Saturation, when talking about audio, is a combination of compression and distortion which is created from overloading the physical components of an electrical system. Distortion, when talking about audio, is the altering of the shape of a waveform which creates a different tonality from that of the original waveform.
It’s pretty common for terms to be used interchangeably in the audio world. Words like saturation, coloration, distortion, harmonic generation, overdrive, crunch, fuzz, etc. are often used in the place of one another.
This happens in any profession or field of study, but the issue with it is that terms begin to lose their meaning.
Saturation can occur with multiple mediums and in many different ways.
Whenever terms are used in an exchange for one another, whether accurately or not, their meanings are conflated - in turn making it more and more difficult for engineers to understand one another when talking audio.
With that said, let’s explore the true meanings of the terms saturation and distortion, where the two overlap, and what makes them different.
We’ll consider terms like harmonics and harmonic generation, which can be used interchangeably with distortion but are a somewhat different concept.
Audio terms get conflated a fair amount, but distortion and saturation are two related, yet different things.
We’ll also take a look at some distortion-based plugins, as well as listen to them to get a better understanding of the sonic differences between distortion and saturation.
Once we’ve defined the differences between distortion, saturation, and some of the nuances like harmonic generation, we’ll look at tube, tape, and transistor based saturation to find out what makes them unique.
Although saturation is thrown around as an audio term today, its origins lie a very real and particular phenomenon in electrical components. When an electrical component can no longer handle the incoming electrical signal, its output becomes non-linear to the input, which results in particular audio effects.
Let’s look into this a bit more to better understand it.
So imagine an incoming electrical signal, being run through an electrical component like a transistor. So long as the incoming electrical signal is within a certain range, it can be output at the same level as the input.
First and foremost, saturation began as an electrical phenomenon.
When the output of a signal is equal to the input, we call that relation linear, due to how it appears on a graph as a linear line.
Saturation is a combination of both compression and distortion.
It looks a lot like a compressor’s graph - in it, we see a linear line that represents an equal input to output ratio. Numerically this is represented as a 1:1 ratio.
When the input and output match, that relationship is called linear due to how it appears on a graph.
This “1:1” ratio should also look familiar, as compressors use the same numerics when displaying the compressor’s ratio. For example, a common compressor ratio is 2:1, meaning that every 2dB of input is output as 1dB.
When the output is no longer linear compression begins.
So what does this have to do with saturation?
In short, saturation is partially compression.
Let’s go back to the electrical component, in which electricity is being run through a transistor. What would happen if the incoming signal became too strong for the physical components of the transistor to handle?
The signal could no longer be output at the same rate it was being inputted, which would lead to a non-linear relationship between the input and output. This is very similar to a compressor’s ratio.
Imagine this graph as it relates to signal that's going in and out of a transistor.
So, if this transistor is being “overloaded” so to speak, then compression will occur. This is the first aspect of saturation - dynamic control and/or compression.
Saturation introduces something called soft-knee compression, which means that the input to output ratio gradually becomes more aggressive. At lower levels of being overloaded, the transistor’s input to output ratio may be 2:1 - but at higher levels, it may be 4:1.
This too can be observed when looking at a compressor, as most have soft-knee settings as an option (the opposite of which is called “hard-knee.”)
A soft-knee compression setting how a lower ratio at quieter levels and a higher ratio at louder levels.
The rate at which a signal is compressed and the curve of this knee depends on the type of electrical component being saturated. A transistor will be saturated differently than a transformer, which will be saturated differently than a tube, and so on.
Considering that these electrical components have different brands, configurations, sizes, and physical makeups, the number of variables is immense - meaning that there are millions of different forms of saturation.
Additionally, the incoming signal, it’s frequency, stereo width, dynamics, and so on will affect this saturation, making this compression via saturation more nuanced and complex than can be comprehended.
Distortion is a big part of saturation.
When a signal becomes saturated enough, through the same process described above, it not only compresses but distorts.
This distortion is an alteration to the shape of the waveform - however, it’s a little more complex than that. When a signal begins to distort, or when the waveform begins to become misshapen, small spikes in amplitude begin to form.
Harmonics show up as spikes in the signal (granted in a much more complex way with more complex waveforms than the one shown above).
These spikes in amplitude are called harmonics. Harmonics are directly tied to the incoming signal in that they are multiples of the original signal - hence the name harmonics as they exist harmoniously with the original signal.
The 200Hz sine wave in this shot is the fundamental frequency.
So let’s say we have a 200Hz sine wave that is being run through a tube at a high enough amplitude to saturate the tube. The saturation causes distortion, which results in the generation of harmonics.
400Hz and 600Hz waves are harmonics generated from saturation.
Let’s say this distortion results in a harmonic at 400Hz and a harmonic at 800Hz. These harmonics are called a 2nd and 3rd order harmonic , with the 1st order being the original 200Hz sine wave.
The fundamental is called the first-order harmonic, the 400Hz wave is the second-order harmonic, and so on.
Harmonic distortion occurs to any signal that saturates an electrical component and varies greatly based on many different variables. These variables include the type of electrical components used, the amount of incoming signal and/or saturation, the frequency and other aspects of the incoming signal, and a lot of other variables.
One example of a random variable that can affect the harmonics would be if the wrong amount of voltage was delivered to the hardware by plugging it in with the wrong power cable. This is just one random variable of many that could potentially affect the type and amplitude of the harmonics created from saturation.
The saturation type depends on many variables.
All this to say that harmonic generation is complex and nuanced, just like the compression caused by saturation.
Now that we understand saturation, as well as what the effect actually is (harmonic distortion and soft-knee compression) let’s look at tube, transistor, and tape saturation.
But first, just in case this distinction was missed, let’s answer “What is Distortion?”
Distortion, as it relates to audio, is the altering of a waveform from its original state and shape. Common forms of distortion include harmonic distortion, noise, intermodulation distortion, phase distortion and cancellation, and bit-depth distortion - all of which can vary greatly depending on multiple variables.
Audio distortion can take many forms, and has a broad definition.
Technically speaking, since distortion is the altering of a waveform from its original state, almost every form of audio processing is a form of distortion.
If you’re equalizing a signal you’re changing the shape of the waveform, if you’re adding reverb you’re changing the shape of the waveform, and so on.
Because audio distortion is defined as change to the shape of a waveform, almost all processing is technically distortion.
But when we think of distortion, we primarily think of harmonic distortion , as its the sound that is most commonly associated with distortion. Keep in mind, however, that distortion is everywhere and in every form of processing - even the cleanest forms of digital processing.
Harmonic distortion is typically what we think of when discussing or imagining distortion.
For example, when a signal is going through A to D conversion, or from an electrical to digital format, small distortions occur.
Because the amplitude of a digital system is dictated by bits, and bits are limited (think of a 16-bit or 24-bit recording) and an electrical signal has theoretically infinite values which it can occupy, a digital recording will have small inaccuracies between the original signal and the digitized signal.
Quantization distortion is the difference between the analog signal and the quantized signal in a digital recording.
The difference between the original signal and the digitized or quantized signal is called quantization distortion and is pretty much noise.
Granted this amount of distortion, especially in 24-bit or 32-bit recordings, is incredibly minuscule ; however, it is still distortion nonetheless.
All this to say that distortion shows up almost anywhere where audio is being processed or reproduced, regardless of whether we can perceive it or not.
There are many more forms of distortion (as listed earlier) but to cover all of them would take some time - so for the time being just know that distortion has a very broad definition and therefore applies to a lot of phenomena in audio processing.
Although different tube types will result in different sounds, tube distortion is often characterized as having a strong second-order harmonic, resulting in an almost doubling effect of the original since. Tube Saturation sounds full when compared to other forms of saturation, as the harmonic generated are lower in pitch.
Tube distortion being emulated by a saturation plugin.
Keep in mind that the harmonics generated, and the amount of compression will depend on a lot of variables , so the description provided above is definitely generalized.
This particular tube emulation presents a strong second-order harmonic, but this truly depends on many variables.
Tube saturation occurs when the diodes in a tube have been electronically saturated or overwhelmed - in other words, no more electrons can travel from the tube’s cathode to the tube’s anode due to a positive charge in the gird between the two components.
A positive charge in a tube inhibits the flow of electrons, in turn compressing its electrical output
Transistor saturation is often characterized by mid to high order harmonic generation, meaning that it causes the signal it distorts to sound brighter and more defined. With that said, Transistor saturation causes the signal it distorts to sound more apparent and cut through busy instrumentation.
A graphic of a transistor.
Again, keep in mind that this description is generalized and will depend on the type of transistor.
Notice that the higher-order harmonics are more prevalent in this particular transistor distortion.
Transistor saturation occurs due to a voltage drop. This voltage drop occurs when the electrical components can no longer sustain the amplitude of the incoming signal.
The electrical layout of a transistor.
Tape saturation is different than other forms of saturation in that it doesn’t include electrical components in the traditional sense but instead has to do with magnetic particles embedded in tape. When a signal is strong enough it re-orients all of the particles available resulting in saturation.
Tape saturation involves the reorientation of magnetic particles embedded in the tape. When the particles can no longer be reoriented, saturation occurs.
Additionally, tape saturation often includes other forms of saturation due to the amplification used to impart the signal onto the tape. These amplifiers often use transistors and tubes, meaning that saturation can occur at multiple points during the signal chain.
For example, a signal can saturate a transistor or tube in the amplifier, and then that saturated signal can saturate the tape if loud enough.
This means that tape saturation has the potential to be the most complex form of saturation.
In short yes, saturation being both harmonic generation and compression can be created digitally via an analog emulation plugin, or by using a distortion and compression plugin. Although digital emulation has become better over the years, analog saturation results in more complex harmonics.
Saturation can be emulated using plugins, but some aspects of it are still missing.
For many, achieving saturation by using analog equipment simply isn’t an option . The reason being, analog equipment is pretty expensive, especially when compared to digital plugins.
In some instances, great-sounding saturation can be achieved with free plugins, giving producers and engineers even more options when they’re on a budget.
Although the availability of saturation is definitely a good thing, it does have to be noted that analog emulation is not the same thing as actual analog processing.
The reason being, countless variables go into analog processing - from the components used, the amount of electricity present, even things like the temperature and humidity of the air and the type of metal used to case the electrical components can have an effect on analog processing.
The many nuanced variables that exist in analog processing, simply don't exist in digital processing.
Yet when it comes to digital processing, these variables simply do not exist. Granted, as digital processing has become more advanced and processing power has increased due to improved computer, more variables can be coded into the software.
However, it will be a long time before this coding can emulate all of or at least most of the variables present in analog and electrical processing.
Again, digital processing is still great, but analog processing is more complex for the time being.
Saturation and distortion are two related, but very different things. As we’ve covered, distortion is a very broad term that refers to the altering of a waveform’s shaping.
One form of distortion that we envision when thinking of distortion is harmonic distortion, which can have a very pleasant or very harsh timbre depending on the amplitude, the type, and the number of harmonics.
Saturation is the combination of harmonic generation and soft-knee compression. Saturation occurs when the electrical components of a piece of hardware are overwhelmed.
When an electrical component is saturated it can no longer output a signal in a linear ratio to the input, resulting in compression and distortion.
Different electrical components like tubes, transistors, and the magnetic particles of tape, each affect a signal different during saturation - resulting in different harmonics, different amounts of distortion, and an overall different timbre.
Although this topic is pretty complex, the most important take away is that the terms distortion and saturation shouldn’t be used interchangeably.
When doing so, the meaning of one term may be conflated or confused with the meaning of the other - in turn making it more difficult for engineers to discuss topics clearly.
That said, it’s best to know these terms and what they mean on a technical level so that they aren’t used incorrectly.