I thought I would share my test results with several plug in compressors for mastering on a blues (Stevie Ray) song I recorded, and a smooth jazz song.
1. Waves V Series: Transparent comp that is able to smooth out the hard dynamics in a gentle way making them more even with the rest of the song. Very nice for mastering. I was able to get good results rather quickly.
I preferred 1.5 ratio with meters going up to -2.0db.
Attack fast with release on auto.
I tried harder threshold of up to -6db; it made the dynamics too soft for my tests.
2. Waves SSL comp: Punchy, clean but controlled. Not as smooth as the V comp. I found the attack on 0.3, and 0.1 the comp was too grabby for my taste on both songs. I preferred the attack at 1 mill. Ratio on 2. I like this comp on the blues number but it did nothing for me on the jazz.
3. Waves API 2500 comp: This sounded in between the SSL and V comp. Not as sharp as the SSL, but not as smooth as the V comp. Good control. The fast attack was not as grabby as the SSL. Ratio was at 2 and release on 5. Sounded great on both songs. On the blues number it controlled the transients without getting in the way. When the attack was on 0.3 it was too faster on the kick. 0.1 was better and 1.0 was even better.
4. UAD Fairchild: It sounded like a heavy handed V Series. A little sticky and smoother. Eh, it was ok. People like mastering engineer Massive Mastering advised it takes too much of the low end out.
5. Waves Ren Comp: This offers Eletro or Opto, and smoother and warm options.Warm adds a slight haz to the signal. I preferred the smooth button active. I also preferred opto for mastering. I really have liked this compressor for guitars, and bass, but for mastering, it did not do anything for me.
6. Samplitude's Ammunition compressor: This controlled the dynamics but still allowed the songs to breath. Clean, but controlled. So much controls like side chain, M/S, compressor mix, HP filters, that you can obtain so many different sounds to your signal. Hands down the more powerful plug in compressor I have ever used.
7. Waves Linear mastering compressor. I used this with the threshold controlling each band the together so it worked more like a stereo compressor. I used the opto mastering setting and slided the threshold until the strong dynamics were controlled. I found it kept the same integrity in the music while controlling the hard kicks are bass guitar parts. This is very clean, not adding artifacts and was a good controlled compressor. This compressor is not talked about much on the forums, but I really like it. Especially for those who cannot afford a GML Dynamic Controller or Cranesong ST-8.
I liked the Samplitude Ammunition compressor the best. I might even use two together with each having a different purpose. I might also want to use it with the V Series. The V could gently add a subtle clean smoothness, while Ammunition and control transients, and with its' other controls, but used like an L2 limiter but this is a cleaner more open sounding limiter. Waves Mastering compressor was good to control transients without affecting the music as much. With this being a linear comp, it is very clean
I liked the API on the blues number, but think it would be better on a drum or 2 bus. SSL was good if you want a song to be punchy and forward.
Though some are very useful, I have not found any to take place of something like a Manley Vari Mu, Pend OCl-2, or GML Dynamic Controller.