"George Ruch" wrote in message
...

If you let some outside sound through, the system would have to be
designed
to digitally filter the sounds of gun fire. It's possible - I've seen
audio noise reduction systems (dbx, IIRC) that effectively filtered only
the transient noise (clicks, pops, etc.) from vinyl recordings. The
question is would you want to do that if recognizing those sounds and
being
able to place them in your field of hearing could be the difference
between
life and death in a firefight? In that case, simple attenuation may be
the
better solution.

Yes.
You can't just arbitrarily clip the power of a wave form very much
and leave it a recognizable sound. There has to be a proportional
reduction of each part for it to remain the same sound. And if
you want to be able to judge distances by sounds you have to suppress
the not too loud sounds as well.
Simply blanking out moments of excess volume would leave the
troops walking deafly around corners in to firing muzzles.

Perhaps you could substitute a tone that changed in frequency
based on the noise level to let the user know there's loud noises about.