When it comes to altering the tone of sounds within your mixes, the tool you'll likely reach for is equalization, or EQ. EQ lets you modify a sound's harmonic content by adjusting the volume of individual frequency groups. To make a sound brighter, you can amplify the top-end harmonics.
If you want to reduce the boomy low-end sounds, you can use EQ to lower the level of those frequencies. EQ allows you to make either general broad changes or specific surgical ones, targeting narrow problem areas. But the essential thing about EQ is that it only lets you cut or boost frequencies already present in a sound.
Should you decide to add a five-kilohertz boost to an S Wave baseline, nothing will change, as you're trying to amplify frequencies that don't exist in that core sound. It simply won't work. If you want to increase the number of active frequencies in a sound, enhancing its harmonic footprint, you can use distortion and saturation tools.
Turning the concept of distortion into an image, think of sound with a frequency analyzer on. It allows you to see a picture of the sound's harmonics. If you add a filter or processor to a digital image, its appearance alters with color saturation, inversion, flipping, or other changes. The same can be done to audio with distortion tools, modifying active harmonics, and thus altering the sound.
Distortion comes in various forms, and though digitally available as plugins, it used to exist only in the analog realm. It often conjures images of electric guitarists playing through Marshall amps. While musical uses of distortion go far beyond guitarists, amplifier distortion is a useful starting point to understand its effects. Distortion is a catchall term for the process of changing a sound's sonic image.
Within that term, different treatments exist, all altering sounds in subtle or extreme ways. Overdrive, for example, gets its name from boosting the input level into a vacuum tube, becoming a popular effect with guitar amps. Turning the volume to maximum was the only way to overdrive some early amps, creating problems, especially during live performances.
Now, tube-based amps tend to have two controls for volume: input gain and output volume stage. These control the amount of signal level coming into the amp and the final output level, allowing desired distortion at a comfortable volume. Many distortion plugins copy these amp options.
Other amp types available to guitarists are solid-state models, which use transistors rather than vacuum tubes. These offer a cleaner sound, less favored by guitarists looking for more shredding distortion effects. But stompboxes allow distortion outside of the amp, easing the pressure on the amp itself.
Distortion isn't only for guitarists. A unit like the Thermionic Culture Vulture was built for studios, expanding distortion options to a wider range of audio sources. It offers three different types, adding even harmonics for gentler results or odd-numbered harmonics for wilder, thicker treatments.
If you're familiar with subtractive synthesis, there's a parallel with waveforms and harmonics. Adding a second oscillator with a different waveform enriches the sound, making it more complex. This relationship between wave shapes and harmonic content enriches our understanding of distortion.
The Culture Vulture features valves at both the input and output stages, with bias and drive controls varying the amount of current and levels sent. This explains the diverse flavors of distortion, with even minor adjustments making significant changes.
In pre-digital days, tape recording was favored. Engineers found that tape offered a sweet spot where levels could begin to break up, producing a warm, rich color. Pushing the input level too hard led to distortion. Unlike digital distortion with a clear threshold, tape levels offered a dynamic range where softer clipping and saturation produced pleasing results. This has led to the popularity of tape emulation saturation plugins today.
Even digital recording is subject to distortion, with modern workstations now capable of recording at high sample rates and bit depths. This has removed the issue of distortion due to substandard components. But the early days of sampling and digital recording added their own characterful distortion, inspiring the bit crushers we use today.
It's essential to recognize that adding distortion doesn't mean overwhelming your productions with gritty effects. Subtle additions like tape emulation plugins can smooth out transients, qualifying as distortion but sounding very different from overdrive effects in rock guitar solos.
Distortion effects can vary widely, providing crucial parameters for us to manipulate our mixes in either subtle or dramatic ways.