I have used the Noise Reduction in CS5.5 with good results in the past. I have upgraded to CS6 and followed the steps in CS6/Audition 5.0 and sampled a section of the background noise which is from aircraft avionics which has a consistent drone.
The process does reduce some of the background noise but the speach becomes significantly alterered. I have tried a number of ways to try and reduce the background noise while maintaining a reasonable quality of the audio that contains speach.
Any suggestions on how to improve the speach after the noise reduction process?
The effects worked very well previously with the same video clips and background noise so I am not sure if it is something I am doing wrong or a change in the effect process.
Just keep experimenting with the settings.
Have you tried just using a simple highpass filter in Premiere? I edited some footage once with air plane noise and using the highpass filter worked like a charm. Although
I do realize not all planes sound the same so it might not work. Anyways though I just used a highpass and set it to like 160 or 170.
If you can isolate a couple of seconds of just noise, then the Adaptive Noise Reduction effect can do a really good job of reducing the noise and not altering the speech beyond acceptable limits.
That said, you may get help that is better targeted if you post your question in the Audition forum.