Audified has updated the U73b Compressor, a software model of german U73b Compressor.
U73b is a vintage device and as such it didn't meet present mastering demands: Audified added a bass management button that switches between original sound and desired modern sound (without low frequencies bypass) and they believe that the U73b Compressor now suits better for mastering and processing instruments with fat low end.
Other changes:

• Original device and the first exact software model also shifted phase. In version 1.1 this is now removed.
• Improved VU meter.
• New artist presets by producer Bjorn Thorsrud.
• Level control and many more features.

Price: $149. Download a 30 days unlimited trial version here.

Thanks Larry, have you tried this yet?

I've tried a few mixes with it Since this was modeled from vintage gear & used years ago for mastering vinyl it cuts off a huge amount of the low end,

I used good old Steely Dan for reference while mixing, keeping an instance on the 2 buss for checking. When I mastered I placed it post eq ( along with very light peak /rms reduction using TDR's Kotelnikov pre). It actually enjoyed getting that vintage, un-hyped & overly processed bass that's typical in today's music.
Still punchy with less ear fatigue & better separation.

Works well using HPF too but it was interesting using it as originally designed. Sounds nice on buses, bv's etc.. too.
Still not sure if I'll purchase though.

I tried the demo, and while it sounded nice for some things, I was put off by the low-end rolloff, which for me made it unusable on full mixes or anything with deep bass.  The newest update allows the disabling of the rolloff, which is better.  Still, the very high CPU usage, at least on my system, makes it problematic for mixing.  It's one to keep an eye on, in case they come up with some efficiency improvements.
 
Apparently this is the same outfit behind the Audiffex line of guitar and bass amp sims, including AmpLion and GK Bass.
 
Cheers,
Eddie
 

@Eddie

Are you using it in X3 or the newer SONAR?
I have X3e & with 2 instances it locks up completely. I ran 2 using a different daw & although it still uses more resources I was able to mix no problem, no spiking or dropouts ( along with some new Core6 Acustica plugins to boot)
I wonder if it performs better in new SONAR (Nebula too FTM ) if so I might finally upgrade.
 

carl
Thanks Larry, have you tried this yet?

I've tried a few mixes with it Since this was modeled from vintage gear & used years ago for mastering vinyl it cuts off a huge amount of the low end,

I used good old Steely Dan for reference while mixing, keeping an instance on the 2 buss for checking. When I mastered I placed it post eq ( along with very light peak /rms reduction using TDR's Kotelnikov pre). It actually enjoyed getting that vintage, un-hyped & overly processed bass that's typical in today's music.
Still punchy with less ear fatigue & better separation.

Works well using HPF too but it was interesting using it as originally designed. Sounds nice on buses, bv's etc.. too.
Still not sure if I'll purchase though.

No Carl, haven't tried it...but will download the demo and check it out...Steely Dan rocks!

Carl, I didn't try multiple instances in Sonar before my demo ran out, but I wouldn't be surprised if Sonar didn't play well with this ... Sonar seems to be more finicky than most DAWs when it comes to third-party plugins (e.g. Metric Halo).
 
With other less resource-intensive compressor plugs on hand that sound just as good or better to me than the U73b, I saw no reason to purchase just now. 
 
Cheers,
Eddie
 

Same here. I have another week of the demo left & won't be purchasing.
It does sound nice on buses & certain mixes though, smooth...