You are here

Moog Spectravox

Semi-modular Spectral Processor By Robin Bigwood
Published November 2024

Moog Spectravox

This new addition to the Moog semi‑modular 60HP range is a little hard to pin down, so what exactly is the Spectravox?

Along with the Labyrinth (reviewed in our August 2024 issue), the Spectravox is Moog’s newest semi‑modular standalone and Eurorack‑compatible device, joining the well‑known Mother‑32, DFAM and Subharmonicon, with similar compact form factor, styling, and high‑quality construction.

It would be easy to assume the Spectravox is just an analogue vocoder — not that there are very many of those out there — but in fact it’s a multi‑function unit that should have much wider appeal. Under the hood it has a true analogue vocoder’s requisite pair of filter banks and accompanying facilities, and I note with some kind of miserly delight that it undercuts the currently available, hefty Moog 16‑channel vocoder reissue by about £4500.

However, it’s also possible to use the Spectravox only as a filter bank, routing into it mono audio from elsewhere and enjoying tone‑shaping possibilities that lie somewhere between those of synth filters and EQ. In this role there’s a direct lineage to the Moog 907 Fixed Filter Bank, used in various full‑size modulars. In fact, a Spectravox can do things a 907 can’t. The first is to introduce resonance in each filter band, and the second to move or ‘shift’ the filter frequencies, jointly and relatively, making the Spectravox more of an ‘unfixed’ bank, if you like. Spectral Shift (as it’s called) can be done manually, or an onboard, hardwired LFO can do it for you, with scope for liquid, phaser‑like sweeps or resonant sirens.

Finally, for distinctly good measure, the Spectravox is a simple synth voice as well, which can act as the harmonically rich carrier component for the vocoder, or can be utilised independently. It has a single oscillator with sawtooth and variable‑width pulse waves alongside a white‑noise source. The provided envelope generator is a basic thing, with an instant attack, variable decay, and no sustain phase, but it can help to create percussive sounds. Pulse‑width modulation, vibrato and more can also be achieved using the shift LFO, via the patchbay.

Say ‘Uhh’?

The way these elements interact when you approach a Spectravox for the first time may not be glaringly obvious. The only non‑modular connections (other than for the 12V 2.0A mains adaptor) are a quarter‑inch rear‑panel mono line‑level output that also doubles as a headphone out, and a front‑panel XLR/jack combi ‘Program Input’. In contrast with many digital vocoder alternatives on the market there’s no MIDI, so the onboard synth cannot be played that way. The included quick start guide isn’t a great help either, being extremely light on practical, useful information. The downloadable full PDF manual is much more what we’ve come to expect from Moog, includes some fascinating historical context, and has a vital ‘Exploring Spectravox’ section with some setup walkthroughs. A clutch of patch overlay cards are useful too, but you’ll still get the most out of those after you’ve read the PDF. In the end, and after some experimentation, it all makes sense, and there’s a lot to enjoy.

Like the other models in the range, the Spectravox’s front panel is 60HP wide and can be removed from the case and fitted into a Eurorack system.Like the other models in the range, the Spectravox’s front panel is 60HP wide and can be removed from the case and fitted into a Eurorack system.

Filter Fabric

Much as I’d love to (yet again) pull on my full flower‑power get‑up and dive into the Spectravox in its role as a vocoder, it makes more sense to consider it as a filter bank first. So the lab coat it is...

Getting into this mode, and others, is a matter of appropriately juggling the three switches at the lower right. Then, with no external patching, you’ll hear the internal oscillator routed through the filters. External signals go into the 3.5mm Carrier patch point on the front panel and break the internal synth connection. Actually, you can also use the XLR/quarter‑inch combi socket: on its own it won’t get routed to the right place, but patching Program output to Carrier input solves that. The mic input does not supply phantom power, incidentally, but its gain knob was able to tease out healthy signals from various dynamic mics I tested it with. An accompanying LED indicates signal level with varying brightness, but is a blunt tool as meters go.

In no time it emerges that the Spectravox’s filter bank — the one used to sculpt and shape external signals — is flexible, can pull off some interesting and remarkable tone transformations, and has plenty of character. It’s distinctly unlike the vast majority of single‑band synth filters we’re all used to and is full of practical and creative potential.

At the same time, it is not a Moog 907 emulation. Where the rare handmade module has filters tuned to two harmonically‑related stacks (250, 500, 1000, 2000 Hz, alongside 350, 700, 1400 and 2800 Hz, plus low‑ and high‑pass filters), the Spectravox offers the funkily inharmonic line‑up of 230, 320, 560, 830, 1200, 1700, 2300, 3200, 4500 and 5400 Hz when the Shift knob is at its default central position. You can then swing frequency centres sufficiently that the lowest band will go almost subsonic at one extreme, and the highest band ultrasonic at the other. A 907 can only dream of that.

Where they are similar though is in the way that the pots provided for each band are all attenuators. You can only cut the level for a band, never boost it, but attenuation can be complete in that if you turn down all bands at once you’ll get silence. On the Spectravox attenuator pots are of the skinny love‑’em‑or‑hate‑’em kind, but I understand an official knurled pot kit is available to purchase to help those of the latter persuasion.

Because of the inherent coloration associated with the Carrier filter bank, a huge timbral range can be teased out of a simple single oscillator. To illustrate the point, the three waveforms here are all Spectravox pulse waves. The first is sourced direct from the VCO output, and is the raw, ‘accurate’ pulse straight from the oscillator. The second is from the main output with Shift in its central position. The third — basically a triangle wave — has Shift turned 90 degrees left. The crucial thing here is that all filter bands were wide open at all times: a further range of wave shapes emerge when you start to use them.Because of the inherent coloration associated with the Carrier filter bank, a huge timbral range can be teased out of a simple single oscillator. To illustrate the point, the three waveforms here are all Spectravox pulse waves. The first is sourced direct from the VCO output, and is the raw, ‘accurate’ pulse straight from the oscillator. The second is from the main output with Shift in its central position. The third — basically a triangle wave — has Shift turned 90 degrees left. The crucial thing here is that all filter bands were wide open at all times: a further range of wave shapes emerge when you start to use them.Moog SpectravoxMoog SpectravoxFilters 2‑9 are band‑pass types, with overlapping 6dB/octave slopes (as far as I can make out, squinting at my spectrum analyser). The slope flattens and broadens a touch in the upper 30 degrees or so of pot travel. Moog call filter 1 a low‑pass, and 10 a high‑pass, and on the control panel that’s reinforced by little response curve graphics. In practice they behave much like additional band‑passes in their relative positions, albeit with filter 1 exhibiting more of a shelf‑type response over low‑end frequency content. You could even argue that they’re named the wrong way round, according to the way they often behave. Certainly filter 10 removes high frequencies, pure and simple, which is not most...

You are reading one of the locked Subscribers-only articles from our latest 5 issues.

You've read 30% of this article for free, so to continue reading...

  • ✅ Log in - if you have a Subscription you bought from SOS.
  • Buy & Download this Single Article in PDF format £1.00 GBP$1.49 USD
    For less than the price of a coffee, buy now and immediately download to your computer or smartphone.
     
  • Buy & Download the FULL ISSUE PDF
    Our 'full SOS magazine' for smartphone/tablet/computer. More info...
     
  • Buy a DIGITAL subscription (or Print + Digital)
    Instantly unlock ALL premium web articles! Visit our ShopStore.

RECORDING TECHNOLOGY: Basics & Beyond
Claim your FREE 170-page digital publication
from the makers of Sound On SoundCLICK HERE