One of the big complaints about music synthesizers is that they often sound sterile. "Whenever I listen to electronic music, I feel like something's missing," my shakuhachi teacher once said. It's as if the instrument designer had emulated some aspects of a real-world instrument, but not the more subtle ones that put it in context.
Consider movies, for example. One of the breakthroughs in Star Wars was that the robots looked like they'd lived. They were scraped and dented; black sealant oozed from C3PO's joints. In a horror movie I worked on, I was amused to see the crew smearing dirt around the light switches and doorknobs on the set. But on film, those imperfections made it seem more real.
Back in the world of sound, effects such as reverb go a long way toward making a virtual instrument more lifelike. No one listens to a trumpet with his ear jammed up against the bell. You can also find synthesizers that include performance byproducts such as fret squeaks and breath noise, which add a surprising degree of realism and presence.
But another component of live performance is the audience. Producer Don Was added excitement to the Was (Not Was) track "Just Can't Turn You Loose" by overdubbing cheers from a Tears for Fears concert recording. Listen at the beginning and especially around 1:50:
Reading about an audiophile who compared the crackling of vinyl to the coughing of old men at a concert ("Necessary impurities. Reminders of being in the real world"), I started to imagine a virtual audience plugin. This software would insert random coughs, comments, and ringtones in quiet passages. Or maybe accidental applause between movements in a symphony. Perhaps, like the example above, it could even cheer after each solo.
My TrashTalk plugin would add random comments and audience noises to your audio to make it sound more real. (Apologies to iZotope for skinning its Trash plugin; click to enlarge.)
The next step in virtual instruments: virtual audiences. Imagine how encouraging it would it be to have your own applause-bot! What controls would you add?