Platform: PC, Linux
Acustica Nebula VST plug-in holds the honor of offering the best free reverb on the planet. They use a process called Volterra Kernal Modeling, based on their Volterra Kernel Series. It emulates different types of vintage gear: equalizers, filters, microphones, preamps, compressors, reverb and time-variant processors like chorus, flangers, and phasers. I don't pretend to understand how it works, although I've read a bit about it. The closest analogy I can give you is that it is somewhat similar to how convolution reverb works. One way they are similar is that it uses more processing power than a typical plug-in, but the pay-off is dramatic.
At the other end of the spectrum of reverbs are the algorithmic kind, which are mathematically-based attempts to recreate the acoustic environment of any given space. The fact that it is done with algorithms and not an actual recording tends to make the result more artificial. For some applications this comes across as a cheesy, fake effect. But for others, a high-quality algorithmic reverb is like spreading icing all over a cake. Sure, it's not the real cake, but slathering it all over the top makes the end result more desirable.
The Holy Grail of all algorithmic reverbs is indisputably the Lexicon 480L and it's more recent brother, the 960L. These are dedicated hardware boxes that do nothing but crunch the numbers necessary to get that unmistakable high-quality sound that you hear on many big budget records, especially on the vocals. Acustica used their Volterra Kernal technology to emulate them both, and they did a fantastic job. If you have a studio full of freeware and you want to fool the masses by the high quality of your recordings, be sure to add the Acustica Nebula Free to your VST toolkit.
* Be prepared: Nebula is kind of a pain to get and to install, but I promise that you will not regret the initial single investment of time. In fact, once you get it going you'll probably be enamored enough to forgive it all it's download and setup difficulties ;-)
* Dynamic Range: 192.5 dB.
* Harmonic Orders: Program-dependent: 0 to 4.
* Internal Bit Rate:
+ 64 bit floating point for optimizations 1, 3, 4.
+ 80 bit floating point for optimizations 2, 5, 6, 7.
o Control Sources:
+ 64 bit floating point.
* In/Out Bit Rate: 32 bit floating point.
* Incredible range of Frequency Rates from 6Khz to 384Khz with many small intervals.
There are two versions of Nebula available for free; Nebula 2 and Nebula 3, and even a dedicated Hispanic version of v3. Both sound fantastic and have their own individual free libraries available. Might as well get 'em both!
The Lexicon PSP-42 sells for $149
the Lexicon Pantheon Reverb is
only available bundled with hardware.