When first attempting to find a place for guitar in electronic music, I binged on downloading any free plug-ins I could get my hands on. Along the way, I discovered a suite of spectral processing effects from Michael Norris. I had no idea what spectral processing was but, hey, they were free. I soon found out they morphed the sound of my guitar in ways unlike anything I had heard. Certainly, nothing in the pedal world created the same ethereal effects.
So, what does the term spectral mean, in this case? When applied to processing it often means the effect is applied differently to different frequency bands of the audio material. Multiband compression is a type of spectral effect, as the compression is applied only to selected frequency ranges of a signal. For example, you might compress just the low end of a mix while leaving the mids and highs more dynamic.
Spectral processing applies this principle to other effects as well. A spectral delay plug-in, such as Artificial Audio Obelisk, allows you to, say, add a long delay with near infinite repeats to the low strings of a guitar in order to create a bass loop, and then solo over that on the more moderately or unaffected high strings (see Figure 1).
Similarly, spectral distortion applies different amounts and types of grit to different parts of the frequency spectrum. You may want the guitar’s midrange to roar, while the low end mildly crunches to avoid conflict with the bass and kick drum. Using a spectral distortion effect such as Izotope’s Trash plug-in lets me apply three different types and amounts of distortion to three frequency ranges of a guitar signal.
Spectral filtering can divide the guitar signal into dozens of frequency bands; imagine a graphic equalizer with 100 or more sliders. This allows you to modify the tone of the guitar in ways that no equalizer—graphic or parametric, or any of the filter pedals currently available—can emulate. Add random modulation of the bands to the mix, and you have something like Jonas Obermueller’s jo.Spectral Morph, a Max for Live plug-in (see Figure 2). It can create morphing, metallic tones that add a haunting spectral ambience, in the phantom-like meaning of the word.
Broadly speaking, the term spectral can refer to sampling along any spectrum of a signal, using amplitude as well as frequency. A Max for Live plugin such as opticon93 Convolvor performs cross synthesis of the input audio and a second signal from one of three sources: a sample, an FM synthesizer, or a noise source (see Figure 3). It mixes the first signal with the spectral amplitude of the second, or vice versa. Using Convolvor, I was able to modify my guitar tone with everything from an udu drum to a sample of the sound of my nervous system being tested in a doctor’s office.
Circling back to the Michael Norris Soundmagic Spectral suite that started me down this path, its Emergence plug-in is great for automatic swells, and DroneMaker is excellent for lush pads, while the Idee Fixer plug-in provides an interesting twist on looping (see Figure 4). There are many more cool effects included, but I must warn you the suite hasn’t been updated since 2015 and has a tendency to crash Ableton Live. Still, these effects are so amazing that I recommend you open a special session to create sounds that you can then transfer to your main project.
Red Panda and others are bringing the kinds of granular processing previously available only in software to the guitar pedal world, so it seems likely that someone will eventually bring spectral processing to the stomp box. Until then, all of the above plug-ins, except Obelisk, are free, so start spectralizing.