"Spectral Subtraction Noise Sample" is Grayed-Out, Disabled

[johnywhy]

how to enable?

thx

[johnywhy]

i figured it out. 

1. Select region about 3 seconds or more, which contains absolutely nothing, except perfectly uniform, consistent noise. 
2. Click Effects > Cleanup > Noise Reduction > Grab Noise Sample. 
3. Select new region. 
4. Click Effects > Cleanup > Noise Reduction > Spectral subtraction based on noise sample. 

cheers!