Schluter DITRA is a thin waterproofing membrane that also decouples the tile from the substrate so it is less likely to crack. It is definitely not sound proofing or sound insulation and would offer little reduction of structure and air borne sound but the tile will help. It is orange so I assume that is what is being installied.

Schluter also makes DITRA-SOUND which is a heavy polyethylene mat with a fleece surface on each side. It should reduce structure borne sound transmission like foot traffic but will do little to reduce the transfer of air borne sound however the tile will help with that.

Modern codes require a minimum level of sound separation between apartments and that should be designed into the ceiling below. To reduce footfall sound transfer from hard flooring a resilient underlayment is needed. Its difficult to determine how much more resilient DITRA-SOUND would be but it is not much thicker than DITRA so it would be the better choice. But that would be moot if you have already installed DITRA.

I'd see if your condo association has any rules/regulations/guidelines in place.

I do some work in Manhattan and most places I've worked have very specific guidelines. Most simply specify a minimum IIC rating, usually between 50-60. Some actually specify materials. 50 is usually the minimum for basic residential, most condos/apartments are in the 55-60 range.

The Schluter link you provided says that a Ditra floor has an IIC of 38. When I need a sound control membrane, I usually look at Nobel SIS. I don't recall the exact IIC, but I'm thinking 62. Ditra won't get me anywhere for sound control. Nobel SIS will.

Way back when I was looking, I never found an IIC for Ditra-SOUND, even after emailing the company. Back then they listed a generic "IIC greater than 50" which does me no good at all. I'll take a listed "62" over a "greater than 50" every day of the week.

SIS is a thin membrane and it's also a crack and waterproofing membrane. At 3/64" thick, it's a little thinner than Ditra.

For added info, there are two sound transmission acronyms:

SSC is for the transmission of airborne sound; conversation, television, or music, etc.

IIC is for impact noises. Footfall, high heels, etc, through a floor and into the room below.

No, they accomplish different tasks and not used together