Just wondering if there was a way to digitally reduce the background noise like traffic while not changing the actor's dialogue using Sony Vegas 5 or Screenblast Acid 4.0
thanks in advance
City traffic noise is very irregular, so it is difficult to remove (freeway noise is more regular). Even Sony's famous Noise Reduction plug-in has a hard time with that.
Try some EQ to see if you can make the dialogue understandable with just that (the viewer would perhaps expect some traffic noise if you're shooting in the city). Set up a portion to loop and change the EQ settings while listening to the audio. Do NOT use headphones to monitor the audio during editing unless that is your only audience. Any kind of extraneous noise will sound FAR worse in headphones than through speakers.
As a last resort you can use Vegas to go in real close on the audio and remove the noise in the gaps between the actor's lines. Try a small portion first and see if this will work in your situation. Cut on the zero crossings to avoid spikes in the sound.
After removing the noise, you should add some low level background sound for continuity.
For next time, be sure to use headphones to monitor while shooting, anything else is just relying on luck.