Audio Noise Filtering

Procedure: You can get to it through Transform->Noise Reduction or something like that. Here's how to use it:

1. Select a section of the wav file that contains only the noise you want to eliminate.
2. Go to Transform->Noise Reduction.
3. If the option, 'Get Profile From Selection' is greyed out, you have the following options:
   • choose another section of noise that is of longer duration
   • reduce the number of points in the FFT (in NR window)
   • reduce the number of elements in the snapshot (in NR window)
   (Ideally, you want to filter noise with a reasonably large number of FFT points, otherwise the filtering will be incomplete).
4. Click 'Close' (NOT 'Ok').
5. Select only a small portion of the wav--this is just a test to make sure that your noise sample will do the job (this will save you lots of time!)
6. Select the section of the wav that you want to filter the noise from (usually the entire wav).
7. Go to Transform->Noise Reduction, and click 'Ok'.
8. Make sure the desired sound quality was obtained.
9. Edit->Undo what you did.
10. Select the entire wav (or the section that needs to be filtered).
11. Apply the Noise Reduction for real, this time.

If this doesn't clear up the sound well enough, find another section with just the new form of the noise, and try again. Be aware, though, that too much filtering will cause the remaining sample to sound mechanical or tinny. The only way to avoid this problem is not to filter at 100% reduction. (There's a slider on the noise reduction window that can be adjusted to change the level of filtering).

I can't stress enough the advantage to only filtering a small section to test that it reduces the noise effectively. It'll save you lots of time (especially on slower computers)!

It's also to your advantage to save the noise sample FFT spectra--this will simplify your life when you need to filter the hiss caused by a certain microphone from 16 different wav files. (Cool Edit also supports batch processing for this, too!)