The term “saturation” generally refers to a specific type of distortion that emulates the behavior of analog circuits when they’re driven into clipping, which creates harmonic distortion as a result. What most musician’s aren’t aware of is that there are actually 4 types of saturation, as outlined in this excerpt from the latest 6th edition of my Mixing Engineer’s Handbook.
The sound that we consider to be saturated is usually the result of a very slight amount of compression, the addition of even-order harmonics, a gentle roll-off of the high frequencies, and a softening of the transients.
Saturators are used in several mixing scenarios:
- To add extra density to a sound
- To add “glue” to a mix
- To enhance the clarity of a mix element without adding EQ
- To add level without using a compressor
- To give a mix or mix element more excitement, energy, and power
Saturation also introduces soft-knee compression, which means that it gently enters into compression, and the ratio becomes more aggressive as the input increases. For instance, a slight overload of a circuit may apply compression at a ratio of 2:1, but as the input gain is increased, the ratio may also increase to as high as 4:1 or even higher.
There are four types of saturation:
- transformer
- tape
- tube
- transistor
Each type adds a unique flavor and character to your sound, ranging from warm and smooth to gritty and punchy.
Transformer Saturation
A transformer is an electronic component that transfers electrical energy between two or more circuits through electromagnetic induction. It’s primarily used to increase or decrease voltage levels or impedances.
Older analog audio gear used a lot of transformers, which resulted in that smooth “analog” sound that everyone is searching for. Tube (or “valve” if you’re in the UK) gear usually uses more transformers than transistor- (also called “solid state”) based gear.
Just like with other electronic components, it’s possible to overload a transformer by applying a signal that’s hotter than its designed to handle. This is the sound that we’re often looking for when we overdrive the input of an analog preamp like a Neve 1073, but another form of very subtle distortion occurs as well.
Unlike other electronic components used in audio gear, transformer harmonic distortion tends to affect the lower frequencies, which can make the signal sound slightly thicker as a result.
The exact place in the frequency response where this happens is determined by the material that the metal core of the transformer is made of. For instance, steel and nickel cores each affect a different frequency area, but the way a transformer is constructed will also have an effect.
While it’s generally not possible to quickly change transformers in an analog device, it is in digital emulations, and many plugins provide this option.
Kazrog True Iron provides a choice between six popular transformer models, but transformer modes are available in Kush Omega, FabFilter Saturn, and Korneff plugins like the Amplified Instrument Processor, among others.
Tape Saturation
When mixers think of saturation, the first thing that usually pops into their head is the specific instance of tape saturation.
Even though the tape recording may sound really good, it’s inherently a slightly inaccurate reproduction of the original waveform. It’s this inaccuracy that’s partly responsible for what people describe as tape warmth or smoothness, along with transients that have been rolled off so there’s slightly less high frequency content.
At some point, all the particles on the tape become magnetized so there’s none left to align themselves to the incoming waveform. Now even more clipping occurs, and a lot more harmonic distortion is generated.
The sound of analog tape is affected by a number of parameters like tape speed, track width, tape formulation, bias, wow and flutter, and a host of other other adjustments.
That said, you may find some of the parameters available on the tape saturation plugin of your choice. This will end up affecting the frequency response, harmonics, and tape compression, but in most cases the changes will be subtle.
Some popular tape saturation plugins include the Waves J37 and the UAD Studer A800.
Tube Saturation
Tube-based audio gear typically overloads very gently, so it acts like a gentle compressor. The tube saturation results in mostly low-order, even harmonics that provide the “warm” sound that many musicians, engineers, and producers long for.
This type of saturation can give a mix a perceived volume boost without actually increasing the peak volume, as well as a thicker sound with extra “dimension.”
Vocals take especially well to tube saturation, as the low-mids give them an extra warmth that fits nicely in the mix. Adding saturation to a guitar track can make it sound thicker, fuller, and more powerful.
Transistor Saturation
Transistor saturation introduces odd-order harmonics and a form of hard-clipping type of compression. The saturation sounds gritty and aggressive with a good bit of thickness.
Subtle settings provide a smoother saturation, but when driven harder it can add edge and presence to instruments, making them stand out more in a mix. When pushed hard, its impact on transients and higher harmonics can make sounds less punchy and less musical.
Transistor saturation is particularly effective on drums, bass, and electric guitars, producing an emphasis on the midrange frequencies that helps tracks stand out on small speakers.
Transistor saturation emulation plugins include the Soundtoys Decapitator and the FabFilter Saturn.
Go here to find out more about the Mixing Engineer’s Handbook 6th Edition.
