in the text, then I hit submit and they're gone.

Keep in mind that sound travels through solid objects better than the soft ones. So if you install the hardwood and base directly to the floor, it will transmit sound better. Especially low frequencies. It would be best to install it with some sort of pad as y'all described. But the only way to effectively filter out low frequencies is to damp them with mass, so you won't really affect those much with flooring.

The only that will stop sound is mass and an air space.  We installed the acostiblock product in our sound studio in the space above with hardwood floors. It helped a bit, but we had a double joist system to keep the above room isolated from the studio below. We still heard drums coming through the floor. Tolerable but not completely soundproof (which is nearly impossible in a residential retrofit). You could put the acousticblock down on the sub floor. Throw down a sheets of 5/8 drywall and then put a tongue and groove subfloor on top of that. That would give you the the mass and some good isolation. It doesn't give you and air space, but it should work pretty well. The key also is to seal the entire place with a good acoustic caulk sealer. 

It's a big trouble...

Another thing to consider is a light weight hydraulic cement -based subfloor such as Perlite or cellular concrete. Another still is blown in cellulose insulation.
Whatever you end up using, you must consider the added did load on the floor as well as the added thickness above the adjacent floor.