Despite what some are claiming, there are numerous older PPC-only _audio_ specific programs that will not work satisfactorily on Intel Macs. Some of these older OSX PPC _audio_ program won't even install on Intel system unless you do a bit of hacking to the installer files. On such programs, even if you do manage to get them to install they still may not run smoothly, and the audio may sputter, crack, skip and otherwise sound terrible under Rosetta. Most of these troublesome audio programs date pre-2006, but you will still find some of these older (PPC only) version audio programs "bundled" with audio equipment that's still available for sale at some stores or online merchants. In other words, "old stock" is still being sold, which may include some PPC audio software that won't work 100% on an Intel Mac.
Most manufacturers have updated their software since the Intel transition, and many offer updated versions that will work with Intel machines. Check with the software maker for an updated version. Some offer free updates, others charge for it, etc.