what is "quiet"?

[Tom Nugent Jr]

People talk about relative noise levels when attempting to use voice 
recognition on their computers.  The various microphones list whether 
they're 'active noise cancelling' or if they require a 'moderately 
quiet' environment.

My question for people is: What counts as quiet?  I'd be using a 
microphone in my at-home office, which is away from everything else. 
About the only regular noise in here is from the fan in my G4 and the 
hard disk on my old G3 laptop.  I guess in the summer I'll have an 
air-conditioner running about 5 feet from my head, and if that's not 
on, sometimes I turn on a fan.  But those are all mostly white-noise 
types of sources, and don't compare in volume to, say, my music if I 
turn it up a bit (I wouldn't play music at all when dictating) or 
even just to a couple of people talking (that is, we don't feel 
distracted or drowned out by the noise).  So, should I really worry 
about a noise-cancelling headset?  Does my office sound like it's 
"moderately" quiet??

Thanks!

  -- Tom