When saturating a signal, it helps to understand that both harmonic distortion and soft-knee compression is occurring. The harmonics and the ratio of compression will depend on the incoming signal, and the component or emulation being used to saturate the signal – like a tube, or transistor.
Fundamentals of Saturation
Saturation occurs when an electrical component, be it a tube, transformer, or magnetic tape can no longer hand the amount of electricity being fed into it. For example, with tape saturation, the magnetic particles in the tape have all been reoriented, but there’s still more signal being input.
This results in both harmonic distortion, and compression which we’ll cover in more detail in subsequent chapters.
Let’s take a quick listen to some saturation so we’re familiar with the effect.
Saturation’s Nonlinear Relationships
Saturation causes a nonlinear relationship being the input and output – in other words, the signal will be compressed, usually gradually or with a soft knee. For example, if an electrical component has been saturated, then it’s likely that for every 3dB of additional input, I’ll get 1dB of output.
In this instance, that ratio would be 3:1, just like with a typical compressor. With saturation, the greater the input after saturation has begun, the higher this ratio.
Let’s listen to how this compression becomes more aggressive, as we push the input’s gain.
Harmonic Formation and Electrical Components
In addition to compression, saturation results in the signal’s distortion, which can be observed as harmonics – or generated frequencies related to the fundamental. Each electrical component will create different harmonic formations, with the most common harmonics being a 2nd and 3rd order, like with Tube and Tape saturation respectively.
Let’s listen to saturation with a 2nd ordered harmonic, then a 3rd, to see if we notice a difference.
Do Even or Odd Harmonics Sound Better?
Both even and odd harmonics can improve the sound of your signal; however, even ordered harmonics have the unique quality of always being in key with the signal. Since a 2nd order is an exact octave, and higher even ordered harmonics are higher octaves, the sound’s harmonious with the fundamental.
With odd-ordered harmonics, they may be in key, but they may also be a note that doesn’t coincide with the notes being played in the song. That isn’t to say they sound bad though, as odd ordered harmonics can add desirable complexity to a signal.
Let’s again take a listen to even and odd harmonics with this information in mind.
Saturation as Upward and Downward Compression
We talked earlier about how saturation causes downward compression due to the nonlinear input to output ratio they create – but they also cause upward compression. The harmonics generated both increase low-level detail and cause a psychoacoustic effect that makes masked signals easier to perceive.
As a result, harmonic lessen the dynamic range, but from the noise-floor up.
Let’s listen to saturation with both downward and upward compression.
The Frequency Response of Saturation
Just like how various electrical components cause different harmonics and different compression ratios, they impart unique changes to the frequency response. This is in part due to the harmonics, since these add signal to various aspects of the frequency range – but it’s also due to the properties of the component.
For example, slower tape will attenuate high frequencies, while amplifying lows. Although this aspect isn’t the direct cause of saturation, it’ll often be directly tied in with saturation, since we’re using these components or emulations of them to saturate the signal.
Let’s listen to tape saturation, with a slower speed and notice the truncated top end and accented lows.
What Makes a Good Analog Emulation?
While we’re on the topic of analog emulation, it may help to know what differentiates a good analog emulated saturator from a not-so-good one. In short, it comes down to how many nuances of the original hardware has been accounted for, and how accurate it’s been emulated.
So a good saturator will account for the nonlinear relationship, as it relates to the incoming frequency, and that frequencies amplitude. It may also account for mild stereo expansion from crosstalk between an incoming stereo signal.
And as we covered, it should account for the unique harmonic formations that occur as they relate to the component, incoming frequency, and amplitude, as well as other factors.
Let’s listen to Satin by U-he, a tape emulation that I think accounts for a lot of the nuances we discussed here.
Saturating with a Regular Compressor
If you have an analog emulation compressor, you can use it for saturation by driving the input while reducing the output. Additionally, you can introduce your compression as you normally would, but set the quickest attack and release times possible to add additional harmonic distortion.
If we think of saturation as a combination of compression and harmonic distortion, then we can use a lot of different plugins to cause saturation.
Frequency Specific Saturation
Frequency-specific saturation has been around since the 1970s when the first exciters added harmonics to the high-frequency range of a signal. Today, we can use a multi-band saturator to affect different ranges – for example, I could add tube distortion to my lows, and tape to the highs.
The tube distortion will cause some lower harmonics, while tape will cause a smooth sound and a 3rd ordered harmonic.
Let’s take a listen to these settings.
Recently, modulated saturation has become an option, in which you can add multiple envelopes and oscillators to affect how the distortion and compression occurs. For example, I could create an ADSR filter and attach it to my drive dial to cause saturation to varying degrees, depending on the incoming signal.
Let’s take a listen to modulated saturation, and notice how it can be used to create unique saturation that isn’t possible with typical saturators.
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