Saturation and Distortion

Saturation and distortion are terms used a lot in audio production and by musicians, but what are they? How do they relate to Overtones and Harmonics as discussed our last article?

Let’s start with distortion. Distortion occurs when an audio signal is too loud for the circuitry it’s running on. This deforms the wave and changes the sound of the audio. The result produced is sometimes pleasing, but often not. It all depends on what we are doing.

Electronics Coach has this great graphic showing what distortion looks like:

Graph showing an distorted audio signal

On the left we see a audio wave form, and on the right we see it distorted. It gets distorted when the wave form goes past the audio threshold (+Vcc & -Vcc). The threshold is how strong of an audio signal the circuit can handle. Anything that goes above it is gets “clipped” off or distorted. This is where the term “clipping” comes from. The more the signal is clipped, the more distorted is sounds.

The earliest distortion was accidental and not desirable. Early audio engineers worked to design circuits that provided maximum clarity. Distortion was viewed as poor use of the hardware, or a failed circuit. Early guitar players experimented with distortion by either ripping their speakers or turning up their tube amp until it distorted naturally. A great example is Howlin’ Wolf’s 1951 recording of “How many more years”.

Another early example of distortion occurred in 1960 on a Marty Robbin’s song “Don’t Worry”. This time, the distortion wasn’t intention but it’s effects would have a major impact.

At the 1 minute 25 second mark in the song the bass player has a solo. His Fender VI bass was unknowingly plugged directly into a mixer channel that was blow. The sound was what is considered the first use of “fuzz” or distortion. The engineer Glenn Snoddy hated it but was convinced to keep the sound. The producer and musicians liked the sound of the fuzz.

When the song was released in 1961 the fuzz sound got a lot of musicians attention. After being asked repeatedly about his secret behind the sound Glenn made the first Fuzz pedal. The first recored use of this was The Ventures song 2,000 Pound Bee, but many other artists used this and a whole industry of effects was launched.

Since then musicians, especially guitarists have used distortion to modify their tone. Without it, popular music music today wouldn’t sound the same. To learn more about the history of distortion Josh Scott with JHS pedals has a great video on it.

Part of the reason distortion is popular isn’t just the “fuzzy” sound it produces. Distortion also amplifies Overtones and Harmonics which we discussed in a previous article. As we turn the volume of an audio source up to distort it, the overtones and harmonics get turned up also making the audio sound more full.

Graph showing the harmonic frequency spectrum
Audio waves clipping

The Image on the left represents a note being played and all the overtones and harmonics that accompany it. Notice that the largest difference between the largest (biggest) wave and the smallest. The note being played rings out clear, while the overtones aren’t audibly noticeable. On the left there are 2 red lines. These represent the loudest the signal can be, or the threshold. Any audio that exceeds this threshold gets clipped or distorted. Notice though that that in the example only the largest wave passes these lines, but the harmonics and overtones don’t. Now the volume difference between the note being distorted and harmonics isn’t as big as it was before. This means the harmonics are louder and more noticeable. To our human ear, we perceive this to sound “fuller”, and in the right application more pleasing.

Distortion isn’t always a good thing though. Some audio sources don’t typically sound good with lots of distortion. For example, vocals for example aren’t typically distorted. We want to hear the singer clearly, unless we want to use distortion as a special effect. This all depends on personal taste.

There is a subtle type of distortion that is musically pleasing, not very noticeable, and gets used quiet often in music production called saturation. Saturation is a combination of both compression and distortion. We won’t get into detail on compression in this article, but a simply explained, compression a tool used to control the of volume of audio, reducing it’s loudest points. So saturation controls the volume and adds a slight amount of distortion. Doing this, it enhances harmonics without adding a lot of deformity to the audio.

Early saturation occurred naturally in many circuits like pre-amps, compressors, equalizers and such. It happened when the circuit or certain components like tubes reacted to the load. In other words, it happened as a limitation of the technology not by design. However, the results were pleasing.

With distortion the harmonics get more noticeable as the signals gets louder and clipped. With saturation those loudest waves get slightly compressed, or turned down, with minimal clipping. The result is a fuller or “warmer” sound without the harsh clipping effect of distortion.

Sage Audio has a great video that goes into detail on saturation:

Today, lots of audio hardware and software is designed to emulate the sound of vintage equipment. This is why vintage audio equipment is so expensive. Just look up the price of a vintage Pultec EQ, or a vintage Neve preamp for example.

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