[Terry C]

I've been checking into ways to bolster sound-proofing in an existing
wall, and it occurred to me that the recording gurus on r.a.p. may
have experience doing this.

Basically, it's one large, long wall that was built by artists in an
NYC loft, so it's probably standard cheap sheetrock over studs. The
current wall is acoustically transparent, even to mid and high
frequencies.

Is there any effective way to provide better soundproofing by
installing a second layer of sheetrock with better sound blocking
qualities?

Any suggested materials or construction techniques would be much
appreciated.