scook
ReaFIR is part of the ReaPlugs package

This is what I use for a free solution.  
 
Results vary based on multiple factors, but it certainly create a profile and then you can adjust the floor of where it starts cutting that out.  

https://youtu.be/sctKIMAunhk
 
I made this video to show some things I did to remove noise from some cassette tape recordings over the weekend.

A lite version of Sony's Sound Forge came with a Sony USB turntable I bought. I had helped a friend set his up and I was impressed at the ease of use factor for ripping old records. So I bought one for myself.  I didn't expect free software that comes with a $120  turntable to be that good. But it totally removed the normal pops and crackles standard fare for vinyl. They got that one dialled in. 
Haven't tried it on recording noise yet because I haven't had a noisy project handed to me for a long time. Used to do a lot of that work but now I hide from those people.... 
 
I think I'll add it to my tools menu and give it a try.. Mostly I use Wave lab, but my version, Elements, does not include anything like that.  
And thank's for posting the link to your handy tool again Steve,, It's hard to find... 

Sorry for the daisy chain of posts, but here is a link to a post with the same question. That post has the link buried in it for Adobe Creative Suite 2.0 (c. 2006, IIRC). For some reason, finding that initial post is a PITA.
 
Also, adding Audition to the Utilities menu makes noise reduction quick. I posted a video on that a while back and put the registry edit in the comments (sorry for more links), but scook has a utility he made to make this less painful.
 
I should pull all of this information into a consolidated post at some point but seem to run out of time when it comes to mind.
 
 

I would LOVE to see someone make a plugin of the old Symetrix 511A downward expander - one of THE best noisegates I ever used in hardware form. It was basically a Hi Frequency EQ with intelligent variable gain that would ride on top of the hiss... hard to describe but genius to use.

I use a stand alone product called Diamond Cut.  It is mainly for Audio restoration of records and tapes to digital audio, but it does have the type of filter you talk about.
 
http://www.diamondcut.com/store/index.php?main_page=product_info&cPath=1&products_id=31http://www.diamondcut.com/store/index.php?main_page=product_info&cPath=1&products_id=31
 
The version I have is much older, but still works.  One note is that it does not work on MP3 files, WAV only.

LJB
I would LOVE to see someone make a plugin of the old Symetrix 511A downward expander - one of THE best noisegates I ever used in hardware form. It was basically a Hi Frequency EQ with intelligent variable gain that would ride on top of the hiss... hard to describe but genius to use.

I'm pretty sure most multiband compressors/expanders can do this (e.g. Pro-MB by FabFilter) or a dynamic EQ like Melda's MDynamicEQ.

Sanderxpander

LJB
I would LOVE to see someone make a plugin of the old Symetrix 511A downward expander - one of THE best noisegates I ever used in hardware form. It was basically a Hi Frequency EQ with intelligent variable gain that would ride on top of the hiss... hard to describe but genius to use.

I'm pretty sure most multiband compressors/expanders can do this (e.g. Pro-MB by FabFilter) or a dynamic EQ like Melda's MDynamicEQ.

Can the same be said about Sonitus EQ/Multiband OR the LP/LP-64 EQ/MB ?
If not, why not and why & how are the others different ?
And if they can do the same, why aren't we talking enough about them ? It would be nice to get things done with what's available within Sonar, wouldn't it ?
 

Mainly because I'm not sure if they can. Feel free to check.

You need an expander. Compressors are the opposite. You want to reduce volume when the sound level is soft.. not loud. Preferably, within narrow ranges on the spectrum. Zero attack... fast. Quick release.

This is why the Melda tool I demo in the video works well for this job.

I'm pretty sure cakewalk does come with an expander. I just can't remember. Sonitus? Craig, help me out here?