Multi-band saturation is a relatively new form of processing, but an incredibly useful one nonetheless. Essentially, it allows you to saturate individual bands of your frequency response using various forms and amounts of distortion and compression - in turn giving you a lot more control.
Trash 2 by Izotope and Saturn 2 by FabFilter are a couple of examples of processors that offer this type of functionality - but if you know of more, let me know about them in the comments section.
I personally like Saturn 2, and I’ll use gentle saturation on the lows, tube on the low mids, and variations of tape and transformer on the high frequencies.
When you’re saturating your master or full mix-bus, oversampling and linear phase becoming incredibly important - the reason being, affecting your full frequency spectrum can cause aliasing distortion and big phase changes. Oversampling will reduce aliasing distortion and the linear phase will reduce unwanted phase changes.
Saturn 2 offers this functionality, as do some of the Voxengo plugins, but surprisingly a lot do not. However, they’re needed if you want a professional sound.
If you have saturators that you enjoy but they lack this functionality, check out Metaplugin, which lets you increase the sampling rate of the signal prior to it being processed. Also, you can use FIR which isn’t exactly linear phase, but better than using minimum latency filters.
Although other forms of saturation like Tape and Transistor are great at making a master sound full, Tube distortion or saturation has a special formation of harmonics that make it great when mastering. It often introduces a strong second-order harmonic that causes a very full and warm sound.
This may not be the sound you’re going for, so feel free to ignore this or use a different form of saturation, but from personal experience, tube distortion works very well due to this harmonic.
If you’d like to see how your tube distortion or any form of distortion will affect your signal, run a sine wave through it and observe the harmonics that form.
Saturation is really a combination of harmonic distortion and soft-knee compression - this means that you can recreate the effect use a couple of different processors which aren’t directly saturators. Additionally, combining effects to create saturation gives you a lot more control over the timbre of your master or signal.
Let’s combine the Harmonics Processor with the Pro-C 2. We’ll keep the dynamics aspect of the processor off and leave that to the compressor.
I’ll have the compressor first and the harmonics processor second, and use gentle optical compression to achieve a soft-knee setting.
This will be indicative of analog equipment. Then I’ll dial in the distortion.
Automation is a really powerful tool, especially when you use it during a mastering session - automate your saturation to make certain sections of your master stick out. You can simply increase your saturation amount, or change the distortion type resulting in a unique and varied sound.
Personally, this is one of my favorite ways to get a chorus to stick out. I’ll go into the automation settings and increase the level or drive when the chorus hits to make it sound a little more aggressive and to give the master some variance.
For a unique sound, maybe switch between 2 saturator types by bypassing one and switching between the 2 are important points in the track.
You can use multiple saturators during your mastering session to combine unique harmonic formations caused by different saturation and distortion types. For example, combining Tube and Tape saturation is a popular combination that results in a full but clear sound with a complex harmonic makeup.
Tube distortion will introduce low-order harmonics for a full sound, and tape will introduce higher-order ones for a clearer sound. Combined you can balance between the 2 formations and get the right sound.
The BPB saturator is a great free option that you can use for this. It does have an aggressive sound though so be sure to keep the values low and compensate for gain changes.
If you saturate high frequencies, it’s likely that you’ll create harmonics that go above what the processor can handle as set by the sampling rate - in turn creating aliasing distortion. To avoid this, use a higher sampling rate or use a plugin that offers oversampling.
Saturating high frequencies can also sound aggressive in and of itself, even without the effect of aliasing distortion. When you saturate high frequencies, it’s easy to make them too loud and to affect the transients in a way that causes them to sound harsh.
With that said, if you do saturate high frequencies, do so subtly, and use oversampling as a way to reduce aliasing distortion.
