Technical background:
Simulation of analog sound like saturation from transformers, compressors, tape, EQs,... makes the creation of harmonics necessary.
Hardware:
When analog gear is recorded, it doesn't matter if that gear creates harmonic content exceeding Nyquist frequency, because all A/D-converters use steep lopass filters and get rid of any frequencies above Nyquist frequency (sampling frequency/2) and therefore prevent aliasing artifacts.
48 kHz sampling f = 24 kHz Nyquist = highest detectable frequency
ITB:
If harmonics are created by plugins, frequencies within the plugin are created which easily could exceed the current Nyquist frequency of the project.
For example smashing hihats or cymbals (which have significant amplitudes in the 10 kHz range) with a compressor and/or tape saturation, means - for example - the 3rd harmonics of the 10 kHz already appear @30 kHz.
That means, if the DAW runs @44 kHz (Nyquist = 22 kHz) and the plugin developer does not care abut that problem, that 3rd harmonics created in the plugin will appear below Nyquist in the audible treble range at 14 kHz.
example 4th harmonics of 10 kHz = 40 kHz -> that inaudible 4th harmonics of 10k reappears at 4 kHz in the audible range...
So an aliased 14 kHz / 4 kHz signal is added to the cymbals track (ofcourse not only these two frequencies, because the cymbals are not only @10 kHz, but all harmonic multiples of the frequencies in the original signal above Nyquist are folded down into the audible range).
In contrast any recorded analog gear would be free of these aliasing "signals".
What makes things worse: the aliased, downfolded, unwanted frequencies add unwanted signal energy to the frequency range they appear in. They add "treble" energy by adding garbage. They increase signal energy in the mids, but its garbage.
If a SNR of 65 dB is assumed as technically acceptable minimum between the signal and any unwanted "noise" (aliasing frequencies technically are not noise, but are unwanted garbage just like noise), the anti-alias filtering taking place in the plugin should keep any harmonics below that level.
It should also be kept in mind, that usually lots of additional processing is taking place with the signal after harmonic content has been added by a plugin: once a "analog" plugin has injected audible aliasing garbage into the signal, its not possible to get rid of it ever again.
I used Plugindoctor for testing. The results were surprising to me.
Sometimes especially the big names in the industry seem not to use even the most basic anti-aliasing filters and allow 100% aliasing garbage to be injected into the audio signal.
But on the other hand, I am very pleased to see less widely known names obviously doing lots of good things to prevent the aliasing garbage from becoming audible.
Screenshots showing results to follow...
List of tested plugins:
Analog Obsession STEQ
Testing Aliasing of Plugins (measurements)
Audified RZ062
Testing Aliasing of Plugins (measurements)
BBE Harmonic Maximizer
Testing Aliasing of Plugins (measurements)
BOZ Little Clipper
Testing Aliasing of Plugins (measurements)
Brainworx Analog Design Black Box HG-2
Testing Aliasing of Plugins (measurements)
Brainworx Console SSL 4000 G
Testing Aliasing of Plugins (measurements)
Cytomic The Glue
Testing Aliasing of Plugins (measurements)
Cytomic The Scream
Testing Aliasing of Plugins (measurements)
DDMF Magic Death Eye
Testing Aliasing of Plugins (measurements)
DMG Audio TrackComp 2
Testing Aliasing of Plugins (measurements)
Testing Aliasing of Plugins (measurements)
Empirical Labs Arousor
Testing Aliasing of Plugins (measurements)
Testing Aliasing of Plugins (measurements)
Eventide Omnipressor
Testing Aliasing of Plugins (measurements)
Fabfilter Saturn 2
Testing Aliasing of Plugins (measurements)
Fuse Audio Labs VPRE-562A
Testing Aliasing of Plugins (measurements)
Testing Aliasing of Plugins (measurements)
Fuse Audio Labs VQA-154
Testing Aliasing of Plugins (measurements)
IM Multimedia TRacks5 EQ-73
Testing Aliasing of Plugins (measurements)
Izotope Ozone 9 Exciter
Testing Aliasing of Plugins (measurements)
Kazrog True Iron
Testing Aliasing of Plugins (measurements)
Kush Hammer
Testing Aliasing of Plugins (measurements)
Lindell 80 Channel
Testing Aliasing of Plugins (measurements)
SIR Standard Clip
Testing Aliasing of Plugins (measurements)
Softube Saturation Knob
Testing Aliasing of Plugins (measurements)
Softube Harmonic Analog Saturation Processor
Testing Aliasing of Plugins (measurements)
Softube Summit Audio EQF-100
Testing Aliasing of Plugins (measurements)
TDR Kotelnikov GE
Testing Aliasing of Plugins (measurements)
TDR VOS Slick EQ
Testing Aliasing of Plugins (measurements)
Tone Empire Opto Red
Testing Aliasing of Plugins (measurements)
UHE Satin
Testing Aliasing of Plugins (measurements)
Voxengo OVC-128
Testing Aliasing of Plugins (measurements)
Waves Abbey Road Saturator
Testing Aliasing of Plugins (measurements)
Waves CLA-2A
Testing Aliasing of Plugins (measurements)
Waves Kramer HLS
Testing Aliasing of Plugins (measurements)
Waves L1
Testing Aliasing of Plugins (measurements)
Waves Renaissance Channel
Testing Aliasing of Plugins (measurements)
Waves Renaissance Compressor RComp
Testing Aliasing of Plugins (measurements)
Waves Scheps 73
Testing Aliasing of Plugins (measurements)
Waves Scheps Omni Channel
Testing Aliasing of Plugins (measurements)
Waves SSL G-Channel & G-EQ
Testing Aliasing of Plugins (measurements)
Waves VEQ4
Testing Aliasing of Plugins (measurements)