Spectral Processing with the Moog Spectravox: What it is and How to Use it

The Spectravox is an Analog Spectral Processor that is part of the Moog semi-modular family of instruments. In this video, Lachlan goes through how Spectravox works and the different ways you can use it from processing live audio to using it as its own synth voice.

Spectravox as a Filter Bank

At Spectravox’s core is a set of 10 resonant filters that can be used to process and effect external audio or the internal Moog oscillator voice. When using the internal voice, the 10 filters are set at certain bands of frequencies including a low pass on band 1 and a high-pass on band 10. These bands can be shifted up and down the frequency spectrum using the Spectral Shift knob or by modulating it via the in-built LFO and Integrated patch bay. What this means for sound design is that you can sculpt the internal voice and then sweep up or down through the frequency spectrum for interesting and varied tones.

If you are processing external audio, there are a set of 10 analysis filters that analyze the incoming signal and distribute the filters accordingly, allowing you to use Spectravox almost like an EQ by taking out or accentuating certain bands of frequencies. In the video, Lachlan puts a soundscape patch from a Eurorack system through Spectravox and uses the Spectral Shift knob to sweep through the frequencies in the soundscape creating this sparkly and washed sweeping effect. He then automates this by applying the internal LFO to modulate the shift at a certain rate, to take this a step further you could modulate the rate or shape of the LFO by using the patch-bay.

Spectravox as a stand-alone physically modelled voice

As the 10 filters are resonant, we can achieve physical modelling by pinging the filters using external triggers using only certain bands of frequencies. A great way to demonstrate this is the preset Lachlan uses in the video ‘Did I Buy a Marimba?’. In this example Lachlan uses the Moog DFAM’s sequencer to trigger the resonant filters on the Spectravox by using the velocity output of the DFAM. The Spectravox has certain bands of frequencies turned up in order to mimic the harmonic content of a marimba, so the result is a rhythmic marimba like sequence. If we use the Spectral Shift knob we hear that the pitch of the ‘marimba’ changes as we shift up and down the frequency range. So if we take the pitch values out of the DFAM’s sequencer via the patch-bay, we can modulate and sequence where the filters are being shifted in the spectrum thus creating melodies!!

Processing Percussion Through Spectravox while using the Envelope Followers

You’ll notice below band level controls a set of jacks for each band. These are individual envelope followers and CV inputs for the level of the associated filter band. In a nutshell, the envelope follower is a control voltage tracked by the amplitude of that particular band and the CV input jack allows you to modulate that bands level. This allows for a lot of dynamic band frequency modulation when processing external audio or using Spectravox as a Vocoder.

In the video, Lachlan processed a simple kick and snare patch from DFAM through Spectravox. By patching the envelope followers of different frequency bands into the CV input of other bands you can achieve interesting changes to the levels of the filter bands being analysed by Spectravox. This paired with the Spectral Shifter proves to be a deep sound design tool!

Moog Spectravox is available now. Find your nearest dealer HERE